text: Fix incomplete invalidation

When a style change affects the text, we need to
clear the cached content, in order to pick up the
new text style.

.gitlab-ci.yml

@@ -1,7 +1,7 @@
 stages:
   - build
   - flatpak
-  - deploy
+#  - deploy
 
 .cache-paths: &cache-paths
   paths:
@@ -101,20 +101,19 @@ flatpak-master:icon-browser:
     APPID: org.gtk.IconBrowser4
   <<: *flatpak-master
 
-pages:
-  image: registry.gitlab.gnome.org/gnome/gtk/master:v6
-  stage: deploy 
-  script:
-    - meson -Ddocumentation=true _build .
-    - ninja -C _build
-    - ninja -C _build gdk4-doc gsk4-doc gtk4-doc
-
-    - mkdir -p public/
-    - mv _build/docs/reference/gtk/html/ public/gtk/
-    - mv _build/docs/reference/gdk/html/ public/gdk/
-    - mv _build/docs/reference/gsk/html/ public/gsk/
-  artifacts:
-    paths:
-      - public
-  only:
-    - master
+#pages:
+#  image: registry.gitlab.gnome.org/gnome/gtk/master:v6
+#  stage: deploy 
+#  script:
+#    - meson -Dgtk_doc=true _build .
+#    - ninja -C _build
+#    - ninja -C _build gdk4-doc gsk4-doc gtk4-doc
+#    - mkdir -p public/
+#    - mv _build/docs/reference/gtk/html/ public/gtk/
+#    - mv _build/docs/reference/gdk/html/ public/gdk/
+#    - mv _build/docs/reference/gsk/html/ public/gsk/
+#  artifacts:
+#    paths:
+#      - public
+#  only:
+#    - master

config.h.meson

@@ -56,12 +56,6 @@
 /* Define if GStreamer support is available */
 #mesondefine HAVE_GSTREAMER
 
-/* Define to 1 if you have the `httpGetAuthString' function. */
-#mesondefine HAVE_HTTPGETAUTHSTRING
-
-/* Define if cups http_t authstring field is accessible */
-#mesondefine HAVE_HTTP_AUTHSTRING
-
 /* Define to 1 if you have the <inttypes.h> header file. */
 #mesondefine HAVE_INTTYPES_H
 

demos/constraint-editor/constraint-editor-application.c

@@ -0,0 +1,115 @@
+/*
+ * Copyright © 2019 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Authors: Matthias Clasen
+ */
+
+#include "config.h"
+
+#include "constraint-editor-application.h"
+#include "constraint-editor-window.h"
+
+struct _ConstraintEditorApplication
+{
+  GtkApplication parent_instance;
+};
+
+G_DEFINE_TYPE(ConstraintEditorApplication, constraint_editor_application, GTK_TYPE_APPLICATION);
+
+static void
+constraint_editor_application_init (ConstraintEditorApplication *app)
+{
+}
+
+static void
+quit_activated (GSimpleAction *action,
+                GVariant      *parameter,
+                gpointer       data)
+{
+  g_application_quit (G_APPLICATION (data));
+}
+
+static GActionEntry app_entries[] =
+{
+  { "quit", quit_activated, NULL, NULL, NULL }
+};
+
+static void
+constraint_editor_application_startup (GApplication *app)
+{
+  const char *quit_accels[2] = { "<Ctrl>Q", NULL };
+  const char *open_accels[2] = { "<Ctrl>O", NULL };
+  GtkCssProvider *provider;
+
+  G_APPLICATION_CLASS (constraint_editor_application_parent_class)->startup (app);
+
+  g_action_map_add_action_entries (G_ACTION_MAP (app),
+                                   app_entries, G_N_ELEMENTS (app_entries),
+                                   app);
+  gtk_application_set_accels_for_action (GTK_APPLICATION (app), "app.quit", quit_accels);
+  gtk_application_set_accels_for_action (GTK_APPLICATION (app), "win.open", open_accels);
+
+  provider = gtk_css_provider_new ();
+  gtk_css_provider_load_from_resource (provider, "/org/gtk/gtk4/constraint-editor/constraint-editor.css");
+  gtk_style_context_add_provider_for_display (gdk_display_get_default (),
+                                              GTK_STYLE_PROVIDER (provider),
+                                              GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);
+}
+
+static void
+constraint_editor_application_activate (GApplication *app)
+{
+  ConstraintEditorWindow *win;
+
+  win = constraint_editor_window_new (CONSTRAINT_EDITOR_APPLICATION (app));
+  gtk_window_present (GTK_WINDOW (win));
+}
+
+static void
+constraint_editor_application_open (GApplication  *app,
+                                    GFile        **files,
+                                    gint           n_files,
+                                    const gchar   *hint)
+{
+  ConstraintEditorWindow *win;
+  gint i;
+
+  for (i = 0; i < n_files; i++)
+    {
+      win = constraint_editor_window_new (CONSTRAINT_EDITOR_APPLICATION (app));
+      constraint_editor_window_load (win, files[i]);
+      gtk_window_present (GTK_WINDOW (win));
+    }
+}
+
+static void
+constraint_editor_application_class_init (ConstraintEditorApplicationClass *class)
+{
+  GApplicationClass *application_class = G_APPLICATION_CLASS (class);
+
+  application_class->startup = constraint_editor_application_startup;
+  application_class->activate = constraint_editor_application_activate;
+  application_class->open = constraint_editor_application_open;
+}
+
+ConstraintEditorApplication *
+constraint_editor_application_new (void)
+{
+  return g_object_new (CONSTRAINT_EDITOR_APPLICATION_TYPE,
+                       "application-id", "org.gtk.gtk4.ConstraintEditor",
+                       "flags", G_APPLICATION_HANDLES_OPEN,
+                       NULL);
+}

demos/constraint-editor/constraint-editor-application.h

@@ -0,0 +1,28 @@
+/*
+ * Copyright © 2019 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Authors: Matthias Clasen
+ */
+
+#pragma once
+
+#include <gtk/gtk.h>
+
+#define CONSTRAINT_EDITOR_APPLICATION_TYPE (constraint_editor_application_get_type ())
+
+G_DECLARE_FINAL_TYPE (ConstraintEditorApplication, constraint_editor_application, CONSTRAINT, EDITOR_APPLICATION, GtkApplication)
+
+ConstraintEditorApplication *constraint_editor_application_new (void);

demos/constraint-editor/constraint-editor-window.c

@@ -0,0 +1,639 @@
+/*
+ * Copyright © 2019 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Authors: Matthias Clasen
+ */
+
+#include "config.h"
+
+#include "constraint-editor-window.h"
+#include "constraint-view.h"
+#include "constraint-editor.h"
+#include "guide-editor.h"
+
+struct _ConstraintEditorWindow
+{
+  GtkApplicationWindow parent_instance;
+
+  GtkWidget *paned;
+  GtkWidget *view;
+  GtkWidget *list;
+};
+
+G_DEFINE_TYPE(ConstraintEditorWindow, constraint_editor_window, GTK_TYPE_APPLICATION_WINDOW);
+
+static GtkConstraintTarget *
+find_target (GListModel *model,
+             GtkConstraintTarget *orig)
+{
+  const char *name;
+  const char *model_name;
+  gpointer item;
+  int i;
+
+  if (orig == NULL)
+    return NULL;
+
+  if (GTK_IS_LABEL (orig))
+    name = gtk_label_get_label (GTK_LABEL (orig));
+  else if (GTK_IS_CONSTRAINT_GUIDE (orig))
+    name = gtk_constraint_guide_get_name (GTK_CONSTRAINT_GUIDE (orig));
+  else
+    {
+      g_warning ("Don't know how to handle %s targets", G_OBJECT_TYPE_NAME (orig));
+      return NULL;
+    }
+  for (i = 0; i < g_list_model_get_n_items (model); i++)
+    {
+      item = g_list_model_get_item (model, i);
+      g_object_unref (item);
+      if (GTK_IS_WIDGET (item))
+        model_name = gtk_widget_get_name (GTK_WIDGET (item));
+      else
+        model_name = gtk_constraint_guide_get_name (GTK_CONSTRAINT_GUIDE (item));
+
+      if (strcmp (name, model_name) == 0)
+        return GTK_CONSTRAINT_TARGET (item);
+    }
+  g_warning ("Failed to find target '%s'", name);
+
+  return NULL;
+}
+
+gboolean
+constraint_editor_window_load (ConstraintEditorWindow *self,
+                               GFile            *file)
+{
+  char *path;
+  GtkBuilder *builder;
+  GError *error = NULL;
+  GtkWidget *view;
+  GtkLayoutManager *layout;
+  GtkWidget *child;
+  const char *name;
+  gpointer item;
+  int i;
+  GListModel *list;
+
+  path = g_file_get_path (file);
+
+  builder = gtk_builder_new ();
+  if (!gtk_builder_add_from_file (builder, path, &error))
+    {
+      g_print ("Could not load %s: %s", path, error->message);
+      g_error_free (error);
+      g_free (path);
+      g_object_unref (builder);
+      return FALSE;
+    }
+
+  view = GTK_WIDGET (gtk_builder_get_object (builder, "view"));
+  if (!GTK_IS_BOX (view))
+    {
+      g_print ("Could not load %s: No GtkBox named 'view'", path);
+      g_free (path);
+      g_object_unref (builder);
+      return FALSE;
+    }
+  layout = gtk_widget_get_layout_manager (view);
+  if (!GTK_IS_CONSTRAINT_LAYOUT (layout))
+    {
+      g_print ("Could not load %s: Widget 'view' does not use GtkConstraintLayout", path);
+      g_free (path);
+      g_object_unref (builder);
+      return FALSE;
+    }
+
+  for (child = gtk_widget_get_first_child (view);
+       child;
+       child = gtk_widget_get_next_sibling (child))
+    {
+      if (!GTK_IS_LABEL (child))
+        {
+          g_print ("Skipping non-GtkLabel child\n");
+          continue;
+        }
+
+      name = gtk_label_get_label (GTK_LABEL (child));
+      constraint_view_add_child (CONSTRAINT_VIEW (self->view), name);
+    }
+
+  list = gtk_constraint_layout_observe_guides (GTK_CONSTRAINT_LAYOUT (layout));
+  for (i = 0; i < g_list_model_get_n_items (list); i++)
+    {
+      GtkConstraintGuide *guide, *clone;
+      int w, h;
+
+      item = g_list_model_get_item (list, i);
+      guide = GTK_CONSTRAINT_GUIDE (item);
+
+      /* need to clone here, to attach to the right targets */
+      clone = gtk_constraint_guide_new ();
+      gtk_constraint_guide_set_name (clone, gtk_constraint_guide_get_name (guide));
+      gtk_constraint_guide_set_strength (clone, gtk_constraint_guide_get_strength (guide));
+      gtk_constraint_guide_get_min_size (guide, &w, &h);
+      gtk_constraint_guide_set_min_size (clone, w, h);
+      gtk_constraint_guide_get_nat_size (guide, &w, &h);
+      gtk_constraint_guide_set_nat_size (clone, w, h);
+      gtk_constraint_guide_get_max_size (guide, &w, &h);
+      gtk_constraint_guide_set_max_size (clone, w, h);
+      constraint_view_add_guide (CONSTRAINT_VIEW (self->view), clone);
+      g_object_unref (guide);
+      g_object_unref (clone);
+    }
+  g_object_unref (list);
+
+  list = gtk_constraint_layout_observe_constraints (GTK_CONSTRAINT_LAYOUT (layout));
+  for (i = 0; i < g_list_model_get_n_items (list); i++)
+    {
+      GtkConstraint *constraint;
+      GtkConstraint *clone;
+      GtkConstraintTarget *target;
+      GtkConstraintTarget *source;
+
+      item = g_list_model_get_item (list, i);
+      constraint = GTK_CONSTRAINT (item);
+
+      target = gtk_constraint_get_target (constraint);
+      source = gtk_constraint_get_source (constraint);
+      clone = gtk_constraint_new (find_target (constraint_view_get_model (CONSTRAINT_VIEW (self->view)), target),
+                                  gtk_constraint_get_target_attribute (constraint),
+                                  gtk_constraint_get_relation (constraint),
+                                  find_target (constraint_view_get_model (CONSTRAINT_VIEW (self->view)), source),
+                                  gtk_constraint_get_target_attribute (constraint),
+                                  gtk_constraint_get_multiplier (constraint),
+                                  gtk_constraint_get_constant (constraint),
+                                  gtk_constraint_get_strength (constraint));
+
+      constraint_view_add_constraint (CONSTRAINT_VIEW (self->view), clone);
+
+      g_object_unref (constraint);
+      g_object_unref (clone);
+    }
+  g_object_unref (list);
+
+  g_free (path);
+  g_object_unref (builder);
+
+  return TRUE;
+}
+
+static void
+open_response_cb (GtkNativeDialog        *dialog,
+                  gint                    response,
+                  ConstraintEditorWindow *self)
+{
+  gtk_native_dialog_hide (dialog);
+
+  if (response == GTK_RESPONSE_ACCEPT)
+    {
+      GFile *file;
+
+      file = gtk_file_chooser_get_file (GTK_FILE_CHOOSER (dialog));
+      constraint_editor_window_load (self, file);
+      g_object_unref (file);
+    }
+
+  gtk_native_dialog_destroy (dialog);
+}
+
+static void
+open_cb (GtkWidget              *button,
+         ConstraintEditorWindow *self)
+{
+  GtkFileChooserNative *dialog;
+
+  dialog = gtk_file_chooser_native_new ("Open file",
+                                        GTK_WINDOW (self),
+                                        GTK_FILE_CHOOSER_ACTION_OPEN,
+                                        "_Load",
+                                        "_Cancel");
+
+  gtk_native_dialog_set_modal (GTK_NATIVE_DIALOG (dialog), TRUE);
+  gtk_file_chooser_set_current_folder (GTK_FILE_CHOOSER (dialog), ".");
+  g_signal_connect (dialog, "response", G_CALLBACK (open_response_cb), self);
+  gtk_native_dialog_show (GTK_NATIVE_DIALOG (dialog));
+}
+
+static void
+serialize_child (GString   *str,
+                 int        indent,
+                 GtkWidget *child)
+{
+  const char *name;
+
+  name = gtk_widget_get_name (child);
+  g_string_append_printf (str, "%*s<child>\n", indent, "");
+  g_string_append_printf (str, "%*s  <object class=\"GtkLabel\" id=\"%s\">\n", indent, "", name);
+  g_string_append_printf (str, "%*s    <property name=\"label\">%s</property>\n", indent, "", name);
+  g_string_append_printf (str, "%*s  </object>\n", indent, "");
+  g_string_append_printf (str, "%*s</child>\n", indent, "");
+}
+
+static char *
+serialize_model (GListModel *list)
+{
+  GString *str = g_string_new ("");
+  int i;
+
+  g_string_append (str, "<interface>\n");
+  g_string_append (str, "  <object class=\"GtkBox\" id=\"view\">\n");
+  g_string_append (str, "    <property name=\"layout-manager\">\n");
+  g_string_append (str, "      <object class=\"GtkConstraintLayout\">\n");
+  g_string_append (str, "        <constraints>\n");
+  for (i = 0; i < g_list_model_get_n_items (list); i++)
+    {
+      gpointer item = g_list_model_get_item (list, i);
+      g_object_unref (item);
+      if (GTK_IS_CONSTRAINT (item))
+        constraint_editor_serialize_constraint (str, 10, GTK_CONSTRAINT (item));
+      else if (GTK_IS_CONSTRAINT_GUIDE (item))
+        guide_editor_serialize_guide (str, 10, GTK_CONSTRAINT_GUIDE (item));
+    }
+  g_string_append (str, "        </constraints>\n");
+  g_string_append (str, "      </object>\n");
+  g_string_append (str, "    </property>\n");
+  for (i = 0; i < g_list_model_get_n_items (list); i++)
+    {
+      gpointer item = g_list_model_get_item (list, i);
+      g_object_unref (item);
+      if (GTK_IS_WIDGET (item))
+        serialize_child (str, 4, GTK_WIDGET (item));
+    }
+  g_string_append (str, "  </object>\n");
+  g_string_append (str, "</interface>\n");
+
+  return g_string_free (str, FALSE);
+}
+
+
+static void
+save_response_cb (GtkNativeDialog        *dialog,
+                  gint                    response,
+                  ConstraintEditorWindow *self)
+{
+  gtk_native_dialog_hide (dialog);
+
+  if (response == GTK_RESPONSE_ACCEPT)
+    {
+      GListModel *model;
+      char *text, *filename;
+      GError *error = NULL;
+
+      model = constraint_view_get_model (CONSTRAINT_VIEW (self->view));
+      text = serialize_model (model);
+
+      filename = gtk_file_chooser_get_filename (GTK_FILE_CHOOSER (dialog));
+      if (!g_file_set_contents (filename, text, -1, &error))
+        {
+          GtkWidget *dialog;
+
+          dialog = gtk_message_dialog_new (GTK_WINDOW (gtk_widget_get_root (GTK_WIDGET (self))),
+                                           GTK_DIALOG_MODAL|GTK_DIALOG_DESTROY_WITH_PARENT,
+                                           GTK_MESSAGE_INFO,
+                                           GTK_BUTTONS_OK,
+                                           "Saving failed");
+          gtk_message_dialog_format_secondary_text (GTK_MESSAGE_DIALOG (dialog),
+                                                    "%s", error->message);
+          g_signal_connect (dialog, "response", G_CALLBACK (gtk_widget_destroy), NULL);
+          gtk_widget_show (dialog);
+          g_error_free (error);
+        }
+      g_free (filename);
+    }
+
+  gtk_native_dialog_destroy (dialog);
+}
+
+static void
+save_cb (GtkWidget              *button,
+         ConstraintEditorWindow *self)
+{
+  GtkFileChooserNative *dialog;
+
+  dialog = gtk_file_chooser_native_new ("Save constraints",
+                                        GTK_WINDOW (gtk_widget_get_root (GTK_WIDGET (button))),
+                                        GTK_FILE_CHOOSER_ACTION_SAVE,
+                                        "_Save",
+                                        "_Cancel");
+
+  gtk_native_dialog_set_modal (GTK_NATIVE_DIALOG (dialog), TRUE);
+  gtk_file_chooser_set_current_folder (GTK_FILE_CHOOSER (dialog), ".");
+  g_signal_connect (dialog, "response", G_CALLBACK (save_response_cb), self);
+  gtk_native_dialog_show (GTK_NATIVE_DIALOG (dialog));
+}
+
+static void
+constraint_editor_window_finalize (GObject *object)
+{
+  //ConstraintEditorWindow *self = (ConstraintEditorWindow *)object;
+
+  G_OBJECT_CLASS (constraint_editor_window_parent_class)->finalize (object);
+}
+
+static int child_counter;
+static int guide_counter;
+
+static void
+add_child (ConstraintEditorWindow *win)
+{
+  char *name;
+
+  child_counter++;
+  name = g_strdup_printf ("Child %d", child_counter);
+  constraint_view_add_child (CONSTRAINT_VIEW (win->view), name);
+  g_free (name);
+}
+
+static void
+add_guide (ConstraintEditorWindow *win)
+{
+  char *name;
+  GtkConstraintGuide *guide;
+
+  guide_counter++;
+  name = g_strdup_printf ("Guide %d", guide_counter);
+  guide = gtk_constraint_guide_new ();
+  gtk_constraint_guide_set_name (guide, name);
+  g_free (name);
+
+  constraint_view_add_guide (CONSTRAINT_VIEW (win->view), guide);
+}
+
+static void
+constraint_editor_done (ConstraintEditor *editor,
+                        GtkConstraint    *constraint,
+                        ConstraintEditorWindow *win)
+{
+  GtkConstraint *old_constraint;
+
+  g_object_get (editor, "constraint", &old_constraint, NULL);
+
+  if (old_constraint)
+    constraint_view_remove_constraint (CONSTRAINT_VIEW (win->view), old_constraint);
+
+  constraint_view_add_constraint (CONSTRAINT_VIEW (win->view), constraint);
+
+  g_clear_object (&old_constraint);
+
+  gtk_widget_destroy (gtk_widget_get_ancestor (GTK_WIDGET (editor), GTK_TYPE_WINDOW));
+}
+
+static void
+edit_constraint (ConstraintEditorWindow *win,
+                 GtkConstraint          *constraint)
+{
+  GtkWidget *window;
+  ConstraintEditor *editor;
+  GListModel *model;
+
+  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
+  gtk_window_set_transient_for (GTK_WINDOW (window), GTK_WINDOW (win));
+  gtk_window_set_resizable (GTK_WINDOW (window), FALSE);
+  if (constraint)
+    gtk_window_set_title (GTK_WINDOW (window), "Edit Constraint");
+  else
+    gtk_window_set_title (GTK_WINDOW (window), "Create Constraint");
+
+  model = constraint_view_get_model (CONSTRAINT_VIEW (win->view));
+
+  editor = constraint_editor_new (model, constraint);
+
+  gtk_container_add (GTK_CONTAINER (window), GTK_WIDGET (editor));
+
+  g_signal_connect (editor, "done", G_CALLBACK (constraint_editor_done), win);
+
+  gtk_widget_show (window);
+}
+
+static void
+add_constraint (ConstraintEditorWindow *win)
+{
+  edit_constraint (win, NULL);
+}
+
+static void
+guide_editor_done (GuideEditor            *editor,
+                   GtkConstraintGuide     *guide,
+                   ConstraintEditorWindow *win)
+{
+  gtk_widget_destroy (gtk_widget_get_ancestor (GTK_WIDGET (editor), GTK_TYPE_WINDOW));
+}
+
+static void
+edit_guide (ConstraintEditorWindow *win,
+            GtkConstraintGuide     *guide)
+{
+  GtkWidget *window;
+  GuideEditor *editor;
+
+  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
+  gtk_window_set_resizable (GTK_WINDOW (window), FALSE);
+  gtk_window_set_transient_for (GTK_WINDOW (window), GTK_WINDOW (win));
+  gtk_window_set_title (GTK_WINDOW (window), "Edit Guide");
+
+  editor = guide_editor_new (guide);
+  gtk_container_add (GTK_CONTAINER (window), GTK_WIDGET (editor));
+
+  g_signal_connect (editor, "done", G_CALLBACK (guide_editor_done), win);
+  gtk_widget_show (window);
+}
+
+static void
+row_activated (GtkListBox *list,
+               GtkListBoxRow *row,
+               ConstraintEditorWindow *win)
+{
+  GObject *item;
+
+  item = G_OBJECT (g_object_get_data (G_OBJECT (row), "item"));
+
+  if (GTK_IS_CONSTRAINT (item))
+    edit_constraint (win, GTK_CONSTRAINT (item));
+  else if (GTK_IS_CONSTRAINT_GUIDE (item))
+    edit_guide (win, GTK_CONSTRAINT_GUIDE (item));
+}
+
+static void
+constraint_editor_window_class_init (ConstraintEditorWindowClass *class)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (class);
+  GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (class);
+
+  g_type_ensure (CONSTRAINT_VIEW_TYPE);
+
+  object_class->finalize = constraint_editor_window_finalize;
+
+  gtk_widget_class_set_template_from_resource (widget_class,
+                                               "/org/gtk/gtk4/constraint-editor/constraint-editor-window.ui");
+
+  gtk_widget_class_bind_template_child (widget_class, ConstraintEditorWindow, paned);
+  gtk_widget_class_bind_template_child (widget_class, ConstraintEditorWindow, view);
+  gtk_widget_class_bind_template_child (widget_class, ConstraintEditorWindow, list);
+
+  gtk_widget_class_bind_template_callback (widget_class, open_cb);
+  gtk_widget_class_bind_template_callback (widget_class, save_cb);
+  gtk_widget_class_bind_template_callback (widget_class, add_child);
+  gtk_widget_class_bind_template_callback (widget_class, add_guide);
+  gtk_widget_class_bind_template_callback (widget_class, add_constraint);
+  gtk_widget_class_bind_template_callback (widget_class, row_activated);
+}
+
+static void
+row_edit (GtkButton *button,
+          ConstraintEditorWindow *win)
+{
+  GtkWidget *row;
+  GObject *item;
+
+  row = gtk_widget_get_ancestor (GTK_WIDGET (button), GTK_TYPE_LIST_BOX_ROW);
+  item = (GObject *)g_object_get_data (G_OBJECT (row), "item");
+  if (GTK_IS_CONSTRAINT (item))
+    edit_constraint (win, GTK_CONSTRAINT (item));
+  else if (GTK_IS_CONSTRAINT_GUIDE (item))
+    edit_guide (win, GTK_CONSTRAINT_GUIDE (item));
+}
+
+static void
+mark_constraints_invalid (ConstraintEditorWindow *win,
+                          gpointer                removed)
+{
+  GtkWidget *child;
+  GObject *item;
+
+  for (child = gtk_widget_get_first_child (win->list);
+       child;
+       child = gtk_widget_get_next_sibling (child))
+    {
+      item = (GObject *)g_object_get_data (G_OBJECT (child), "item");
+      if (GTK_IS_CONSTRAINT (item))
+        {
+          GtkConstraint *constraint = GTK_CONSTRAINT (item);
+
+          if (gtk_constraint_get_target (constraint) == (GtkConstraintTarget *)removed ||
+              gtk_constraint_get_source (constraint) == (GtkConstraintTarget *)removed)
+            {
+              GtkWidget *button;
+              button = (GtkWidget *)g_object_get_data (G_OBJECT (child), "edit");
+              gtk_button_set_icon_name (GTK_BUTTON (button), "dialog-warning-symbolic");
+              gtk_widget_set_tooltip_text (button, "Constraint is invalid");
+            }
+        }
+    }
+}
+
+static void
+row_delete (GtkButton *button,
+            ConstraintEditorWindow *win)
+{
+  GtkWidget *row;
+  GObject *item;
+
+  row = gtk_widget_get_ancestor (GTK_WIDGET (button), GTK_TYPE_LIST_BOX_ROW);
+  item = (GObject *)g_object_get_data (G_OBJECT (row), "item");
+  if (GTK_IS_CONSTRAINT (item))
+    constraint_view_remove_constraint (CONSTRAINT_VIEW (win->view),
+                                       GTK_CONSTRAINT (item));
+  else if (GTK_IS_CONSTRAINT_GUIDE (item))
+    {
+      mark_constraints_invalid (win, item);
+      constraint_view_remove_guide (CONSTRAINT_VIEW (win->view),
+                                    GTK_CONSTRAINT_GUIDE (item));
+    }
+  else if (GTK_IS_WIDGET (item))
+    {
+      mark_constraints_invalid (win, item);
+      constraint_view_remove_child (CONSTRAINT_VIEW (win->view),
+                                    GTK_WIDGET (item));
+    }
+}
+
+static GtkWidget *
+create_widget_func (gpointer item,
+                    gpointer user_data)
+{
+  ConstraintEditorWindow *win = user_data;
+  const char *name;
+  char *freeme = NULL;
+  GtkWidget *row, *box, *label, *button;
+
+  if (GTK_IS_WIDGET (item))
+    name = gtk_widget_get_name (GTK_WIDGET (item));
+  else if (GTK_IS_CONSTRAINT_GUIDE (item))
+    name = gtk_constraint_guide_get_name (GTK_CONSTRAINT_GUIDE (item));
+  else if (GTK_IS_CONSTRAINT (item))
+    name = freeme = constraint_editor_constraint_to_string (GTK_CONSTRAINT (item));
+  else
+    name = "";
+
+  row = gtk_list_box_row_new ();
+  g_object_set_data_full (G_OBJECT (row), "item", g_object_ref (item), g_object_unref);
+  box = gtk_box_new (GTK_ORIENTATION_HORIZONTAL, 0);
+  label = gtk_label_new (name);
+  if (GTK_IS_WIDGET (item) || GTK_IS_CONSTRAINT_GUIDE (item))
+    g_object_bind_property (item, "name",
+                            label, "label",
+                            G_BINDING_DEFAULT);
+  g_object_set (label, "margin", 10, NULL);
+  gtk_label_set_xalign (GTK_LABEL (label), 0.0);
+  gtk_widget_set_hexpand (label, TRUE);
+  gtk_container_add (GTK_CONTAINER (row), box);
+  gtk_container_add (GTK_CONTAINER (box), label);
+
+  if (GTK_IS_CONSTRAINT (item) || GTK_IS_CONSTRAINT_GUIDE (item))
+    {
+      button = gtk_button_new_from_icon_name ("document-edit-symbolic");
+      gtk_button_set_relief (GTK_BUTTON (button), GTK_RELIEF_NONE);
+      g_signal_connect (button, "clicked", G_CALLBACK (row_edit), win);
+      g_object_set_data (G_OBJECT (row), "edit", button);
+      gtk_container_add (GTK_CONTAINER (box), button);
+      button = gtk_button_new_from_icon_name ("edit-delete-symbolic");
+      gtk_button_set_relief (GTK_BUTTON (button), GTK_RELIEF_NONE);
+      g_signal_connect (button, "clicked", G_CALLBACK (row_delete), win);
+      gtk_container_add (GTK_CONTAINER (box), button);
+    }
+  else if (GTK_IS_WIDGET (item))
+    {
+      button = gtk_button_new_from_icon_name ("edit-delete-symbolic");
+      gtk_button_set_relief (GTK_BUTTON (button), GTK_RELIEF_NONE);
+      g_signal_connect (button, "clicked", G_CALLBACK (row_delete), win);
+      gtk_container_add (GTK_CONTAINER (box), button);
+    }
+
+  g_free (freeme);
+
+  return row;
+}
+
+static void
+constraint_editor_window_init (ConstraintEditorWindow *self)
+{
+  gtk_widget_init_template (GTK_WIDGET (self));
+
+  gtk_list_box_bind_model (GTK_LIST_BOX (self->list),
+                           constraint_view_get_model (CONSTRAINT_VIEW (self->view)),
+                           create_widget_func,
+                           self,
+                           NULL);
+}
+
+ConstraintEditorWindow *
+constraint_editor_window_new (ConstraintEditorApplication *application)
+{
+  return g_object_new (CONSTRAINT_EDITOR_WINDOW_TYPE,
+                       "application", application,
+                       NULL);
+}

demos/constraint-editor/constraint-editor-window.h

@@ -0,0 +1,34 @@
+/*
+ * Copyright © 2019 Red Hat, Inc
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Authors: Matthias Clasen
+ */
+
+#pragma once
+
+#include <gtk/gtk.h>
+
+#include "constraint-editor-application.h"
+
+
+#define CONSTRAINT_EDITOR_WINDOW_TYPE (constraint_editor_window_get_type ())
+
+G_DECLARE_FINAL_TYPE (ConstraintEditorWindow, constraint_editor_window, CONSTRAINT, EDITOR_WINDOW, GtkApplicationWindow)
+
+ConstraintEditorWindow * constraint_editor_window_new  (ConstraintEditorApplication  *application);
+
+gboolean                 constraint_editor_window_load (ConstraintEditorWindow       *self,
+                                                        GFile                        *file);

demos/constraint-editor/constraint-editor-window.ui

@@ -0,0 +1,82 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<interface>
+  <template class="ConstraintEditorWindow" parent="GtkApplicationWindow">
+    <style>
+      <class name="devel"/>
+    </style>
+    <property name="title" translatable="yes">GTK Constraint Editor</property>
+    <property name="default-width">1024</property>
+    <property name="default-height">768</property>
+    <child type="titlebar">
+      <object class="GtkHeaderBar" id="header">
+        <property name="title" translatable="yes">GTK Constraint Editor</property>
+        <property name="show-title-buttons">1</property>
+        <child type="start">
+          <object class="GtkButton">
+            <property name="icon-name">document-open-symbolic</property>
+            <property name="tooltip-text">Open ui file</property>
+            <signal name="clicked" handler="open_cb"/>
+          </object>
+        </child>
+        <child type="start">
+          <object class="GtkButton">
+            <property name="icon-name">document-save-symbolic</property>
+            <property name="tooltip-text">Save to ui file</property>
+            <signal name="clicked" handler="save_cb"/>
+          </object>
+        </child>
+      </object>
+    </child>
+    <child>
+      <object class="GtkPaned" id="paned">
+        <property name="orientation">horizontal</property>
+        <child>
+          <object class="GtkBox">
+            <property name="orientation">vertical</property>
+            <child>
+              <object class="GtkBox">
+                <property name="orientation">horizontal</property>
+                <child>
+                  <object class="GtkButton">
+                    <property name="label">Add Child</property>
+                    <signal name="clicked" handler="add_child" swapped="yes"/>
+                  </object>
+                </child>
+                <child>
+                  <object class="GtkButton">
+                    <property name="label">Add Guide</property>
+                    <signal name="clicked" handler="add_guide" swapped="yes"/>
+                  </object>
+                </child>
+                <child>
+                  <object class="GtkButton">
+                    <property name="label">Add Constraint</property>
+                    <signal name="clicked" handler="add_constraint" swapped="yes"/>
+                  </object>
+                </child>
+              </object>
+            </child>
+            <child>
+              <object class="GtkScrolledWindow">
+                <property name="hscrollbar-policy">never</property>
+                <property name="vscrollbar-policy">automatic</property>
+                <property name="vexpand">1</property>
+                <child>
+                  <object class="GtkListBox" id="list">
+                    <property name="show-separators">1</property>
+                    <property name="selection-mode">none</property>
+                    <signal name="row-activated" handler="row_activated"/>
+                  </object>
+                </child>
+              </object>
+            </child>
+          </object>
+        </child>
+        <child>
+          <object class="ConstraintView" id="view">
+          </object>
+        </child>
+      </object>
+    </child>
+  </template>
+</interface>

demos/constraint-editor/constraint-editor.c

@@ -0,0 +1,656 @@
+/*
+ * Copyright © 2019 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Authors: Matthias Clasen
+ */
+
+#include "config.h"
+
+#include "constraint-editor.h"
+
+struct _ConstraintEditor
+{
+  GtkWidget parent_instance;
+
+  GtkWidget *grid;
+  GtkWidget *target;
+  GtkWidget *target_attr;
+  GtkWidget *relation;
+  GtkWidget *source;
+  GtkWidget *source_attr;
+  GtkWidget *multiplier;
+  GtkWidget *constant;
+  GtkWidget *strength;
+  GtkWidget *preview;
+  GtkWidget *button;
+
+  GtkConstraint *constraint;
+  GListModel *model;
+
+  gboolean constructed;
+};
+
+enum {
+  PROP_MODEL = 1,
+  PROP_CONSTRAINT,
+  LAST_PROP
+};
+
+static GParamSpec *pspecs[LAST_PROP];
+
+enum {
+  DONE,
+  LAST_SIGNAL
+};
+
+static guint signals[LAST_SIGNAL];
+
+G_DEFINE_TYPE(ConstraintEditor, constraint_editor, GTK_TYPE_WIDGET);
+
+static const char *
+get_target_name (GtkConstraintTarget *target)
+{
+  if (target == NULL)
+    return "super";
+  else if (GTK_IS_WIDGET (target))
+    return gtk_widget_get_name (GTK_WIDGET (target));
+  else if (GTK_IS_CONSTRAINT_GUIDE (target))
+    return gtk_constraint_guide_get_name (GTK_CONSTRAINT_GUIDE (target));
+  else
+    return "";
+}
+
+static void
+constraint_target_combo (GListModel *model,
+                         GtkWidget  *combo,
+                         gboolean    is_source)
+{
+  int i;
+
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "super", "Super");
+
+  if (model)
+    {
+      for (i = 0; i < g_list_model_get_n_items (model); i++)
+        {
+          GObject *item = g_list_model_get_object (model, i);
+          const char *name;
+
+          if (GTK_IS_CONSTRAINT (item))
+            continue;
+
+          name = get_target_name (GTK_CONSTRAINT_TARGET (item));
+
+          gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), name, name);
+          g_object_unref (item);
+        }
+    }
+}
+
+static void
+constraint_attribute_combo (GtkWidget *combo,
+                            gboolean is_source)
+{
+  if (is_source)
+    gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "none", "None");
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "left", "Left");
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "right", "Right");
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "top", "Top");
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "bottom", "Bottom");
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "start", "Start");
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "end", "End");
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "width", "Width");
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "height", "Height");
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "center-x", "Center X");
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "center-y", "Center Y");
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "baseline", "Baseline");
+}
+
+static void
+constraint_relation_combo (GtkWidget *combo)
+{
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "le", "≤");
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "eq", "=");
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "ge", "≥");
+}
+
+static void
+constraint_strength_combo (GtkWidget *combo)
+{
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "weak", "Weak");
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "medium", "Medium");
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "strong", "Strong");
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "required", "Required");
+}
+
+static gpointer
+get_target (GListModel *model,
+            const char *id)
+{
+  int i;
+
+  if (strcmp ("super", id) == 0)
+    return NULL;
+
+  for (i = 0; i < g_list_model_get_n_items (model); i++)
+    {
+      GObject *item = g_list_model_get_object (model, i);
+      g_object_unref (item);
+      if (GTK_IS_CONSTRAINT (item))
+        continue;
+      else if (GTK_IS_WIDGET (item))
+        {
+          if (strcmp (id, gtk_widget_get_name (GTK_WIDGET (item))) == 0)
+            return item;
+        }
+      else if (GTK_IS_CONSTRAINT_GUIDE (item))
+        {
+          if (strcmp (id, gtk_constraint_guide_get_name (GTK_CONSTRAINT_GUIDE (item))) == 0)
+            return item;
+        }
+    }
+
+  return NULL;
+}
+
+static GtkConstraintAttribute
+get_target_attr (const char *id)
+{
+  GtkConstraintAttribute attr;
+  GEnumClass *class = g_type_class_ref (GTK_TYPE_CONSTRAINT_ATTRIBUTE);
+  GEnumValue *value = g_enum_get_value_by_nick (class, id);
+  attr = value->value;
+  g_type_class_unref (class);
+
+  return attr;
+}
+
+static const char *
+get_attr_nick (GtkConstraintAttribute attr)
+{
+  GEnumClass *class = g_type_class_ref (GTK_TYPE_CONSTRAINT_ATTRIBUTE);
+  GEnumValue *value = g_enum_get_value (class, attr);
+  const char *nick = value->value_nick;
+  g_type_class_unref (class);
+
+  return nick;
+}
+
+static GtkConstraintRelation
+get_relation (const char *id)
+{
+  GtkConstraintRelation relation;
+  GEnumClass *class = g_type_class_ref (GTK_TYPE_CONSTRAINT_RELATION);
+  GEnumValue *value = g_enum_get_value_by_nick (class, id);
+  relation = value->value;
+  g_type_class_unref (class);
+
+  return relation;
+}
+
+static const char *
+get_relation_nick (GtkConstraintRelation relation)
+{
+  GEnumClass *class = g_type_class_ref (GTK_TYPE_CONSTRAINT_RELATION);
+  GEnumValue *value = g_enum_get_value (class, relation);
+  const char *nick = value->value_nick;
+  g_type_class_unref (class);
+
+  return nick;
+}
+
+static GtkConstraintStrength
+get_strength (const char *id)
+{
+  GtkConstraintStrength strength;
+  GEnumClass *class = g_type_class_ref (GTK_TYPE_CONSTRAINT_STRENGTH);
+  GEnumValue *value = g_enum_get_value_by_nick (class, id);
+  strength = value->value;
+  g_type_class_unref (class);
+
+  return strength;
+}
+
+static const char *
+get_strength_nick (GtkConstraintStrength strength)
+{
+  GEnumClass *class = g_type_class_ref (GTK_TYPE_CONSTRAINT_STRENGTH);
+  GEnumValue *value = g_enum_get_value (class, strength);
+  const char *nick = value->value_nick;
+  g_type_class_unref (class);
+
+  return nick;
+}
+
+void
+constraint_editor_serialize_constraint (GString       *str,
+                                        int            indent,
+                                        GtkConstraint *constraint)
+{
+  const char *target;
+  const char *target_attr;
+  const char *relation;
+  const char *source;
+  const char *source_attr;
+  double multiplier;
+  double constant;
+  const char *strength;
+
+  target = get_target_name (gtk_constraint_get_target (constraint));
+  target_attr = get_attr_nick (gtk_constraint_get_target_attribute (constraint));
+  relation = get_relation_nick (gtk_constraint_get_relation (constraint));
+  source = get_target_name (gtk_constraint_get_source (constraint));
+  source_attr = get_attr_nick (gtk_constraint_get_source_attribute (constraint));
+  multiplier = gtk_constraint_get_multiplier (constraint);
+  constant = gtk_constraint_get_constant (constraint);
+  strength = get_strength_nick (gtk_constraint_get_strength (constraint));
+
+  g_string_append_printf (str, "%*s<constraint target=\"%s\" target-attribute=\"%s\"\n", indent, "", target, target_attr);
+  g_string_append_printf (str, "%*s            relation=\"%s\"\n", indent, "", relation);
+  if (strcmp (source_attr, "none") != 0)
+    {
+      g_string_append_printf (str, "%*s            source=\"%s\" source-attribute=\"%s\"\n", indent, "", source, source_attr);
+      g_string_append_printf (str, "%*s            multiplier=\"%g\"\n", indent, "", multiplier);
+    }
+  g_string_append_printf (str, "%*s            constant=\"%g\"\n", indent, "", constant);
+  g_string_append_printf (str, "%*s            strength=\"%s\" />\n", indent, "", strength);
+}
+
+static void
+create_constraint (GtkButton        *button,
+                   ConstraintEditor *editor)
+{
+  const char *id;
+  gpointer target;
+  GtkConstraintAttribute target_attr;
+  gpointer source;
+  GtkConstraintAttribute source_attr;
+  GtkConstraintRelation relation;
+  double multiplier;
+  double constant;
+  int strength;
+  GtkConstraint *constraint;
+
+  id = gtk_combo_box_get_active_id (GTK_COMBO_BOX (editor->target));
+  target = get_target (editor->model, id);
+  id = gtk_combo_box_get_active_id (GTK_COMBO_BOX (editor->target_attr));
+  target_attr = get_target_attr (id);
+
+  id = gtk_combo_box_get_active_id (GTK_COMBO_BOX (editor->source));
+  source = get_target (editor->model, id);
+  id = gtk_combo_box_get_active_id (GTK_COMBO_BOX (editor->source_attr));
+  source_attr = get_target_attr (id);
+
+  id = gtk_combo_box_get_active_id (GTK_COMBO_BOX (editor->relation));
+  relation = get_relation (id);
+
+  multiplier = g_ascii_strtod (gtk_editable_get_text (GTK_EDITABLE (editor->multiplier)), NULL);
+
+  constant = g_ascii_strtod (gtk_editable_get_text (GTK_EDITABLE (editor->constant)), NULL);
+
+  id = gtk_combo_box_get_active_id (GTK_COMBO_BOX (editor->strength));
+  strength = get_strength (id);
+
+  constraint = gtk_constraint_new (target, target_attr,
+                                   relation,
+                                   source, source_attr,
+                                   multiplier,
+                                   constant,
+                                   strength);
+  g_signal_emit (editor, signals[DONE], 0, constraint);
+  g_object_unref (constraint);
+}
+
+static void
+source_attr_changed (ConstraintEditor *editor)
+{
+  const char *id;
+
+  id = gtk_combo_box_get_active_id (GTK_COMBO_BOX (editor->source_attr));
+  if (strcmp (id, "none") == 0)
+    {
+      gtk_combo_box_set_active (GTK_COMBO_BOX (editor->source), -1);
+      gtk_editable_set_text (GTK_EDITABLE (editor->multiplier), "");
+      gtk_widget_set_sensitive (editor->source, FALSE);
+      gtk_widget_set_sensitive (editor->multiplier, FALSE);
+    }
+  else
+    {
+      gtk_widget_set_sensitive (editor->source, TRUE);
+      gtk_widget_set_sensitive (editor->multiplier, TRUE);
+    }
+}
+
+char *
+constraint_editor_constraint_to_string (GtkConstraint *constraint)
+{
+  GString *str;
+  const char *name;
+  const char *attr;
+  const char *relation;
+  double c, m;
+
+  str = g_string_new ("");
+
+  name = get_target_name (gtk_constraint_get_target (constraint));
+  attr = get_attr_nick (gtk_constraint_get_target_attribute (constraint));
+  relation = get_relation_nick (gtk_constraint_get_relation (constraint));
+
+  if (name == NULL)
+    name = "[ ]";
+
+  g_string_append_printf (str, "%s.%s %s ", name, attr, relation);
+
+  c = gtk_constraint_get_constant (constraint);
+
+  attr = get_attr_nick (gtk_constraint_get_source_attribute (constraint));
+  if (strcmp (attr, "none") != 0)
+    {
+      name = get_target_name (gtk_constraint_get_source (constraint));
+      m = gtk_constraint_get_multiplier (constraint);
+
+      if (name == NULL)
+        name = "[ ]";
+
+      g_string_append_printf (str, "%s.%s", name, attr);
+
+      if (m != 1.0)
+        g_string_append_printf (str, " × %g", m);
+
+      if (c > 0.0)
+        g_string_append_printf (str, " + %g", c);
+      else if (c < 0.0)
+        g_string_append_printf (str, " - %g", -c);
+    }
+  else
+    g_string_append_printf (str, "%g", c);
+
+  return g_string_free (str, FALSE);
+}
+
+static void
+update_preview (ConstraintEditor *editor)
+{
+  GString *str;
+  const char *name;
+  const char *attr;
+  char *relation;
+  const char *multiplier;
+  const char *constant;
+  double c, m;
+
+  if (!editor->constructed)
+    return;
+
+  str = g_string_new ("");
+
+  name = gtk_combo_box_get_active_id (GTK_COMBO_BOX (editor->target));
+  attr = gtk_combo_box_get_active_id (GTK_COMBO_BOX (editor->target_attr));
+  relation = gtk_combo_box_text_get_active_text (GTK_COMBO_BOX_TEXT (editor->relation));
+
+  if (name == NULL)
+    name = "[ ]";
+
+  g_string_append_printf (str, "%s.%s %s ", name, attr, relation);
+  g_free (relation);
+
+  constant = gtk_editable_get_text (GTK_EDITABLE (editor->constant));
+  c = g_ascii_strtod (constant, NULL);
+
+  attr = gtk_combo_box_get_active_id (GTK_COMBO_BOX (editor->source_attr));
+  if (strcmp (attr, "none") != 0)
+    {
+      name = gtk_combo_box_get_active_id (GTK_COMBO_BOX (editor->source));
+      multiplier = gtk_editable_get_text (GTK_EDITABLE (editor->multiplier));
+      m = g_ascii_strtod (multiplier, NULL);
+
+      if (name == NULL)
+        name = "[ ]";
+
+      g_string_append_printf (str, "%s.%s", name, attr);
+
+      if (m != 1.0)
+        g_string_append_printf (str, " × %g", m);
+
+      if (c > 0.0)
+        g_string_append_printf (str, " + %g", c);
+      else if (c < 0.0)
+        g_string_append_printf (str, " - %g", -c);
+    }
+  else
+    g_string_append_printf (str, "%g", c);
+
+  gtk_label_set_label (GTK_LABEL (editor->preview), str->str);
+
+  g_string_free (str, TRUE);
+}
+
+static void
+update_button (ConstraintEditor *editor)
+{
+  if (gtk_combo_box_get_active_id (GTK_COMBO_BOX (editor->target)) != NULL &&
+      gtk_combo_box_get_active_id (GTK_COMBO_BOX (editor->source)) != NULL)
+    gtk_widget_set_sensitive (editor->button, TRUE);
+  else
+    gtk_widget_set_sensitive (editor->button, FALSE);
+}
+
+static void
+constraint_editor_init (ConstraintEditor *editor)
+{
+  gtk_widget_init_template (GTK_WIDGET (editor));
+}
+
+static void
+constraint_editor_constructed (GObject *object)
+{
+  ConstraintEditor *editor = CONSTRAINT_EDITOR (object);
+
+  constraint_target_combo (editor->model, editor->target, FALSE);
+  constraint_attribute_combo (editor->target_attr, FALSE);
+  constraint_relation_combo (editor->relation);
+  constraint_target_combo (editor->model, editor->source, TRUE);
+  constraint_attribute_combo (editor->source_attr, TRUE);
+
+  constraint_strength_combo (editor->strength);
+
+  if (editor->constraint)
+    {
+      GtkConstraintTarget *target;
+      GtkConstraintAttribute attr;
+      GtkConstraintRelation relation;
+      GtkConstraintStrength strength;
+      const char *nick;
+      char *val;
+      double multiplier;
+      double constant;
+
+      target = gtk_constraint_get_target (editor->constraint);
+      nick = get_target_name (target);
+      gtk_combo_box_set_active_id (GTK_COMBO_BOX (editor->target), nick);
+
+      attr = gtk_constraint_get_target_attribute (editor->constraint);
+      nick = get_attr_nick (attr);
+      gtk_combo_box_set_active_id (GTK_COMBO_BOX (editor->target_attr), nick);
+
+      target = gtk_constraint_get_source (editor->constraint);
+      nick = get_target_name (target);
+      gtk_combo_box_set_active_id (GTK_COMBO_BOX (editor->source), nick);
+
+      attr = gtk_constraint_get_source_attribute (editor->constraint);
+      nick = get_attr_nick (attr);
+      gtk_combo_box_set_active_id (GTK_COMBO_BOX (editor->source_attr), nick);
+
+      relation = gtk_constraint_get_relation (editor->constraint);
+      nick = get_relation_nick (relation);
+      gtk_combo_box_set_active_id (GTK_COMBO_BOX (editor->relation), nick);
+
+      multiplier = gtk_constraint_get_multiplier (editor->constraint);
+      val = g_strdup_printf ("%g", multiplier);
+      gtk_editable_set_text (GTK_EDITABLE (editor->multiplier), val);
+      g_free (val);
+
+      constant = gtk_constraint_get_constant (editor->constraint);
+      val = g_strdup_printf ("%g", constant);
+      gtk_editable_set_text (GTK_EDITABLE (editor->constant), val);
+      g_free (val);
+
+      strength = gtk_constraint_get_strength (editor->constraint);
+      nick = get_strength_nick (strength);
+      gtk_combo_box_set_active_id (GTK_COMBO_BOX (editor->strength), nick);
+
+      gtk_button_set_label (GTK_BUTTON (editor->button), "Apply");
+    }
+  else
+    {
+      gtk_combo_box_set_active_id (GTK_COMBO_BOX (editor->target_attr), "left");
+      gtk_combo_box_set_active_id (GTK_COMBO_BOX (editor->source_attr), "left");
+      gtk_combo_box_set_active_id (GTK_COMBO_BOX (editor->relation), "eq");
+      gtk_combo_box_set_active_id (GTK_COMBO_BOX (editor->strength), "required");
+
+      gtk_editable_set_text (GTK_EDITABLE (editor->multiplier), "1.0");
+      gtk_editable_set_text (GTK_EDITABLE (editor->constant), "0.0");
+
+      gtk_button_set_label (GTK_BUTTON (editor->button), "Create");
+    }
+
+  editor->constructed = TRUE;
+  update_preview (editor);
+  update_button (editor);
+}
+
+static void
+constraint_editor_set_property (GObject      *object,
+                                guint         property_id,
+                                const GValue *value,
+                                GParamSpec   *pspec)
+{
+  ConstraintEditor *self = CONSTRAINT_EDITOR (object);
+
+  switch (property_id)
+    {
+    case PROP_MODEL:
+      self->model = g_value_dup_object (value);
+      break;
+
+    case PROP_CONSTRAINT:
+      self->constraint = g_value_dup_object (value);
+      break;
+
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
+    }
+}
+
+static void
+constraint_editor_get_property (GObject    *object,
+                                guint       property_id,
+                                GValue     *value,
+                                GParamSpec *pspec)
+{
+  ConstraintEditor *self = CONSTRAINT_EDITOR (object);
+
+  switch (property_id)
+    {
+    case PROP_MODEL:
+      g_value_set_object (value, self->model);
+      break;
+
+    case PROP_CONSTRAINT:
+      g_value_set_object (value, self->constraint);
+      break;
+
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
+    }
+}
+
+static void
+constraint_editor_dispose (GObject *object)
+{
+  ConstraintEditor *self = (ConstraintEditor *)object;
+
+  g_clear_pointer (&self->grid, gtk_widget_unparent);
+  g_clear_object (&self->model);
+  g_clear_object (&self->constraint);
+
+  G_OBJECT_CLASS (constraint_editor_parent_class)->dispose (object);
+}
+
+static void
+constraint_editor_class_init (ConstraintEditorClass *class)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (class);
+  GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (class);
+
+  object_class->constructed = constraint_editor_constructed;
+  object_class->dispose = constraint_editor_dispose;
+  object_class->set_property = constraint_editor_set_property;
+  object_class->get_property = constraint_editor_get_property;
+
+  pspecs[PROP_CONSTRAINT] =
+    g_param_spec_object ("constraint", "constraint", "constraint",
+                         GTK_TYPE_CONSTRAINT,
+                         G_PARAM_READWRITE|G_PARAM_CONSTRUCT_ONLY);
+
+  pspecs[PROP_MODEL] =
+    g_param_spec_object ("model", "model", "model",
+                         G_TYPE_LIST_MODEL,
+                         G_PARAM_READWRITE|G_PARAM_CONSTRUCT_ONLY);
+
+  g_object_class_install_properties (object_class, LAST_PROP, pspecs);
+
+  signals[DONE] =
+    g_signal_new ("done",
+                  G_TYPE_FROM_CLASS (object_class),
+                  G_SIGNAL_RUN_LAST,
+                  0,
+                  NULL, NULL,
+                  NULL,
+                  G_TYPE_NONE, 1, GTK_TYPE_CONSTRAINT);
+
+  gtk_widget_class_set_layout_manager_type (widget_class, GTK_TYPE_BIN_LAYOUT);
+
+  gtk_widget_class_set_template_from_resource (widget_class,
+                                               "/org/gtk/gtk4/constraint-editor/constraint-editor.ui");
+
+  gtk_widget_class_bind_template_child (widget_class, ConstraintEditor, grid);
+  gtk_widget_class_bind_template_child (widget_class, ConstraintEditor, target);
+  gtk_widget_class_bind_template_child (widget_class, ConstraintEditor, target_attr);
+  gtk_widget_class_bind_template_child (widget_class, ConstraintEditor, relation);
+  gtk_widget_class_bind_template_child (widget_class, ConstraintEditor, source);
+  gtk_widget_class_bind_template_child (widget_class, ConstraintEditor, source_attr);
+  gtk_widget_class_bind_template_child (widget_class, ConstraintEditor, multiplier);
+  gtk_widget_class_bind_template_child (widget_class, ConstraintEditor, constant);
+  gtk_widget_class_bind_template_child (widget_class, ConstraintEditor, strength);
+  gtk_widget_class_bind_template_child (widget_class, ConstraintEditor, preview);
+  gtk_widget_class_bind_template_child (widget_class, ConstraintEditor, button);
+
+  gtk_widget_class_bind_template_callback (widget_class, update_preview);
+  gtk_widget_class_bind_template_callback (widget_class, update_button);
+  gtk_widget_class_bind_template_callback (widget_class, create_constraint);
+  gtk_widget_class_bind_template_callback (widget_class, source_attr_changed);
+}
+
+ConstraintEditor *
+constraint_editor_new (GListModel    *model,
+                       GtkConstraint *constraint)
+{
+  return g_object_new (CONSTRAINT_EDITOR_TYPE,
+                       "model", model,
+                       "constraint", constraint,
+                       NULL);
+}

demos/constraint-editor/constraint-editor.css

@@ -0,0 +1,12 @@
+constraintview {
+  background: black;
+  color: white;
+}
+
+constraintview .child {
+  background: red;
+}
+
+constraintview .guide {
+  background: blue;
+}

demos/constraint-editor/constraint-editor.gresource.xml

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<gresources>
+  <gresource prefix="/org/gtk/gtk4/constraint-editor">
+    <file preprocess="xml-stripblanks">constraint-editor-window.ui</file>
+    <file preprocess="xml-stripblanks">constraint-editor.ui</file>
+    <file preprocess="xml-stripblanks">guide-editor.ui</file>
+    <file>constraint-editor.css</file>
+  </gresource>
+</gresources>

demos/constraint-editor/constraint-editor.h

@@ -0,0 +1,34 @@
+/*
+ * Copyright © 2019 Red Hat, Inc
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Authors: Matthias Clasen
+ */
+
+#pragma once
+
+#include <gtk/gtk.h>
+
+#define CONSTRAINT_EDITOR_TYPE (constraint_editor_get_type ())
+
+G_DECLARE_FINAL_TYPE (ConstraintEditor, constraint_editor, CONSTRAINT, EDITOR, GtkWidget)
+
+ConstraintEditor * constraint_editor_new (GListModel    *model,
+                                          GtkConstraint *constraint);
+
+void constraint_editor_serialize_constraint (GString       *str,
+                                             int            indent,
+                                             GtkConstraint *constraint);
+char *constraint_editor_constraint_to_string (GtkConstraint *constraint);

demos/constraint-editor/constraint-editor.ui

@@ -0,0 +1,163 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<interface>
+  <template class="ConstraintEditor" parent="GtkWidget">
+    <child>
+      <object class="GtkGrid" id="grid">
+        <property name="margin">20</property>
+        <property name="row-spacing">10</property>
+        <property name="column-spacing">10</property>
+        <child>
+          <object class="GtkLabel">
+            <property name="label">Target</property>
+            <layout>
+              <property name="left-attach">0</property>
+              <property name="top-attach">1</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkComboBoxText" id="target">
+            <signal name="changed" handler="update_preview" swapped="yes"/>
+            <signal name="changed" handler="update_button" swapped="yes"/>
+            <layout>
+              <property name="left-attach">1</property>
+              <property name="top-attach">1</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkComboBoxText" id="target_attr">
+            <signal name="changed" handler="update_preview" swapped="yes"/>
+            <layout>
+              <property name="left-attach">2</property>
+              <property name="top-attach">1</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkLabel">
+            <property name="label">Relation</property>
+            <layout>
+              <property name="left-attach">0</property>
+              <property name="top-attach">2</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkComboBoxText" id="relation">
+            <signal name="changed" handler="update_preview" swapped="yes"/>
+            <layout>
+              <property name="left-attach">1</property>
+              <property name="top-attach">2</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkLabel">
+            <property name="label">Source</property>
+            <layout>
+              <property name="left-attach">0</property>
+              <property name="top-attach">3</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkComboBoxText" id="source">
+            <signal name="changed" handler="update_preview" swapped="yes"/>
+            <signal name="changed" handler="update_button" swapped="yes"/>
+            <layout>
+              <property name="left-attach">1</property>
+              <property name="top-attach">3</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkComboBoxText" id="source_attr">
+            <signal name="changed" handler="update_preview" swapped="yes"/>
+            <signal name="changed" handler="source_attr_changed" swapped="yes"/>
+            <layout>
+              <property name="left-attach">2</property>
+              <property name="top-attach">3</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkLabel">
+            <property name="label">Multiplier</property>
+            <layout>
+              <property name="left-attach">0</property>
+              <property name="top-attach">4</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkEntry" id="multiplier">
+            <signal name="changed" handler="update_preview" swapped="yes"/>
+            <layout>
+              <property name="left-attach">1</property>
+              <property name="top-attach">4</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkLabel">
+            <property name="label">Constant</property>
+            <layout>
+              <property name="left-attach">0</property>
+              <property name="top-attach">5</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkEntry" id="constant">
+            <signal name="changed" handler="update_preview" swapped="yes"/>
+            <layout>
+              <property name="left-attach">1</property>
+              <property name="top-attach">5</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkLabel">
+            <property name="label">Strength</property>
+            <layout>
+              <property name="left-attach">0</property>
+              <property name="top-attach">6</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkComboBoxText" id="strength">
+            <layout>
+              <property name="left-attach">1</property>
+              <property name="top-attach">6</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkLabel" id="preview">
+            <property name="xalign">0</property>
+            <layout>
+              <property name="left-attach">1</property>
+              <property name="top-attach">7</property>
+              <property name="column-span">2</property>
+            </layout>
+            <attributes>
+              <attribute name="scale" value="1.44"/>
+            </attributes>
+          </object>
+        </child>
+        <child>
+          <object class="GtkButton" id="button">
+            <property name="label">Create</property>
+            <signal name="clicked" handler="create_constraint"/>
+            <layout>
+              <property name="left-attach">2</property>
+              <property name="top-attach">8</property>
+            </layout>
+          </object>
+        </child>
+      </object>
+    </child>
+  </template>
+</interface>

demos/constraint-editor/constraint-view-child.c

@@ -0,0 +1,93 @@
+/*
+ * Copyright © 2019 Red Hat, Inc
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Authors: Matthias Clasen
+ */
+
+#include "constraint-view-child.h"
+
+struct _ConstraintViewChild
+{
+  GObject parent_instance;
+
+  char *name;
+};
+
+enum {
+  PROP_NAME = 1,
+  LAST_PROP
+};
+
+static GParamSpec props[LAST_PROP];
+
+G_DEFINE_TYPE (ConstraintViewChild, constraint_view_child, G_TYPE_OBJECT)
+
+static void
+constraint_view_child_init (ConstraintViewChild *child)
+{
+}
+
+static void
+constraint_view_child_finalize (GObject *object)
+{
+  ConstraintViewChild *child = CONSTRAINT_VIEW_CHILD (object);
+
+  g_free (child->name);
+
+  G_OBJECT_CLASS (constraint_view_child_parent_class)->finalize (object);
+}
+
+static void
+constraint_view_child_set_property (GObject *object,
+                                    
+static void
+constraint_view_child_class_init (ConstraintViewChildClass *class)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (class);
+
+  object_class->finalize = constraint_view_child_finalize;
+  object_class->get_property = constraint_view_child_get_property;
+  object_class->set_property = constraint_view_child_set_property;
+
+  props[PROP_NAME] =
+    g_param_spec_string ("name", "name", "name",
+                         NULL,
+                         G_PARAM_READWRITE);
+
+  g_object_class_install_properties (object_class, LAST_PROP, props);
+}
+
+#define CONSTRAINT_VIEW_CHILD_TYPE (constraint_view_get_type ())
+
+G_DECLARE_TYPE (ConstraintViewChild, constraint_view_child, CONSTRAINT, VIEW_CHILD, GObject)
+
+#define CONSTRAINT_VIEW_WIDGET_TYPE (constraint_view_widget_get_type ())
+
+G_DECLARE_FINAL_TYPE (ConstraintViewWidget, constraint_view_widget, CONSTRAINT, VIEW_WIDGET, ConstraintViewChild)
+
+ConstraintViewWidget * constraint_view_widget_new (void);
+
+#define CONSTRAINT_VIEW_GUIDE_TYPE (constraint_view_guide_get_type ())
+
+G_DECLARE_FINAL_TYPE (ConstraintViewGuide, constraint_view_guide, CONSTRAINT, VIEW_GUIDE, ConstraintViewChild)
+
+ConstraintViewGuide * constraint_view_guide_new (void);
+
+#define CONSTRAINT_VIEW_CONSTRAINT_TYPE (constraint_view_constraint_get_type ())
+
+G_DECLARE_FINAL_TYPE (ConstraintViewConstraint, constraint_view_constraint, CONSTRAINT, VIEW_CONSTRAINT, ConstraintViewChild)
+
+ConstraintViewGuide * constraint_view_constraint_new (void);

demos/constraint-editor/constraint-view-child.h

@@ -0,0 +1,44 @@
+/*
+ * Copyright © 2019 Red Hat, Inc
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Authors: Matthias Clasen
+ */
+
+#pragma once
+
+#include <gtk/gtk.h>
+
+#define CONSTRAINT_VIEW_CHILD_TYPE (constraint_view_get_type ())
+
+G_DECLARE_TYPE (ConstraintViewChild, constraint_view_child, CONSTRAINT, VIEW_CHILD, GObject)
+
+#define CONSTRAINT_VIEW_WIDGET_TYPE (constraint_view_widget_get_type ())
+
+G_DECLARE_FINAL_TYPE (ConstraintViewWidget, constraint_view_widget, CONSTRAINT, VIEW_WIDGET, ConstraintViewChild)
+
+ConstraintViewWidget * constraint_view_widget_new (void);
+
+#define CONSTRAINT_VIEW_GUIDE_TYPE (constraint_view_guide_get_type ())
+
+G_DECLARE_FINAL_TYPE (ConstraintViewGuide, constraint_view_guide, CONSTRAINT, VIEW_GUIDE, ConstraintViewChild)
+
+ConstraintViewGuide * constraint_view_guide_new (void);
+
+#define CONSTRAINT_VIEW_CONSTRAINT_TYPE (constraint_view_constraint_get_type ())
+
+G_DECLARE_FINAL_TYPE (ConstraintViewConstraint, constraint_view_constraint, CONSTRAINT, VIEW_CONSTRAINT, ConstraintViewChild)
+
+ConstraintViewGuide * constraint_view_constraint_new (void);

demos/constraint-editor/constraint-view.c

@@ -0,0 +1,343 @@
+/* Copyright (C) 2019 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <gtk/gtk.h>
+#include "constraint-view.h"
+
+struct _ConstraintView
+{
+  GtkWidget parent;
+
+  GListModel *model;
+
+  GtkWidget *drag_widget;
+};
+
+G_DEFINE_TYPE (ConstraintView, constraint_view, GTK_TYPE_WIDGET);
+
+static void
+constraint_view_dispose (GObject *object)
+{
+  ConstraintView *view = CONSTRAINT_VIEW (object);
+  GtkWidget *child;
+
+  while ((child = gtk_widget_get_first_child (GTK_WIDGET (view))) != NULL)
+    gtk_widget_unparent (child);
+
+  g_clear_object (&view->model);
+
+  G_OBJECT_CLASS (constraint_view_parent_class)->dispose (object);
+}
+
+static void
+constraint_view_class_init (ConstraintViewClass *klass)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (klass);
+  GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (klass);
+
+  object_class->dispose = constraint_view_dispose;
+
+  gtk_widget_class_set_css_name (widget_class, "constraintview");
+}
+
+static void
+update_weak_position (ConstraintView *self,
+                      GtkWidget      *child,
+                      double          x,
+                      double          y)
+{
+  GtkLayoutManager *manager;
+  GtkConstraint *constraint;
+
+  manager = gtk_widget_get_layout_manager (GTK_WIDGET (self));
+  constraint = (GtkConstraint *)g_object_get_data (G_OBJECT (child), "x-constraint");
+  if (constraint)
+    {
+      gtk_constraint_layout_remove_constraint (GTK_CONSTRAINT_LAYOUT (manager),
+                                               constraint);
+      g_object_set_data (G_OBJECT (child), "x-constraint", NULL);
+    }
+  if (x != -100)
+    {
+      constraint = gtk_constraint_new_constant (child,
+                                                GTK_CONSTRAINT_ATTRIBUTE_CENTER_X,
+                                                GTK_CONSTRAINT_RELATION_EQ,
+                                                x,
+                                                GTK_CONSTRAINT_STRENGTH_WEAK);
+      g_object_set_data (G_OBJECT (constraint), "internal", "yes");
+      gtk_constraint_layout_add_constraint (GTK_CONSTRAINT_LAYOUT (manager),
+                                            constraint);
+      g_object_set_data (G_OBJECT (child), "x-constraint", constraint);
+    }
+
+  constraint = (GtkConstraint *)g_object_get_data (G_OBJECT (child), "y-constraint");
+  if (constraint)
+    {
+      gtk_constraint_layout_remove_constraint (GTK_CONSTRAINT_LAYOUT (manager),
+                                                   constraint);
+      g_object_set_data (G_OBJECT (child), "y-constraint", NULL);
+    }
+  if (y != -100)
+    {
+      constraint = gtk_constraint_new_constant (child,
+                                                GTK_CONSTRAINT_ATTRIBUTE_CENTER_Y,
+                                                GTK_CONSTRAINT_RELATION_EQ,
+                                                y,
+                                                GTK_CONSTRAINT_STRENGTH_WEAK);
+      g_object_set_data (G_OBJECT (constraint), "internal", "yes");
+      gtk_constraint_layout_add_constraint (GTK_CONSTRAINT_LAYOUT (manager),
+                                            constraint);
+      g_object_set_data (G_OBJECT (child), "y-constraint", constraint);
+    }
+}
+
+static void
+drag_begin (GtkGestureDrag *drag,
+            double          start_x,
+            double          start_y,
+            ConstraintView *self)
+{
+  GtkWidget *widget;
+
+  widget = gtk_widget_pick (GTK_WIDGET (self), start_x, start_y, GTK_PICK_DEFAULT);
+
+  if (GTK_IS_LABEL (widget))
+    {
+      widget = gtk_widget_get_ancestor (widget, GTK_TYPE_FRAME);
+      if (widget &&
+          gtk_widget_get_parent (widget) == (GtkWidget *)self)
+        {
+          self->drag_widget = widget;
+        }
+    }
+}
+
+static void
+drag_update (GtkGestureDrag *drag,
+             double          offset_x,
+             double          offset_y,
+             ConstraintView *self)
+{
+  double x, y;
+
+  if (!self->drag_widget)
+    return;
+
+  gtk_gesture_drag_get_start_point (drag, &x, &y);
+  update_weak_position (self, self->drag_widget, x + offset_x, y + offset_y);
+}
+
+static void
+drag_end (GtkGestureDrag *drag,
+          double          offset_x,
+          double          offset_y,
+          ConstraintView *self)
+{
+  self->drag_widget = NULL;
+}
+
+static gboolean
+omit_internal (gpointer item, gpointer user_data)
+{
+  if (g_object_get_data (G_OBJECT (item), "internal"))
+    return FALSE;
+
+  return TRUE;
+}
+
+static void
+constraint_view_init (ConstraintView *self)
+{
+  GtkLayoutManager *manager;
+  GtkEventController *controller;
+  GListStore *list;
+  GListModel *all_children;
+  GListModel *all_constraints;
+  GListModel *guides;
+  GListModel *children;
+  GListModel *constraints;
+
+  manager = gtk_constraint_layout_new ();
+  gtk_widget_set_layout_manager (GTK_WIDGET (self), manager);
+
+  all_children = gtk_widget_observe_children (GTK_WIDGET (self));
+  all_constraints = gtk_constraint_layout_observe_constraints (GTK_CONSTRAINT_LAYOUT (manager));
+  guides = gtk_constraint_layout_observe_guides (GTK_CONSTRAINT_LAYOUT (manager));
+  constraints = (GListModel *)gtk_filter_list_model_new (all_constraints, omit_internal, NULL, NULL);
+  children = (GListModel *)gtk_filter_list_model_new (all_children, omit_internal, NULL, NULL);
+
+  list = g_list_store_new (G_TYPE_LIST_MODEL);
+  g_list_store_append (list, children);
+  g_list_store_append (list, guides);
+  g_list_store_append (list, constraints);
+  self->model = G_LIST_MODEL (gtk_flatten_list_model_new (G_TYPE_OBJECT, G_LIST_MODEL (list)));
+  g_object_unref (children);
+  g_object_unref (guides);
+  g_object_unref (constraints);
+  g_object_unref (all_children);
+  g_object_unref (all_constraints);
+  g_object_unref (list);
+
+
+  controller = (GtkEventController *)gtk_gesture_drag_new ();
+  g_signal_connect (controller, "drag-begin", G_CALLBACK (drag_begin), self);
+  g_signal_connect (controller, "drag-update", G_CALLBACK (drag_update), self);
+  g_signal_connect (controller, "drag-end", G_CALLBACK (drag_end), self);
+  gtk_widget_add_controller (GTK_WIDGET (self), controller);
+}
+
+ConstraintView *
+constraint_view_new (void)
+{
+  return g_object_new (CONSTRAINT_VIEW_TYPE, NULL);
+}
+
+void
+constraint_view_add_child (ConstraintView *view,
+                           const char     *name)
+{
+  GtkWidget *frame;
+  GtkWidget *label;
+
+  label = gtk_label_new (name);
+  frame = gtk_frame_new (NULL);
+  gtk_style_context_add_class (gtk_widget_get_style_context (frame), "child");
+  gtk_widget_set_name (frame, name);
+  gtk_container_add (GTK_CONTAINER (frame), label);
+  gtk_widget_set_parent (frame, GTK_WIDGET (view));
+
+  update_weak_position (view, frame, 100, 100);
+}
+
+void
+constraint_view_remove_child (ConstraintView *view,
+                              GtkWidget      *child)
+{
+  update_weak_position (view, child, -100, -100);
+  gtk_widget_unparent (child);
+}
+
+void
+constraint_view_add_guide (ConstraintView *view,
+                           GtkConstraintGuide *guide)
+{
+  GtkConstraintLayout *layout;
+  GtkWidget *frame;
+  GtkWidget *label;
+  const char *name;
+  GtkConstraint *constraint;
+  struct {
+    const char *name;
+    GtkConstraintAttribute attr;
+  } names[] = {
+    { "left-constraint", GTK_CONSTRAINT_ATTRIBUTE_LEFT },
+    { "top-constraint", GTK_CONSTRAINT_ATTRIBUTE_TOP },
+    { "width-constraint", GTK_CONSTRAINT_ATTRIBUTE_WIDTH },
+    { "height-constraint", GTK_CONSTRAINT_ATTRIBUTE_HEIGHT },
+  };
+  int i;
+
+  name = gtk_constraint_guide_get_name (guide);
+  label = gtk_label_new (name);
+  g_object_bind_property (guide, "name",
+                          label, "label",
+                          G_BINDING_DEFAULT);
+
+  frame = gtk_frame_new (NULL);
+  gtk_style_context_add_class (gtk_widget_get_style_context (frame), "guide");
+  g_object_set_data (G_OBJECT (frame), "internal", "yes");
+  gtk_container_add (GTK_CONTAINER (frame), label);
+  gtk_widget_insert_after (frame, GTK_WIDGET (view), NULL);
+
+  g_object_set_data (G_OBJECT (guide), "frame", frame);
+
+  layout = GTK_CONSTRAINT_LAYOUT (gtk_widget_get_layout_manager (GTK_WIDGET (view)));
+  gtk_constraint_layout_add_guide (layout, g_object_ref (guide));
+
+  for (i = 0; i < G_N_ELEMENTS (names); i++)
+    {
+      constraint = gtk_constraint_new (frame,
+                                       names[i].attr,
+                                       GTK_CONSTRAINT_RELATION_EQ,
+                                       guide,
+                                       names[i].attr,
+                                       1.0, 0.0,
+                                       GTK_CONSTRAINT_STRENGTH_REQUIRED);
+      g_object_set_data (G_OBJECT (constraint), "internal", "yes");
+      gtk_constraint_layout_add_constraint (layout, constraint);
+      g_object_set_data (G_OBJECT (guide), names[i].name, constraint);
+    }
+
+  update_weak_position (view, frame, 150, 150);
+}
+
+void
+constraint_view_remove_guide (ConstraintView     *view,
+                              GtkConstraintGuide *guide)
+{
+  GtkConstraintLayout *layout;
+  GtkWidget *frame;
+  GtkConstraint *constraint;
+  const char *names[] = {
+    "left-constraint",
+    "top-constraint",
+    "width-constraint",
+    "height-constraint"
+  };
+  int i;
+
+  layout = GTK_CONSTRAINT_LAYOUT (gtk_widget_get_layout_manager (GTK_WIDGET (view)));
+
+  for (i = 0; i < G_N_ELEMENTS (names); i++)
+    {
+      constraint = (GtkConstraint*)g_object_get_data (G_OBJECT (guide), names[i]);
+      gtk_constraint_layout_remove_constraint (layout, constraint);
+    }
+
+  frame = (GtkWidget *)g_object_get_data (G_OBJECT (guide), "frame");
+  update_weak_position (view, frame, -100, -100);
+  gtk_widget_unparent (frame);
+
+  gtk_constraint_layout_remove_guide (layout, guide);
+}
+
+void
+constraint_view_add_constraint (ConstraintView *view,
+                                GtkConstraint  *constraint)
+{
+  GtkLayoutManager *manager;
+
+  manager = gtk_widget_get_layout_manager (GTK_WIDGET (view));
+  gtk_constraint_layout_add_constraint (GTK_CONSTRAINT_LAYOUT (manager),
+                                        g_object_ref (constraint));
+}
+
+void
+constraint_view_remove_constraint (ConstraintView *view,
+                                   GtkConstraint  *constraint)
+{
+  GtkLayoutManager *manager;
+
+  manager = gtk_widget_get_layout_manager (GTK_WIDGET (view));
+  gtk_constraint_layout_remove_constraint (GTK_CONSTRAINT_LAYOUT (manager),
+                                           constraint);
+}
+
+GListModel *
+constraint_view_get_model (ConstraintView *view)
+{
+  return view->model;
+}

demos/constraint-editor/constraint-view.h

@@ -0,0 +1,44 @@
+/*
+ * Copyright © 2019 Red Hat, Inc
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Authors: Matthias Clasen
+ */
+
+#pragma once
+
+#include <gtk/gtk.h>
+
+#define CONSTRAINT_VIEW_TYPE (constraint_view_get_type ())
+
+G_DECLARE_FINAL_TYPE (ConstraintView, constraint_view, CONSTRAINT, VIEW, GtkWidget)
+
+ConstraintView * constraint_view_new (void);
+
+void             constraint_view_add_child (ConstraintView *view,
+                                            const char     *name);
+void             constraint_view_remove_child (ConstraintView *view,
+                                               GtkWidget      *child);
+void             constraint_view_add_guide (ConstraintView     *view,
+                                            GtkConstraintGuide *guide);
+void             constraint_view_remove_guide (ConstraintView     *view,
+                                               GtkConstraintGuide *guide);
+void             constraint_view_guide_changed (ConstraintView     *view,
+                                                GtkConstraintGuide *guide);
+void             constraint_view_add_constraint (ConstraintView *view,
+                                                 GtkConstraint  *constraint);
+void             constraint_view_remove_constraint (ConstraintView *view,
+                                                    GtkConstraint  *constraint);
+GListModel *     constraint_view_get_model (ConstraintView *view);

demos/constraint-editor/guide-editor.c

@@ -0,0 +1,411 @@
+/*
+ * Copyright © 2019 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Authors: Matthias Clasen
+ */
+
+#include "config.h"
+
+#include "guide-editor.h"
+
+struct _GuideEditor
+{
+  GtkWidget parent_instance;
+
+  GtkWidget *grid;
+  GtkWidget *name;
+  GtkWidget *min_width;
+  GtkWidget *min_height;
+  GtkWidget *nat_width;
+  GtkWidget *nat_height;
+  GtkWidget *max_width;
+  GtkWidget *max_height;
+  GtkWidget *strength;
+  GtkWidget *button;
+
+  GtkConstraintGuide *guide;
+
+  gboolean constructed;
+};
+
+enum {
+  PROP_GUIDE = 1,
+  LAST_PROP
+};
+
+static GParamSpec *pspecs[LAST_PROP];
+
+enum {
+  DONE,
+  LAST_SIGNAL
+};
+
+static guint signals[LAST_SIGNAL];
+
+G_DEFINE_TYPE(GuideEditor, guide_editor, GTK_TYPE_WIDGET);
+
+static void
+guide_strength_combo (GtkWidget *combo)
+{
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "weak", "Weak");
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "medium", "Medium");
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "strong", "Strong");
+  gtk_combo_box_text_append (GTK_COMBO_BOX_TEXT (combo), "required", "Required");
+}
+
+static GtkConstraintStrength
+get_strength (const char *id)
+{
+  GtkConstraintStrength strength;
+  GEnumClass *class = g_type_class_ref (GTK_TYPE_CONSTRAINT_STRENGTH);
+  GEnumValue *value = g_enum_get_value_by_nick (class, id);
+  strength = value->value;
+  g_type_class_unref (class);
+
+  return strength;
+}
+
+const char *
+get_strength_nick (GtkConstraintStrength strength)
+{
+  GEnumClass *class = g_type_class_ref (GTK_TYPE_CONSTRAINT_STRENGTH);
+  GEnumValue *value = g_enum_get_value (class, strength);
+  const char *nick = value->value_nick;
+  g_type_class_unref (class);
+
+  return nick;
+}
+
+void
+guide_editor_serialize_guide (GString *str,
+                              int      indent,
+                              GtkConstraintGuide *guide)
+{
+  int min_width, min_height;
+  int nat_width, nat_height;
+  int max_width, max_height;
+  const char *name;
+  const char *strength;
+
+  gtk_constraint_guide_get_min_size (guide, &min_width, &min_height);
+  gtk_constraint_guide_get_nat_size (guide, &nat_width, &nat_height);
+  gtk_constraint_guide_get_max_size (guide, &max_width, &max_height);
+  name = gtk_constraint_guide_get_name (guide);
+  strength = get_strength_nick (gtk_constraint_guide_get_strength (guide));
+
+  g_string_append_printf (str, "%*s<guide min-width=\"%d\" min-height=\"%d\"\n", indent, "", min_width, min_height);
+  g_string_append_printf (str, "%*s       nat-width=\"%d\" nat-height=\"%d\"\n", indent, "", nat_width, nat_height);
+  g_string_append_printf (str, "%*s       max-width=\"%d\" max-height=\"%d\"\n", indent, "", max_width, max_height);
+  g_string_append_printf (str, "%*s       name=\"%s\" strength=\"%s\" />\n", indent, "", name, strength);
+}
+
+static void
+create_guide (GtkButton   *button,
+              GuideEditor *editor)
+{
+  const char *id;
+  int strength;
+  const char *name;
+  int w, h;
+  GtkConstraintGuide *guide;
+
+  if (editor->guide)
+    guide = g_object_ref (editor->guide);
+  else
+    guide = gtk_constraint_guide_new ();
+
+  name = gtk_editable_get_text (GTK_EDITABLE (editor->name));
+  gtk_constraint_guide_set_name (guide, name);
+
+  w = gtk_spin_button_get_value_as_int (GTK_SPIN_BUTTON (editor->min_width));
+  h = gtk_spin_button_get_value_as_int (GTK_SPIN_BUTTON (editor->min_height));
+  gtk_constraint_guide_set_min_size (guide, w, h);
+
+  w = gtk_spin_button_get_value_as_int (GTK_SPIN_BUTTON (editor->nat_width));
+  h = gtk_spin_button_get_value_as_int (GTK_SPIN_BUTTON (editor->nat_height));
+  gtk_constraint_guide_set_nat_size (guide, w, h);
+
+  w = gtk_spin_button_get_value_as_int (GTK_SPIN_BUTTON (editor->max_width));
+  h = gtk_spin_button_get_value_as_int (GTK_SPIN_BUTTON (editor->max_height));
+  gtk_constraint_guide_set_max_size (guide, w, h);
+
+  id = gtk_combo_box_get_active_id (GTK_COMBO_BOX (editor->strength));
+  strength = get_strength (id);
+  gtk_constraint_guide_set_strength (guide, strength);
+
+  g_signal_emit (editor, signals[DONE], 0, guide);
+  g_object_unref (guide);
+}
+
+static void
+guide_editor_init (GuideEditor *editor)
+{
+  gtk_widget_init_template (GTK_WIDGET (editor));
+}
+
+static int guide_counter;
+
+static int
+min_input (GtkSpinButton *spin_button,
+           double        *new_val)
+{
+  if (strcmp (gtk_editable_get_text (GTK_EDITABLE (spin_button)), "") == 0)
+    {
+      *new_val = 0.0;
+      return TRUE;
+    }
+
+  return FALSE;
+}
+
+static int
+max_input (GtkSpinButton *spin_button,
+           double        *new_val)
+{
+  if (strcmp (gtk_editable_get_text (GTK_EDITABLE (spin_button)), "") == 0)
+    {
+      *new_val = G_MAXINT;
+      return TRUE;
+    }
+
+  return FALSE;
+}
+
+static gboolean
+min_output (GtkSpinButton *spin_button)
+{
+  GtkAdjustment *adjustment;
+  double value;
+  GtkWidget *box, *text;
+
+  adjustment = gtk_spin_button_get_adjustment (spin_button);
+  value = gtk_adjustment_get_value (adjustment);
+
+  box = gtk_widget_get_first_child (GTK_WIDGET (spin_button));
+  text = gtk_widget_get_first_child (box);
+
+  if (value == 0.0)
+    {
+      gtk_editable_set_text (GTK_EDITABLE (spin_button), "");
+      gtk_text_set_placeholder_text (GTK_TEXT (text), "unset");
+      return TRUE;
+    }
+  else
+    {
+      gtk_text_set_placeholder_text (GTK_TEXT (text), "");
+      return FALSE;
+    }
+}
+
+static gboolean
+max_output (GtkSpinButton *spin_button)
+{
+  GtkAdjustment *adjustment;
+  double value;
+  GtkWidget *box, *text;
+
+  adjustment = gtk_spin_button_get_adjustment (spin_button);
+  value = gtk_adjustment_get_value (adjustment);
+
+  box = gtk_widget_get_first_child (GTK_WIDGET (spin_button));
+  text = gtk_widget_get_first_child (box);
+
+  if (value == (double)G_MAXINT)
+    {
+      gtk_editable_set_text (GTK_EDITABLE (spin_button), "");
+      gtk_text_set_placeholder_text (GTK_TEXT (text), "unset");
+      return TRUE;
+    }
+  else
+    {
+      gtk_text_set_placeholder_text (GTK_TEXT (text), "");
+      return FALSE;
+    }
+}
+
+static void
+guide_editor_constructed (GObject *object)
+{
+  GuideEditor *editor = GUIDE_EDITOR (object);
+
+  guide_strength_combo (editor->strength);
+
+  g_signal_connect (editor->min_width, "input", G_CALLBACK (min_input), NULL);
+  g_signal_connect (editor->min_width, "output", G_CALLBACK (min_output), NULL);
+
+  g_signal_connect (editor->min_height, "input", G_CALLBACK (min_input), NULL);
+  g_signal_connect (editor->min_height, "output", G_CALLBACK (min_output), NULL);
+
+  g_signal_connect (editor->max_width, "input", G_CALLBACK (max_input), NULL);
+  g_signal_connect (editor->max_width, "output", G_CALLBACK (max_output), NULL);
+
+  g_signal_connect (editor->max_height, "input", G_CALLBACK (max_input), NULL);
+  g_signal_connect (editor->max_height, "output", G_CALLBACK (max_output), NULL);
+
+  if (editor->guide)
+    {
+      GtkConstraintStrength strength;
+      const char *nick;
+      int w, h;
+
+      nick = gtk_constraint_guide_get_name (editor->guide);
+      if (nick)
+        gtk_editable_set_text (GTK_EDITABLE (editor->name), nick);
+
+      gtk_constraint_guide_get_min_size (editor->guide, &w, &h);
+      gtk_spin_button_set_value (GTK_SPIN_BUTTON (editor->min_width), w);
+      gtk_spin_button_set_value (GTK_SPIN_BUTTON (editor->min_height), h);
+
+      gtk_constraint_guide_get_nat_size (editor->guide, &w, &h);
+      gtk_spin_button_set_value (GTK_SPIN_BUTTON (editor->nat_width), w);
+      gtk_spin_button_set_value (GTK_SPIN_BUTTON (editor->nat_height), h);
+
+      gtk_constraint_guide_get_max_size (editor->guide, &w, &h);
+      gtk_spin_button_set_value (GTK_SPIN_BUTTON (editor->max_width), w);
+      gtk_spin_button_set_value (GTK_SPIN_BUTTON (editor->max_height), h);
+
+      strength = gtk_constraint_guide_get_strength (editor->guide);
+      nick = get_strength_nick (strength);
+      gtk_combo_box_set_active_id (GTK_COMBO_BOX (editor->strength), nick);
+
+      gtk_button_set_label (GTK_BUTTON (editor->button), "Apply");
+    }
+  else
+    {
+      char *name;
+
+      guide_counter++;
+      name = g_strdup_printf ("Guide %d", guide_counter);
+      gtk_editable_set_text (GTK_EDITABLE (editor->name), name);
+      g_free (name);
+
+      gtk_spin_button_set_value (GTK_SPIN_BUTTON (editor->min_width), 0.0);
+      gtk_spin_button_set_value (GTK_SPIN_BUTTON (editor->min_height), 0.0);
+      gtk_spin_button_set_value (GTK_SPIN_BUTTON (editor->nat_width), 0.0);
+      gtk_spin_button_set_value (GTK_SPIN_BUTTON (editor->nat_height), 0.0);
+      gtk_spin_button_set_value (GTK_SPIN_BUTTON (editor->max_width), G_MAXINT);
+      gtk_spin_button_set_value (GTK_SPIN_BUTTON (editor->max_height), G_MAXINT);
+
+      gtk_combo_box_set_active_id (GTK_COMBO_BOX (editor->strength), "medium");
+
+      gtk_button_set_label (GTK_BUTTON (editor->button), "Create");
+    }
+
+  editor->constructed = TRUE;
+}
+
+static void
+guide_editor_set_property (GObject      *object,
+                           guint         property_id,
+                           const GValue *value,
+                           GParamSpec   *pspec)
+{
+  GuideEditor *self = GUIDE_EDITOR (object);
+
+  switch (property_id)
+    {
+    case PROP_GUIDE:
+      self->guide = g_value_dup_object (value);
+      break;
+
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
+    }
+}
+
+static void
+guide_editor_get_property (GObject    *object,
+                           guint       property_id,
+                           GValue     *value,
+                           GParamSpec *pspec)
+{
+  GuideEditor *self = GUIDE_EDITOR (object);
+
+  switch (property_id)
+    {
+    case PROP_GUIDE:
+      g_value_set_object (value, self->guide);
+      break;
+
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
+    }
+}
+
+static void
+guide_editor_dispose (GObject *object)
+{
+  GuideEditor *self = (GuideEditor *)object;
+
+  g_clear_pointer (&self->grid, gtk_widget_unparent);
+  g_clear_object (&self->guide);
+
+  G_OBJECT_CLASS (guide_editor_parent_class)->dispose (object);
+}
+
+static void
+guide_editor_class_init (GuideEditorClass *class)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (class);
+  GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (class);
+
+  object_class->constructed = guide_editor_constructed;
+  object_class->dispose = guide_editor_dispose;
+  object_class->set_property = guide_editor_set_property;
+  object_class->get_property = guide_editor_get_property;
+
+  pspecs[PROP_GUIDE] =
+    g_param_spec_object ("guide", "guide", "guide",
+                         GTK_TYPE_CONSTRAINT_GUIDE,
+                         G_PARAM_READWRITE|G_PARAM_CONSTRUCT_ONLY);
+
+  g_object_class_install_properties (object_class, LAST_PROP, pspecs);
+
+  signals[DONE] =
+    g_signal_new ("done",
+                  G_TYPE_FROM_CLASS (object_class),
+                  G_SIGNAL_RUN_LAST,
+                  0,
+                  NULL, NULL,
+                  NULL,
+                  G_TYPE_NONE, 1, GTK_TYPE_CONSTRAINT_GUIDE);
+
+  gtk_widget_class_set_layout_manager_type (widget_class, GTK_TYPE_BIN_LAYOUT);
+
+  gtk_widget_class_set_template_from_resource (widget_class,
+                                               "/org/gtk/gtk4/constraint-editor/guide-editor.ui");
+
+  gtk_widget_class_bind_template_child (widget_class, GuideEditor, grid);
+  gtk_widget_class_bind_template_child (widget_class, GuideEditor, name);
+  gtk_widget_class_bind_template_child (widget_class, GuideEditor, min_width);
+  gtk_widget_class_bind_template_child (widget_class, GuideEditor, min_height);
+  gtk_widget_class_bind_template_child (widget_class, GuideEditor, nat_width);
+  gtk_widget_class_bind_template_child (widget_class, GuideEditor, nat_height);
+  gtk_widget_class_bind_template_child (widget_class, GuideEditor, max_width);
+  gtk_widget_class_bind_template_child (widget_class, GuideEditor, max_height);
+  gtk_widget_class_bind_template_child (widget_class, GuideEditor, strength);
+  gtk_widget_class_bind_template_child (widget_class, GuideEditor, button);
+
+  gtk_widget_class_bind_template_callback (widget_class, create_guide);
+}
+
+GuideEditor *
+guide_editor_new (GtkConstraintGuide *guide)
+{
+  return g_object_new (GUIDE_EDITOR_TYPE,
+                       "guide", guide,
+                       NULL);
+}

demos/constraint-editor/guide-editor.h

@@ -0,0 +1,32 @@
+/*
+ * Copyright © 2019 Red Hat, Inc
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Authors: Matthias Clasen
+ */
+
+#pragma once
+
+#include <gtk/gtk.h>
+
+#define GUIDE_EDITOR_TYPE (guide_editor_get_type ())
+
+G_DECLARE_FINAL_TYPE (GuideEditor, guide_editor, GUIDE, EDITOR, GtkWidget)
+
+GuideEditor * guide_editor_new (GtkConstraintGuide  *guide);
+
+void guide_editor_serialize_guide (GString            *str,
+                                   int                 indent,
+                                   GtkConstraintGuide *guide);

demos/constraint-editor/guide-editor.ui

@@ -0,0 +1,188 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<interface>
+  <object class="GtkAdjustment" id="min_width_adj">
+    <property name="lower">0</property>
+    <property name="upper">2147483647</property>
+    <property name="step-increment">1</property>
+    <property name="page-increment">10</property>
+    <property name="page-size">0</property>
+  </object>
+  <object class="GtkAdjustment" id="min_height_adj">
+    <property name="lower">0</property>
+    <property name="upper">2147483647</property>
+    <property name="step-increment">1</property>
+    <property name="page-increment">10</property>
+    <property name="page-size">0</property>
+  </object>
+  <object class="GtkAdjustment" id="nat_width_adj">
+    <property name="lower">0</property>
+    <property name="upper">2147483647</property>
+    <property name="step-increment">1</property>
+    <property name="page-increment">10</property>
+    <property name="page-size">0</property>
+  </object>
+  <object class="GtkAdjustment" id="nat_height_adj">
+    <property name="lower">0</property>
+    <property name="upper">2147483647</property>
+    <property name="step-increment">1</property>
+    <property name="page-increment">10</property>
+    <property name="page-size">0</property>
+  </object>
+  <object class="GtkAdjustment" id="max_width_adj">
+    <property name="lower">0</property>
+    <property name="upper">2147483647</property>
+    <property name="step-increment">1</property>
+    <property name="page-increment">10</property>
+    <property name="page-size">0</property>
+  </object>
+  <object class="GtkAdjustment" id="max_height_adj">
+    <property name="lower">0</property>
+    <property name="upper">2147483647</property>
+    <property name="step-increment">1</property>
+    <property name="page-increment">10</property>
+    <property name="page-size">0</property>
+  </object>
+  <template class="GuideEditor" parent="GtkWidget">
+    <child>
+      <object class="GtkGrid" id="grid">
+        <property name="margin">20</property>
+        <property name="row-spacing">10</property>
+        <property name="column-spacing">10</property>
+        <child>
+          <object class="GtkLabel">
+            <property name="label">Name</property>
+            <layout>
+              <property name="left-attach">0</property>
+              <property name="top-attach">0</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkEntry" id="name">
+            <property name="max-width-chars">20</property>
+            <layout>
+              <property name="left-attach">1</property>
+              <property name="top-attach">0</property>
+              <property name="column-span">2</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkLabel">
+            <property name="label">Min Size</property>
+            <layout>
+              <property name="left-attach">0</property>
+              <property name="top-attach">1</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkSpinButton" id="min_width">
+            <property name="adjustment">min_width_adj</property>
+            <property name="max-width-chars">5</property>
+            <layout>
+              <property name="left-attach">1</property>
+              <property name="top-attach">1</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkSpinButton" id="min_height">
+            <property name="adjustment">min_height_adj</property>
+            <property name="max-width-chars">5</property>
+            <layout>
+              <property name="left-attach">2</property>
+              <property name="top-attach">1</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkLabel">
+            <property name="label">Nat Size</property>
+            <layout>
+              <property name="left-attach">0</property>
+              <property name="top-attach">2</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkSpinButton" id="nat_width">
+            <property name="adjustment">nat_width_adj</property>
+            <property name="max-width-chars">5</property>
+            <layout>
+              <property name="left-attach">1</property>
+              <property name="top-attach">2</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkSpinButton" id="nat_height">
+            <property name="adjustment">nat_height_adj</property>
+            <property name="max-width-chars">5</property>
+            <layout>
+              <property name="left-attach">2</property>
+              <property name="top-attach">2</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkLabel">
+            <property name="label">Max Size</property>
+            <layout>
+              <property name="left-attach">0</property>
+              <property name="top-attach">3</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkSpinButton" id="max_width">
+            <property name="adjustment">max_width_adj</property>
+            <property name="max-width-chars">5</property>
+            <layout>
+              <property name="left-attach">1</property>
+              <property name="top-attach">3</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkSpinButton" id="max_height">
+            <property name="adjustment">max_height_adj</property>
+            <property name="max-width-chars">5</property>
+            <layout>
+              <property name="left-attach">2</property>
+              <property name="top-attach">3</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkLabel">
+            <property name="label">Strength</property>
+            <layout>
+              <property name="left-attach">0</property>
+              <property name="top-attach">4</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkComboBoxText" id="strength">
+            <layout>
+              <property name="left-attach">1</property>
+              <property name="top-attach">4</property>
+              <property name="column-span">2</property>
+            </layout>
+          </object>
+        </child>
+        <child>
+          <object class="GtkButton" id="button">
+            <property name="label">Create</property>
+            <signal name="clicked" handler="create_guide"/>
+            <layout>
+              <property name="left-attach">2</property>
+              <property name="top-attach">5</property>
+            </layout>
+          </object>
+        </child>
+      </object>
+    </child>
+  </template>
+</interface>

demos/constraint-editor/main.c

@@ -0,0 +1,28 @@
+/*
+ * Copyright © 2019 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Authors: Matthias Clasen <mclasen@redhat.com>
+ */
+
+#include "config.h"
+
+#include <constraint-editor-application.h>
+
+int
+main (int argc, char *argv[])
+{
+  return g_application_run (G_APPLICATION (constraint_editor_application_new ()), argc, argv);
+}

demos/constraint-editor/meson.build

@@ -0,0 +1,20 @@
+constraint_editor_sources = [
+  'main.c',
+  'constraint-editor-application.c',
+  'constraint-editor-window.c',
+  'constraint-view.c',
+  'constraint-editor.c',
+  'guide-editor.c',
+]
+
+constraint_editor_resources = gnome.compile_resources('constraint_editor_resources',
+                                                      'constraint-editor.gresource.xml',
+                                                      source_dir: '.')
+
+executable('gtk4-constraint-editor',
+           constraint_editor_sources, constraint_editor_resources,
+           dependencies: libgtk_dep,
+           include_directories: confinc,
+           gui_app: true,
+           link_args: extra_demo_ldflags,
+           install: false)

demos/gtk-demo/constraints.c

@@ -0,0 +1,289 @@
+/* Constraints/Simple
+ *
+ * GtkConstraintLayout provides a layout manager that uses relations
+ * between widgets (also known as "constraints") to compute the position
+ * and size of each child.
+ */
+
+#include <glib/gi18n.h>
+#include <gtk/gtk.h>
+
+G_DECLARE_FINAL_TYPE (SimpleGrid, simple_grid, SIMPLE, GRID, GtkWidget)
+
+struct _SimpleGrid
+{
+  GtkWidget parent_instance;
+
+  GtkWidget *button1, *button2;
+  GtkWidget *button3;
+};
+
+G_DEFINE_TYPE (SimpleGrid, simple_grid, GTK_TYPE_WIDGET)
+
+static void
+simple_grid_destroy (GtkWidget *widget)
+{
+  SimpleGrid *self = SIMPLE_GRID (widget);
+
+  g_clear_pointer (&self->button1, gtk_widget_destroy);
+  g_clear_pointer (&self->button2, gtk_widget_destroy);
+  g_clear_pointer (&self->button3, gtk_widget_destroy);
+
+  GTK_WIDGET_CLASS (simple_grid_parent_class)->destroy (widget);
+}
+
+static void
+simple_grid_class_init (SimpleGridClass *klass)
+{
+  GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (klass);
+
+  widget_class->destroy = simple_grid_destroy;
+
+  gtk_widget_class_set_layout_manager_type (widget_class, GTK_TYPE_CONSTRAINT_LAYOUT);
+}
+
+/* Layout:
+ *
+ *   +-------------------------------------+
+ *   | +-----------++-------++-----------+ |
+ *   | |  Child 1  || Space ||  Child 2  | |
+ *   | +-----------++-------++-----------+ |
+ *   | +---------------------------------+ |
+ *   | |             Child 3             | |
+ *   | +---------------------------------+ |
+ *   +-------------------------------------+
+ *
+ * Constraints:
+ *
+ *   super.start = child1.start - 8
+ *   child1.width = child2.width
+ *   child1.end = space.start
+ *   space.end = child2.start
+ *   child2.end = super.end - 8
+ *   super.start = child3.start - 8
+ *   child3.end = super.end - 8
+ *   super.top = child1.top - 8
+ *   super.top = child2.top - 8
+ *   child1.bottom = child3.top - 12
+ *   child2.bottom = child3.top - 12
+ *   child3.height = child1.height
+ *   child3.height = child2.height
+ *   child3.bottom = super.bottom - 8
+ *
+ * To add some flexibility, we make the space
+ * stretchable:
+ *
+ *   space.width >= 10
+ *   space.width = 100
+ *   space.width <= 200
+ */
+static void
+build_constraints (SimpleGrid          *self,
+                   GtkConstraintLayout *manager)
+{
+  GtkConstraintGuide *guide;
+
+  guide = gtk_constraint_guide_new ();
+  gtk_constraint_guide_set_name (guide, "space");
+  gtk_constraint_guide_set_min_size (guide, 10, 10);
+  gtk_constraint_guide_set_nat_size (guide, 100, 10);
+  gtk_constraint_guide_set_max_size (guide, 200, 20);
+  gtk_constraint_guide_set_strength (guide, GTK_CONSTRAINT_STRENGTH_STRONG);
+  gtk_constraint_layout_add_guide (manager, guide);
+
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new_constant (GTK_CONSTRAINT_TARGET (self->button1),
+                        GTK_CONSTRAINT_ATTRIBUTE_WIDTH,
+                        GTK_CONSTRAINT_RELATION_LE,
+                        200.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (NULL,
+                        GTK_CONSTRAINT_ATTRIBUTE_START,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        self->button1,
+                        GTK_CONSTRAINT_ATTRIBUTE_START,
+                        1.0,
+                        -8.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (self->button1,
+                        GTK_CONSTRAINT_ATTRIBUTE_WIDTH,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        self->button2,
+                        GTK_CONSTRAINT_ATTRIBUTE_WIDTH,
+                        1.0,
+                        0.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (self->button1,
+                        GTK_CONSTRAINT_ATTRIBUTE_END,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        guide,
+                        GTK_CONSTRAINT_ATTRIBUTE_START,
+                        1.0,
+                        0.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (guide,
+                        GTK_CONSTRAINT_ATTRIBUTE_END,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        self->button2,
+                        GTK_CONSTRAINT_ATTRIBUTE_START,
+                        1.0,
+                        0.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (self->button2,
+                        GTK_CONSTRAINT_ATTRIBUTE_END,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        NULL,
+                        GTK_CONSTRAINT_ATTRIBUTE_END,
+                        1.0,
+                        -8.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (NULL,
+                        GTK_CONSTRAINT_ATTRIBUTE_START,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        self->button3,
+                        GTK_CONSTRAINT_ATTRIBUTE_START,
+                        1.0,
+                        -8.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (self->button3,
+                        GTK_CONSTRAINT_ATTRIBUTE_END,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        NULL,
+                        GTK_CONSTRAINT_ATTRIBUTE_END,
+                        1.0,
+                        -8.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (NULL,
+                        GTK_CONSTRAINT_ATTRIBUTE_TOP,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        self->button1,
+                        GTK_CONSTRAINT_ATTRIBUTE_TOP,
+                        1.0,
+                        -8.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (NULL,
+                        GTK_CONSTRAINT_ATTRIBUTE_TOP,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        self->button2,
+                        GTK_CONSTRAINT_ATTRIBUTE_TOP,
+                        1.0,
+                        -8.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (self->button1,
+                        GTK_CONSTRAINT_ATTRIBUTE_BOTTOM,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        self->button3,
+                        GTK_CONSTRAINT_ATTRIBUTE_TOP,
+                        1.0,
+                        -12.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (self->button2,
+                        GTK_CONSTRAINT_ATTRIBUTE_BOTTOM,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        self->button3,
+                        GTK_CONSTRAINT_ATTRIBUTE_TOP,
+                        1.0,
+                        -12.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (self->button3,
+                        GTK_CONSTRAINT_ATTRIBUTE_HEIGHT,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        self->button1,
+                        GTK_CONSTRAINT_ATTRIBUTE_HEIGHT,
+                        1.0,
+                        0.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (self->button3,
+                        GTK_CONSTRAINT_ATTRIBUTE_HEIGHT,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        self->button2,
+                        GTK_CONSTRAINT_ATTRIBUTE_HEIGHT,
+                        1.0,
+                        0.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (self->button3,
+                        GTK_CONSTRAINT_ATTRIBUTE_BOTTOM,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        NULL,
+                        GTK_CONSTRAINT_ATTRIBUTE_BOTTOM,
+                        1.0,
+                        -8.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+}
+
+static void
+simple_grid_init (SimpleGrid *self)
+{
+  GtkWidget *widget = GTK_WIDGET (self);
+
+  self->button1 = gtk_button_new_with_label ("Child 1");
+  gtk_widget_set_parent (self->button1, widget);
+  gtk_widget_set_name (self->button1, "button1");
+
+  self->button2 = gtk_button_new_with_label ("Child 2");
+  gtk_widget_set_parent (self->button2, widget);
+  gtk_widget_set_name (self->button2, "button2");
+
+  self->button3 = gtk_button_new_with_label ("Child 3");
+  gtk_widget_set_parent (self->button3, widget);
+  gtk_widget_set_name (self->button3, "button3");
+
+  GtkLayoutManager *manager = gtk_widget_get_layout_manager (GTK_WIDGET (self));
+  build_constraints (self, GTK_CONSTRAINT_LAYOUT (manager));
+}
+
+GtkWidget *
+do_constraints (GtkWidget *do_widget)
+{
+ static GtkWidget *window;
+
+ if (!window)
+   {
+     GtkWidget *header, *box, *grid, *button;
+
+     window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
+     gtk_window_set_display (GTK_WINDOW (window), gtk_widget_get_display (do_widget));
+
+     header = gtk_header_bar_new ();
+     gtk_header_bar_set_title (GTK_HEADER_BAR (header), "Constraints");
+     gtk_header_bar_set_show_title_buttons (GTK_HEADER_BAR (header), FALSE);
+     gtk_window_set_titlebar (GTK_WINDOW (window), header);
+     g_signal_connect (window, "destroy",
+                       G_CALLBACK (gtk_widget_destroyed), &window);
+
+     box = gtk_box_new (GTK_ORIENTATION_VERTICAL, 12);
+     gtk_container_add (GTK_CONTAINER (window), box);
+
+     grid = g_object_new (simple_grid_get_type (), NULL);
+     gtk_widget_set_hexpand (grid, TRUE);
+     gtk_widget_set_vexpand (grid, TRUE);
+     gtk_container_add (GTK_CONTAINER (box), grid);
+
+     button = gtk_button_new_with_label ("Close");
+     gtk_container_add (GTK_CONTAINER (box), button);
+     gtk_widget_set_hexpand (grid, TRUE);
+     g_signal_connect_swapped (button, "clicked",
+                               G_CALLBACK (gtk_widget_destroy), window);
+   }
+
+ if (!gtk_widget_get_visible (window))
+   gtk_widget_show (window);
+ else
+   gtk_widget_destroy (window);
+
+ return window;
+}

demos/gtk-demo/constraints2.c

@@ -0,0 +1,245 @@
+/* Constraints/Interactive
+ *
+ * Demonstrate how constraints can be updates during
+ * user interaction.
+ */
+
+#include <glib/gi18n.h>
+#include <gtk/gtk.h>
+
+G_DECLARE_FINAL_TYPE (InteractiveGrid, interactive_grid, INTERACTIVE, GRID, GtkWidget)
+
+struct _InteractiveGrid
+{
+  GtkWidget parent_instance;
+
+  GtkWidget *button1, *button2;
+  GtkWidget *button3;
+  GtkConstraintGuide *guide;
+  GtkConstraint *constraint;
+};
+
+G_DEFINE_TYPE (InteractiveGrid, interactive_grid, GTK_TYPE_WIDGET)
+
+static void
+interactive_grid_destroy (GtkWidget *widget)
+{
+  InteractiveGrid *self = INTERACTIVE_GRID (widget);
+
+  g_clear_pointer (&self->button1, gtk_widget_destroy);
+  g_clear_pointer (&self->button2, gtk_widget_destroy);
+  g_clear_pointer (&self->button3, gtk_widget_destroy);
+
+  GTK_WIDGET_CLASS (interactive_grid_parent_class)->destroy (widget);
+}
+
+static void
+interactive_grid_class_init (InteractiveGridClass *klass)
+{
+  GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (klass);
+
+  widget_class->destroy = interactive_grid_destroy;
+
+  gtk_widget_class_set_layout_manager_type (widget_class, GTK_TYPE_CONSTRAINT_LAYOUT);
+}
+
+static void
+build_constraints (InteractiveGrid          *self,
+                   GtkConstraintLayout *manager)
+{
+  self->guide = g_object_new (GTK_TYPE_CONSTRAINT_GUIDE, NULL);
+  gtk_constraint_layout_add_guide (manager, self->guide);
+
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new_constant (GTK_CONSTRAINT_TARGET (self->guide),
+                        GTK_CONSTRAINT_ATTRIBUTE_WIDTH,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        0.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (NULL,
+                        GTK_CONSTRAINT_ATTRIBUTE_START,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        GTK_CONSTRAINT_TARGET (self->button1),
+                        GTK_CONSTRAINT_ATTRIBUTE_START,
+                        1.0,
+                        -8.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (GTK_CONSTRAINT_TARGET (self->button1),
+                        GTK_CONSTRAINT_ATTRIBUTE_END,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        GTK_CONSTRAINT_TARGET (self->guide),
+                        GTK_CONSTRAINT_ATTRIBUTE_START,
+                        1.0,
+                        0.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (GTK_CONSTRAINT_TARGET (self->button2),
+                        GTK_CONSTRAINT_ATTRIBUTE_START,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        GTK_CONSTRAINT_TARGET (self->guide),
+                        GTK_CONSTRAINT_ATTRIBUTE_END,
+                        1.0,
+                        0.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (GTK_CONSTRAINT_TARGET (self->button2),
+                        GTK_CONSTRAINT_ATTRIBUTE_END,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        NULL,
+                        GTK_CONSTRAINT_ATTRIBUTE_END,
+                        1.0,
+                        -8.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (NULL,
+                        GTK_CONSTRAINT_ATTRIBUTE_START,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        GTK_CONSTRAINT_TARGET (self->button3),
+                        GTK_CONSTRAINT_ATTRIBUTE_START,
+                        1.0,
+                        -8.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (GTK_CONSTRAINT_TARGET (self->button3),
+                        GTK_CONSTRAINT_ATTRIBUTE_END,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        GTK_CONSTRAINT_TARGET (self->guide),
+                        GTK_CONSTRAINT_ATTRIBUTE_START,
+                        1.0,
+                        0.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (NULL,
+                        GTK_CONSTRAINT_ATTRIBUTE_TOP,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        GTK_CONSTRAINT_TARGET (self->button1),
+                        GTK_CONSTRAINT_ATTRIBUTE_TOP,
+                        1.0,
+                        -8.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (GTK_CONSTRAINT_TARGET (self->button2),
+                        GTK_CONSTRAINT_ATTRIBUTE_TOP,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        GTK_CONSTRAINT_TARGET (self->button1),
+                        GTK_CONSTRAINT_ATTRIBUTE_BOTTOM,
+                        1.0,
+                        0.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (GTK_CONSTRAINT_TARGET (self->button3),
+                        GTK_CONSTRAINT_ATTRIBUTE_TOP,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        GTK_CONSTRAINT_TARGET (self->button2),
+                        GTK_CONSTRAINT_ATTRIBUTE_BOTTOM,
+                        1.0,
+                        0.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+  gtk_constraint_layout_add_constraint (manager,
+    gtk_constraint_new (GTK_CONSTRAINT_TARGET (self->button3),
+                        GTK_CONSTRAINT_ATTRIBUTE_BOTTOM,
+                        GTK_CONSTRAINT_RELATION_EQ,
+                        NULL,
+                        GTK_CONSTRAINT_ATTRIBUTE_BOTTOM,
+                        1.0,
+                        -8.0,
+                        GTK_CONSTRAINT_STRENGTH_REQUIRED));
+}
+
+static void
+drag_cb (GtkGestureDrag  *drag,
+         double           offset_x,
+         double           offset_y,
+         InteractiveGrid *self)
+{
+  GtkConstraintLayout *layout = GTK_CONSTRAINT_LAYOUT (gtk_widget_get_layout_manager (GTK_WIDGET (self)));
+  double x, y;
+
+  if (self->constraint)
+    {
+      gtk_constraint_layout_remove_constraint (layout, self->constraint);
+      g_clear_object (&self->constraint);
+    }
+
+  gtk_gesture_drag_get_start_point (drag, &x, &y);
+  self->constraint = gtk_constraint_new_constant (GTK_CONSTRAINT_TARGET (self->guide),
+                                                  GTK_CONSTRAINT_ATTRIBUTE_LEFT,
+                                                  GTK_CONSTRAINT_RELATION_EQ,
+                                                  x + offset_x,
+                                                  GTK_CONSTRAINT_STRENGTH_REQUIRED);
+  gtk_constraint_layout_add_constraint (layout, g_object_ref (self->constraint));
+  gtk_widget_queue_allocate (GTK_WIDGET (self));
+}
+
+static void
+interactive_grid_init (InteractiveGrid *self)
+{
+  GtkWidget *widget = GTK_WIDGET (self);
+  GtkGesture *drag;
+
+  self->button1 = gtk_button_new_with_label ("Child 1");
+  gtk_widget_set_parent (self->button1, widget);
+  gtk_widget_set_name (self->button1, "button1");
+
+  self->button2 = gtk_button_new_with_label ("Child 2");
+  gtk_widget_set_parent (self->button2, widget);
+  gtk_widget_set_name (self->button2, "button2");
+
+  self->button3 = gtk_button_new_with_label ("Child 3");
+  gtk_widget_set_parent (self->button3, widget);
+  gtk_widget_set_name (self->button3, "button3");
+
+  GtkLayoutManager *manager = gtk_widget_get_layout_manager (GTK_WIDGET (self));
+  build_constraints (self, GTK_CONSTRAINT_LAYOUT (manager));
+
+  drag = gtk_gesture_drag_new ();
+  g_signal_connect (drag, "drag-update", G_CALLBACK (drag_cb), self);
+  gtk_widget_add_controller (GTK_WIDGET (self), GTK_EVENT_CONTROLLER (drag));
+}
+
+GtkWidget *
+do_constraints2 (GtkWidget *do_widget)
+{
+ static GtkWidget *window;
+
+ if (!window)
+   {
+     GtkWidget *header, *box, *grid, *button;
+
+     window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
+     gtk_window_set_display (GTK_WINDOW (window), gtk_widget_get_display (do_widget));
+
+     header = gtk_header_bar_new ();
+     gtk_header_bar_set_title (GTK_HEADER_BAR (header), "Constraints");
+     gtk_header_bar_set_show_title_buttons (GTK_HEADER_BAR (header), FALSE);
+     gtk_window_set_titlebar (GTK_WINDOW (window), header);
+     g_signal_connect (window, "destroy",
+                       G_CALLBACK (gtk_widget_destroyed), &window);
+
+     box = gtk_box_new (GTK_ORIENTATION_VERTICAL, 12);
+     gtk_container_add (GTK_CONTAINER (window), box);
+
+     grid = g_object_new (interactive_grid_get_type (), NULL);
+     gtk_widget_set_hexpand (grid, TRUE);
+     gtk_widget_set_vexpand (grid, TRUE);
+     gtk_container_add (GTK_CONTAINER (box), grid);
+
+     button = gtk_button_new_with_label ("Close");
+     gtk_container_add (GTK_CONTAINER (box), button);
+     gtk_widget_set_hexpand (grid, TRUE);
+     g_signal_connect_swapped (button, "clicked",
+                               G_CALLBACK (gtk_widget_destroy), window);
+   }
+
+ if (!gtk_widget_get_visible (window))
+   gtk_widget_show (window);
+ else
+   gtk_widget_destroy (window);
+
+ return window;
+}

demos/gtk-demo/constraints3.c

@@ -0,0 +1,165 @@
+/* Constraints/VFL
+ *
+ * GtkConstraintLayout allows defining constraints using a
+ * compact syntax called Visual Format Language, or VFL.
+ */
+
+#include <glib/gi18n.h>
+#include <gtk/gtk.h>
+
+G_DECLARE_FINAL_TYPE (VflGrid, vfl_grid, VFL, GRID, GtkWidget)
+
+struct _VflGrid
+{
+  GtkWidget parent_instance;
+
+  GtkWidget *button1, *button2;
+  GtkWidget *button3;
+};
+
+G_DEFINE_TYPE (VflGrid, vfl_grid, GTK_TYPE_WIDGET)
+
+static void
+vfl_grid_destroy (GtkWidget *widget)
+{
+  VflGrid *self = VFL_GRID (widget);
+
+  g_clear_pointer (&self->button1, gtk_widget_destroy);
+  g_clear_pointer (&self->button2, gtk_widget_destroy);
+  g_clear_pointer (&self->button3, gtk_widget_destroy);
+
+  GTK_WIDGET_CLASS (vfl_grid_parent_class)->destroy (widget);
+}
+
+static void
+vfl_grid_class_init (VflGridClass *klass)
+{
+  GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (klass);
+
+  widget_class->destroy = vfl_grid_destroy;
+
+  gtk_widget_class_set_layout_manager_type (widget_class, GTK_TYPE_CONSTRAINT_LAYOUT);
+}
+
+/* Layout:
+ *
+ *   +-----------------------------+
+ *   | +-----------+ +-----------+ |
+ *   | |  Child 1  | |  Child 2  | |
+ *   | +-----------+ +-----------+ |
+ *   | +-------------------------+ |
+ *   | |         Child 3         | |
+ *   | +-------------------------+ |
+ *   +-----------------------------+
+ *
+ * Constraints:
+ *
+ *   super.start = child1.start - 8
+ *   child1.width = child2.width
+ *   child1.end = child2.start - 12
+ *   child2.end = super.end - 8
+ *   super.start = child3.start - 8
+ *   child3.end = super.end - 8
+ *   super.top = child1.top - 8
+ *   super.top = child2.top - 8
+ *   child1.bottom = child3.top - 12
+ *   child2.bottom = child3.top - 12
+ *   child3.height = child1.height
+ *   child3.height = child2.height
+ *   child3.bottom = super.bottom - 8
+ *
+ * Visual format:
+ *
+ *   H:|-8-[view1(==view2)-12-[view2]-8-|
+ *   H:|-8-[view3]-8-|
+ *   V:|-8-[view1]-12-[view3(==view1)]-8-|
+ *   V:|-8-[view2]-12-[view3(==view2)]-8-|
+ */
+static void
+build_constraints (VflGrid          *self,
+                   GtkConstraintLayout *manager)
+{
+  const char * const vfl[] = {
+    "H:|-[button1(==button2)]-12-[button2]-|",
+    "H:|-[button3]-|",
+    "V:|-[button1]-12-[button3(==button1)]-|",
+    "V:|-[button2]-12-[button3(==button2)]-|",
+  };
+  GError *error = NULL;
+
+  gtk_constraint_layout_add_constraints_from_description (manager, vfl, G_N_ELEMENTS (vfl),
+                                                          8, 8,
+                                                          &error,
+                                                          "button1", self->button1,
+                                                          "button2", self->button2,
+                                                          "button3", self->button3,
+                                                          NULL);
+  if (error != NULL)
+    {
+      g_printerr ("VFL parsing error:\n%s", error->message);
+      g_error_free (error);
+    }
+}
+
+static void
+vfl_grid_init (VflGrid *self)
+{
+  GtkWidget *widget = GTK_WIDGET (self);
+
+  self->button1 = gtk_button_new_with_label ("Child 1");
+  gtk_widget_set_parent (self->button1, widget);
+  gtk_widget_set_name (self->button1, "button1");
+
+  self->button2 = gtk_button_new_with_label ("Child 2");
+  gtk_widget_set_parent (self->button2, widget);
+  gtk_widget_set_name (self->button2, "button2");
+
+  self->button3 = gtk_button_new_with_label ("Child 3");
+  gtk_widget_set_parent (self->button3, widget);
+  gtk_widget_set_name (self->button3, "button3");
+
+  GtkLayoutManager *manager = gtk_widget_get_layout_manager (GTK_WIDGET (self));
+  build_constraints (self, GTK_CONSTRAINT_LAYOUT (manager));
+}
+
+GtkWidget *
+do_constraints3 (GtkWidget *do_widget)
+{
+ static GtkWidget *window;
+
+ if (!window)
+   {
+     GtkWidget *header, *box, *grid, *button;
+
+     window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
+     gtk_window_set_display (GTK_WINDOW (window), gtk_widget_get_display (do_widget));
+
+     header = gtk_header_bar_new ();
+     gtk_header_bar_set_title (GTK_HEADER_BAR (header), "Constraints");
+     gtk_header_bar_set_show_title_buttons (GTK_HEADER_BAR (header), FALSE);
+     gtk_window_set_titlebar (GTK_WINDOW (window), header);
+     g_signal_connect (window, "destroy",
+                       G_CALLBACK (gtk_widget_destroyed), &window);
+
+     box = gtk_box_new (GTK_ORIENTATION_VERTICAL, 12);
+     gtk_container_add (GTK_CONTAINER (window), box);
+
+     grid = g_object_new (vfl_grid_get_type (), NULL);
+     gtk_widget_set_hexpand (grid, TRUE);
+     gtk_widget_set_vexpand (grid, TRUE);
+     gtk_container_add (GTK_CONTAINER (box), grid);
+
+     button = gtk_button_new_with_label ("Close");
+     gtk_container_add (GTK_CONTAINER (box), button);
+     gtk_widget_set_hexpand (grid, TRUE);
+     g_signal_connect_swapped (button, "clicked",
+                               G_CALLBACK (gtk_widget_destroy), window);
+   }
+
+ if (!gtk_widget_get_visible (window))
+   gtk_widget_show (window);
+ else
+   gtk_widget_destroy (window);
+
+ return window;
+}

demos/gtk-demo/demo.gresource.xml

@@ -150,6 +150,9 @@
     <file>clipboard.c</file>
     <file>colorsel.c</file>
     <file>combobox.c</file>
+    <file>constraints.c</file>
+    <file>constraints2.c</file>
+    <file>constraints3.c</file>
     <file>css_accordion.c</file>
     <file>css_basics.c</file>
     <file>css_blendmodes.c</file>

demos/gtk-demo/fishbowl.c

@@ -306,6 +306,7 @@ do_fishbowl (GtkWidget *do_widget)
                         G_CALLBACK (gtk_widget_destroyed), &window);
 
       gtk_widget_realize (window);
+      g_object_unref (builder);
     }
 
   if (!gtk_widget_get_visible (window))

demos/gtk-demo/meson.build

@@ -8,6 +8,9 @@ demos = files([
   'clipboard.c',
   'colorsel.c',
   'combobox.c',
+  'constraints.c',
+  'constraints2.c',
+  'constraints3.c',
   'css_accordion.c',
   'css_basics.c',
   'css_blendmodes.c',

demos/meson.build

@@ -1,3 +1,4 @@
+subdir('constraint-editor')
 subdir('gtk-demo')
 subdir('icon-browser')
 subdir('node-editor')

demos/node-editor/node-editor-window.c

@@ -707,6 +707,14 @@ static void
 node_editor_window_unrealize (GtkWidget *widget)
 {
   NodeEditorWindow *self = NODE_EDITOR_WINDOW (widget);
+  guint i;
+
+  for (i = 0; i < g_list_model_get_n_items (G_LIST_MODEL (self->renderers)); i ++)
+    {
+      gpointer item = g_list_model_get_item (G_LIST_MODEL (self->renderers), i);
+      gsk_renderer_unrealize (gtk_renderer_paintable_get_renderer (item));
+      g_object_unref (item);
+    }
 
   g_list_store_remove_all (self->renderers);
 

demos/widget-factory/widget-factory.c

@@ -1405,8 +1405,10 @@ text_view_add_to_context_menu (GtkTextView *text_view)
   item = g_menu_item_new (_("Underline"), "format.underline");
   g_menu_item_set_attribute (item, "touch-icon", "s", "format-text-underline-symbolic");
   g_menu_append_item (G_MENU (menu), item);
+  g_object_unref (item);
 
   gtk_text_view_set_extra_menu (text_view, G_MENU_MODEL (menu));
+  g_object_unref (menu);
 
   g_signal_connect (gtk_text_view_get_buffer (text_view), "changed", G_CALLBACK (text_changed), NULL);
   g_signal_connect (gtk_text_view_get_buffer (text_view), "mark-set", G_CALLBACK (text_changed), NULL);
@@ -1707,7 +1709,7 @@ activate (GApplication *app)
   gtk_css_provider_load_from_resource (provider, "/org/gtk/WidgetFactory4/widget-factory.css");
   gtk_style_context_add_provider_for_display (gdk_display_get_default (),
                                               GTK_STYLE_PROVIDER (provider),
-                                              GTK_STYLE_PROVIDER_PRIORITY_USER);
+                                              GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);
   g_object_unref (provider);
 
   builder = gtk_builder_new_from_resource ("/org/gtk/WidgetFactory4/widget-factory.ui");

docs/reference/gdk/meson.build

@@ -99,7 +99,7 @@ if wayland_enabled
   src_dir += [ gdkwayland_inc ]
 endif
 
-if get_option('documentation')
+if get_option('gtk_doc')
   configure_file(input: 'version.xml.in', output: 'version.xml', configuration: version_conf)
 
   gnome.gtkdoc('gdk4',

docs/reference/gsk/meson.build

@@ -34,7 +34,7 @@ private_headers = [
 images = [
 ]
 
-if get_option('documentation')
+if get_option('gtk_doc')
   configure_file(input: 'version.xml.in', output: 'version.xml', configuration: version_conf)
 
   gnome.gtkdoc('gsk4',

docs/reference/gtk/building.sgml

@@ -355,8 +355,8 @@ How to compile GTK itself
           </group>
           <sbr/>
           <group>
-            <arg choice="plain">-Ddocumentation=true</arg>
-            <arg choice="plain">-Ddocumentation=false</arg>
+            <arg choice="plain">-Dgtk_doc=true</arg>
+            <arg choice="plain">-Dgtk_doc=false</arg>
           </group>
           <sbr/>
           <group>
@@ -382,7 +382,7 @@ How to compile GTK itself
       </formalpara>
 
       <formalpara>
-        <title><systemitem>documentation</systemitem> and
+        <title><systemitem>gtk_doc</systemitem> and
           <systemitem>man-pages</systemitem></title>
 
         <para>
@@ -394,7 +394,7 @@ How to compile GTK itself
           <application>gtk-doc</application> installed and
           are modifying GTK, you may want to enable
           <application>gtk-doc</application> support by passing
-          in <systemitem>documentation</systemitem>.
+          in <systemitem>gtk_doc</systemitem>.
         </para>
         <para>
           Additionally, some tools provided by GTK have their own

docs/reference/gtk/gtk4-docs.xml

@@ -109,6 +109,9 @@
       <xi:include href="xml/gtkcustomlayout.xml" />
       <xi:include href="xml/gtkfixedlayout.xml" />
       <xi:include href="xml/gtkgridlayout.xml" />
+      <xi:include href="xml/gtkconstraintlayout.xml" />
+      <xi:include href="xml/gtkconstraint.xml" />
+      <xi:include href="xml/gtkconstraintguide.xml" />
     </chapter>
 
     <chapter id="DisplayWidgets">

docs/reference/gtk/gtk4-sections.txt

@@ -4432,7 +4432,6 @@ gtk_widget_realize
 gtk_widget_unrealize
 gtk_widget_queue_draw
 gtk_widget_queue_resize
-gtk_widget_queue_resize_no_redraw
 gtk_widget_queue_allocate
 gtk_widget_get_frame_clock
 gtk_widget_get_scale_factor
@@ -4604,7 +4603,6 @@ gtk_widget_get_vexpand
 gtk_widget_set_vexpand
 gtk_widget_get_vexpand_set
 gtk_widget_set_vexpand_set
-gtk_widget_queue_compute_expand
 gtk_widget_compute_expand
 
 <SUBSECTION Templates>
@@ -7287,3 +7285,87 @@ gtk_grid_layout_get_type
 GTK_TYPE_GRID_LAYOUT_CHILD
 gtk_grid_layout_child_get_type
 </SECTION>
+
+<SECTION>
+<FILE>gtkconstraint</FILE>
+GtkConstraint
+GtkConstraintTarget
+
+gtk_constraint_new
+gtk_constraint_new_constant
+gtk_constraint_get_target
+GtkConstraintAttribute
+gtk_constraint_get_target_attribute
+GtkConstraintRelation
+gtk_constraint_get_relation
+gtk_constraint_get_source
+gtk_constraint_get_source_attribute
+gtk_constraint_get_multiplier
+gtk_constraint_get_constant
+GtkConstraintStrength
+gtk_constraint_get_strength
+gtk_constraint_is_required
+gtk_constraint_is_attached
+gtk_constraint_is_constant
+
+<SUBSECTION Standard>
+GTK_TYPE_CONSTRAINT
+gtk_constraint_get_type
+GTK_TYPE_CONSTRAINT_TARGET
+gtk_constraint_target_get_type
+</SECTION>
+
+<SECTION>
+<FILE>gtkconstraintlayout</FILE>
+GtkConstraintLayout
+GtkConstraintLayoutChild
+GtkConstraintVflParserError
+
+gtk_constraint_layout_new
+
+<SUBSECTION Constraints>
+gtk_constraint_layout_add_constraint
+gtk_constraint_layout_remove_constraint
+gtk_constraint_layout_remove_all_constraints
+
+<SUBSECTION Guides>
+gtk_constraint_layout_add_guide
+gtk_constraint_layout_remove_guide
+
+<SUBSECTION VFL>
+gtk_constraint_layout_add_constraints_from_description
+gtk_constraint_layout_add_constraints_from_descriptionv
+
+<SUBSECTION>
+gtk_constraint_layout_observe_constraints
+gtk_constraint_layout_observe_guides
+
+<SUBSECTION Standard>
+GTK_TYPE_CONSTRAINT_LAYOUT
+gtk_constraint_layout_get_type
+GTK_TYPE_CONSTRAINT_LAYOUT_CHILD
+gtk_constraint_layout_child_get_type
+GTK_CONSTRAINT_VFL_PARSER_ERROR
+gtk_constraint_vfl_parser_error_quark
+</SECTION>
+
+<SECTION>
+<FILE>gtkconstraintguide</FILE>
+GtkConstraintGuide
+
+gtk_constraint_guide_new
+gtk_constraint_guide_set_name
+gtk_constraint_guide_get_name
+gtk_constraint_guide_set_strength
+gtk_constraint_guide_get_strength
+gtk_constraint_guide_set_min_size
+gtk_constraint_guide_get_min_size
+gtk_constraint_guide_set_nat_size
+gtk_constraint_guide_get_nat_size
+gtk_constraint_guide_set_max_size
+gtk_constraint_guide_get_max_size
+
+<SUBSECTION Standard>
+GTK_TYPE_CONSTRAINT_GUIDE
+gtk_constraint_guide_get_tyoe
+</SECTION>

docs/reference/gtk/gtk4.types.in

@@ -49,6 +49,10 @@ gtk_color_chooser_dialog_get_type
 gtk_color_chooser_widget_get_type
 gtk_combo_box_get_type
 gtk_combo_box_text_get_type
+gtk_constraint_get_type
+gtk_constraint_guide_get_type
+gtk_constraint_layout_get_type
+gtk_constraint_target_get_type
 gtk_container_get_type
 gtk_css_provider_get_type
 gtk_dialog_get_type

docs/reference/gtk/meson.build

@@ -23,6 +23,13 @@ private_headers = [
   'gtkcolorswatchprivate.h',
   'gtkcomboboxprivate.h',
   'gtkcontainerprivate.h',
+  'gtkconstraintexpressionprivate.h',
+  'gtkconstraintguideprivate.h',
+  'gtkconstraintlayoutprivate.h',
+  'gtkconstraintprivate.h',
+  'gtkconstraintsolverprivate.h',
+  'gtkconstrainttypesprivate.h',
+  'gtkconstraintvflparserprivate.h',
   'gtkcssanimatedstyleprivate.h',
   'gtkcssanimationprivate.h',
   'gtkcssarrayvalueprivate.h',
@@ -394,7 +401,7 @@ else
   types_conf.set('DISABLE_ON_QUARTZ', '')
 endif
 
-if get_option('documentation')
+if get_option('gtk_doc')
   configure_file(input: 'version.xml.in', output: 'version.xml', configuration: version_conf)
   configure_file(input: 'getting_started.xml.in', output: 'getting_started.xml', configuration: src_dir_conf)
 

docs/reference/meson.build

@@ -1,4 +1,4 @@
-if get_option('documentation')
+if get_option('gtk_doc')
   glib_prefix = dependency('glib-2.0').get_pkgconfig_variable('prefix')
   glib_docpath = join_paths(glib_prefix, 'share', 'gtk-doc', 'html')
 

docs/tools/meson.build

@@ -1,4 +1,4 @@
-if x11_enabled and get_option('documentation')
+if x11_enabled and get_option('gtk_doc')
   doc_shooter_sources = [
     'shadow.c',
     'shooter.c',

gdk/broadway/gdksurface-broadway.c

@@ -88,10 +88,10 @@ gdk_broadway_surface_finalize (GObject *object)
 }
 
 static gboolean
-thaw_clock_cb (GdkFrameClock *clock)
+thaw_updates_cb (GdkSurface *surface)
 {
-  _gdk_frame_clock_thaw (clock);
-  g_object_unref (clock);
+  gdk_surface_thaw_updates (surface);
+  g_object_unref (surface);
   return G_SOURCE_REMOVE;
 }
 
@@ -109,9 +109,9 @@ _gdk_broadway_roundtrip_notify (GdkSurface  *surface,
 
   /* If there is no remote web client, rate limit update to once a second */
   if (local_reply)
-    g_timeout_add_seconds (1, (GSourceFunc)thaw_clock_cb, g_object_ref (clock));
+    g_timeout_add_seconds (1, (GSourceFunc)thaw_updates_cb, g_object_ref (surface));
   else
-    _gdk_frame_clock_thaw (clock);
+    gdk_surface_thaw_updates (surface);
 
   if (timings)
     {
@@ -140,7 +140,7 @@ on_frame_clock_after_paint (GdkFrameClock *clock,
   GdkBroadwayDisplay *broadway_display;
 
   impl->pending_frame_counter = gdk_frame_clock_get_frame_counter (clock);
-  _gdk_frame_clock_freeze (gdk_surface_get_frame_clock (surface));
+  gdk_surface_freeze_updates (surface);
 
   broadway_display = GDK_BROADWAY_DISPLAY (display);
 

gdk/gdkframeclock.c

@@ -97,10 +97,14 @@ struct _GdkFrameClockPrivate
   gint n_timings;
   gint current;
   GdkFrameTimings *timings[FRAME_HISTORY_MAX_LENGTH];
+  gint n_freeze_inhibitors;
 };
 
 G_DEFINE_ABSTRACT_TYPE_WITH_PRIVATE (GdkFrameClock, gdk_frame_clock, G_TYPE_OBJECT)
 
+static void
+_gdk_frame_clock_freeze (GdkFrameClock *clock);
+
 static void
 gdk_frame_clock_finalize (GObject *object)
 {
@@ -114,12 +118,21 @@ gdk_frame_clock_finalize (GObject *object)
   G_OBJECT_CLASS (gdk_frame_clock_parent_class)->finalize (object);
 }
 
+static void
+gdk_frame_clock_constructed (GObject *object)
+{
+  G_OBJECT_CLASS (gdk_frame_clock_parent_class)->constructed (object);
+
+  _gdk_frame_clock_freeze (GDK_FRAME_CLOCK (object));
+}
+
 static void
 gdk_frame_clock_class_init (GdkFrameClockClass *klass)
 {
   GObjectClass *gobject_class = (GObjectClass*) klass;
 
   gobject_class->finalize     = gdk_frame_clock_finalize;
+  gobject_class->constructed  = gdk_frame_clock_constructed;
 
   /**
    * GdkFrameClock::flush-events:
@@ -335,7 +348,7 @@ gdk_frame_clock_end_updating (GdkFrameClock *frame_clock)
   GDK_FRAME_CLOCK_GET_CLASS (frame_clock)->end_updating (frame_clock);
 }
 
-void
+static void
 _gdk_frame_clock_freeze (GdkFrameClock *clock)
 {
   g_return_if_fail (GDK_IS_FRAME_CLOCK (clock));
@@ -344,7 +357,7 @@ _gdk_frame_clock_freeze (GdkFrameClock *clock)
 }
 
 
-void
+static void
 _gdk_frame_clock_thaw (GdkFrameClock *clock)
 {
   g_return_if_fail (GDK_IS_FRAME_CLOCK (clock));
@@ -352,6 +365,35 @@ _gdk_frame_clock_thaw (GdkFrameClock *clock)
   GDK_FRAME_CLOCK_GET_CLASS (clock)->thaw (clock);
 }
 
+void
+_gdk_frame_clock_inhibit_freeze (GdkFrameClock *clock)
+{
+  GdkFrameClockPrivate *priv;
+
+  g_return_if_fail (GDK_IS_FRAME_CLOCK (clock));
+
+  priv = clock->priv;
+
+  priv->n_freeze_inhibitors++;
+  if (priv->n_freeze_inhibitors == 1)
+    _gdk_frame_clock_thaw (clock);
+}
+
+
+void
+_gdk_frame_clock_uninhibit_freeze (GdkFrameClock *clock)
+{
+  GdkFrameClockPrivate *priv;
+
+  g_return_if_fail (GDK_IS_FRAME_CLOCK (clock));
+
+  priv = clock->priv;
+
+  priv->n_freeze_inhibitors--;
+  if (priv->n_freeze_inhibitors == 0)
+    _gdk_frame_clock_freeze (clock);
+}
+
 /**
  * gdk_frame_clock_get_frame_counter:
  * @frame_clock: a #GdkFrameClock

gdk/gdkframeclockprivate.h

@@ -105,8 +105,8 @@ struct _GdkFrameTimings
   guint slept_before : 1;
 };
 
-void _gdk_frame_clock_freeze (GdkFrameClock *clock);
-void _gdk_frame_clock_thaw   (GdkFrameClock *clock);
+void _gdk_frame_clock_inhibit_freeze (GdkFrameClock *clock);
+void _gdk_frame_clock_uninhibit_freeze (GdkFrameClock *clock);
 
 void _gdk_frame_clock_begin_frame         (GdkFrameClock   *clock);
 void _gdk_frame_clock_debug_print_timings (GdkFrameClock   *clock,

gdk/gdksurface.c

@@ -1341,10 +1341,14 @@ gdk_surface_schedule_update (GdkSurface *surface)
 {
   GdkFrameClock *frame_clock;
 
-  if (surface &&
-      (surface->update_freeze_count ||
-       gdk_surface_is_toplevel_frozen (surface)))
-    return;
+  g_return_if_fail (surface);
+
+  if (surface->update_freeze_count ||
+      gdk_surface_is_toplevel_frozen (surface))
+    {
+      surface->pending_schedule_update = TRUE;
+      return;
+    }
 
   /* If there's no frame clock (a foreign surface), then the invalid
    * region will just stick around unless gdk_surface_process_updates()
@@ -1400,7 +1404,6 @@ gdk_surface_paint_on_clock (GdkFrameClock *clock,
                             void          *data)
 {
   GdkSurface *surface = GDK_SURFACE (data);
-  GList *l;
 
   g_return_if_fail (GDK_IS_SURFACE (surface));
 
@@ -1421,9 +1424,6 @@ gdk_surface_paint_on_clock (GdkFrameClock *clock,
       gdk_surface_remove_update_surface (surface);
     }
 
-  for (l = surface->children; l; l = l->next)
-    gdk_surface_paint_on_clock (clock, l->data);
-
   g_object_unref (surface);
 }
 
@@ -1581,13 +1581,17 @@ gdk_surface_freeze_updates (GdkSurface *surface)
   g_return_if_fail (GDK_IS_SURFACE (surface));
 
   surface->update_freeze_count++;
+  if (surface->update_freeze_count == 1)
+    _gdk_frame_clock_uninhibit_freeze (surface->frame_clock);
 }
 
 /**
  * gdk_surface_thaw_updates:
  * @surface: a #GdkSurface
  *
- * Thaws a surface frozen with gdk_surface_freeze_updates().
+ * Thaws a surface frozen with gdk_surface_freeze_updates(). Note that this
+ * will not necessarily schedule updates if the surface freeze count reaches
+ * zero.
  **/
 void
 gdk_surface_thaw_updates (GdkSurface *surface)
@@ -1597,7 +1601,15 @@ gdk_surface_thaw_updates (GdkSurface *surface)
   g_return_if_fail (surface->update_freeze_count > 0);
 
   if (--surface->update_freeze_count == 0)
-    gdk_surface_schedule_update (surface);
+    {
+      _gdk_frame_clock_inhibit_freeze (surface->frame_clock);
+
+      if (surface->pending_schedule_update)
+        {
+          surface->pending_schedule_update = FALSE;
+          gdk_surface_schedule_update (surface);
+        }
+    }
 }
 
 void
@@ -1606,7 +1618,7 @@ gdk_surface_freeze_toplevel_updates (GdkSurface *surface)
   g_return_if_fail (GDK_IS_SURFACE (surface));
 
   surface->update_and_descendants_freeze_count++;
-  _gdk_frame_clock_freeze (gdk_surface_get_frame_clock (surface));
+  gdk_surface_freeze_updates (surface);
 }
 
 void
@@ -1616,9 +1628,9 @@ gdk_surface_thaw_toplevel_updates (GdkSurface *surface)
   g_return_if_fail (surface->update_and_descendants_freeze_count > 0);
 
   surface->update_and_descendants_freeze_count--;
-  _gdk_frame_clock_thaw (gdk_surface_get_frame_clock (surface));
-
   gdk_surface_schedule_update (surface);
+  gdk_surface_thaw_updates (surface);
+
 }
 
 /**
@@ -3703,40 +3715,42 @@ gdk_surface_set_frame_clock (GdkSurface     *surface,
   if (clock)
     {
       g_object_ref (clock);
-      if (surface->parent == NULL)
-        {
-          g_signal_connect (G_OBJECT (clock),
-                            "flush-events",
-                            G_CALLBACK (gdk_surface_flush_events),
-                            surface);
-          g_signal_connect (G_OBJECT (clock),
-                            "resume-events",
-                            G_CALLBACK (gdk_surface_resume_events),
-                            surface);
-          g_signal_connect (G_OBJECT (clock),
-                            "paint",
-                            G_CALLBACK (gdk_surface_paint_on_clock),
-                            surface);
-        }
+
+      g_signal_connect (G_OBJECT (clock),
+                        "flush-events",
+                        G_CALLBACK (gdk_surface_flush_events),
+                        surface);
+      g_signal_connect (G_OBJECT (clock),
+                        "resume-events",
+                        G_CALLBACK (gdk_surface_resume_events),
+                        surface);
+      g_signal_connect (G_OBJECT (clock),
+                        "paint",
+                        G_CALLBACK (gdk_surface_paint_on_clock),
+                        surface);
+
+      if (surface->update_freeze_count == 0)
+        _gdk_frame_clock_inhibit_freeze (clock);
     }
 
   if (surface->frame_clock)
     {
-      if (surface->parent == NULL)
-        {
-          if (surface->frame_clock_events_paused)
-            gdk_surface_resume_events (surface->frame_clock, G_OBJECT (surface));
+      if (surface->frame_clock_events_paused)
+        gdk_surface_resume_events (surface->frame_clock, G_OBJECT (surface));
+
+      g_signal_handlers_disconnect_by_func (G_OBJECT (surface->frame_clock),
+                                            G_CALLBACK (gdk_surface_flush_events),
+                                            surface);
+      g_signal_handlers_disconnect_by_func (G_OBJECT (surface->frame_clock),
+                                            G_CALLBACK (gdk_surface_resume_events),
+                                            surface);
+      g_signal_handlers_disconnect_by_func (G_OBJECT (surface->frame_clock),
+                                            G_CALLBACK (gdk_surface_paint_on_clock),
+                                            surface);
+
+      if (surface->update_freeze_count == 0)
+        _gdk_frame_clock_uninhibit_freeze (surface->frame_clock);
 
-          g_signal_handlers_disconnect_by_func (G_OBJECT (surface->frame_clock),
-                                                G_CALLBACK (gdk_surface_flush_events),
-                                                surface);
-          g_signal_handlers_disconnect_by_func (G_OBJECT (surface->frame_clock),
-                                                G_CALLBACK (gdk_surface_resume_events),
-                                                surface);
-          g_signal_handlers_disconnect_by_func (G_OBJECT (surface->frame_clock),
-                                                G_CALLBACK (gdk_surface_paint_on_clock),
-                                                surface);
-        }
       g_object_unref (surface->frame_clock);
     }
 

gdk/gdksurfaceprivate.h

@@ -49,6 +49,7 @@ struct _GdkSurface
 
   cairo_region_t *update_area;
   guint update_freeze_count;
+  gboolean pending_schedule_update;
   /* This is the update_area that was in effect when the current expose
      started. It may be smaller than the expose area if we'e painting
      more than we have to, but it represents the "true" damage. */

gdk/wayland/gdksurface-wayland.c

@@ -349,7 +349,7 @@ frame_callback (void               *data,
     return;
 
   impl->awaiting_frame = FALSE;
-  _gdk_frame_clock_thaw (clock);
+  gdk_surface_thaw_updates (surface);
 
   timings = gdk_frame_clock_get_timings (clock, impl->pending_frame_counter);
   impl->pending_frame_counter = 0;
@@ -465,8 +465,9 @@ on_frame_clock_after_paint (GdkFrameClock *clock,
       g_signal_emit (impl, signals[COMMITTED], 0);
     }
 
-  if (impl->awaiting_frame)
-    _gdk_frame_clock_freeze (clock);
+  if (impl->awaiting_frame &&
+      impl->pending_frame_counter == gdk_frame_clock_get_frame_counter (clock))
+    gdk_surface_freeze_updates (surface);
 }
 
 void
@@ -2577,12 +2578,8 @@ gdk_wayland_surface_hide_surface (GdkSurface *surface)
 
       if (impl->awaiting_frame)
         {
-          GdkFrameClock *frame_clock;
-
           impl->awaiting_frame = FALSE;
-          frame_clock = gdk_surface_get_frame_clock (surface);
-          if (frame_clock)
-            _gdk_frame_clock_thaw (frame_clock);
+          gdk_surface_thaw_updates (surface);
         }
 
       if (impl->display_server.gtk_surface)

gdk/x11/gdkdisplay-x11.c

@@ -874,7 +874,7 @@ gdk_x11_display_translate_event (GdkEventTranslator *translator,
               surface_impl->toplevel->frame_pending)
             {
               surface_impl->toplevel->frame_pending = FALSE;
-              _gdk_frame_clock_thaw (gdk_surface_get_frame_clock (event->any.surface));
+              gdk_surface_thaw_updates (event->any.surface);
             }
 
 	  if (toplevel)
@@ -1238,7 +1238,7 @@ _gdk_wm_protocols_filter (const XEvent *xevent,
           if (surface_impl->toplevel->frame_pending)
             {
               surface_impl->toplevel->frame_pending = FALSE;
-              _gdk_frame_clock_thaw (clock);
+              gdk_surface_thaw_updates (event->any.surface);
             }
 
           gdk_frame_clock_get_refresh_info (clock,

gdk/x11/gdkselectionoutputstream-x11.c

@@ -503,6 +503,7 @@ gdk_x11_selection_output_stream_invoke_close (gpointer stream)
   g_signal_handlers_disconnect_by_func (priv->display,
                                         gdk_x11_selection_output_stream_xevent,
                                         stream);
+  g_object_unref (stream);
 
   return G_SOURCE_REMOVE;
 }
@@ -512,7 +513,7 @@ gdk_x11_selection_output_stream_close (GOutputStream  *stream,
                                        GCancellable   *cancellable,
                                        GError        **error)
 {
-  g_main_context_invoke (NULL, gdk_x11_selection_output_stream_invoke_close, stream);
+  g_main_context_invoke (NULL, gdk_x11_selection_output_stream_invoke_close, g_object_ref (stream));
 
   return TRUE;
 }

gdk/x11/gdksurface-x11.c

@@ -397,7 +397,7 @@ gdk_x11_surface_end_frame (GdkSurface *surface)
 					       g_intern_static_string ("_NET_WM_FRAME_DRAWN")))
         {
           impl->toplevel->frame_pending = TRUE;
-          _gdk_frame_clock_freeze (gdk_surface_get_frame_clock (surface));
+          gdk_surface_freeze_updates (surface);
           timings->cookie = impl->toplevel->current_counter_value;
         }
     }

gsk/gl/gskglglyphcache.c

@@ -193,10 +193,10 @@ upload_glyph (GlyphCacheKey    *key,
   if (render_glyph (key, value, &r))
     {
       glBindTexture (GL_TEXTURE_2D, value->texture_id);
-      glTextureSubImage2D (value->texture_id, 0,
-                           r.x, r.y, r.width, r.height,
-                           GL_BGRA, GL_UNSIGNED_INT_8_8_8_8_REV,
-                           r.data);
+      glTexSubImage2D (GL_TEXTURE_2D, 0,
+                       r.x, r.y, r.width, r.height,
+                       GL_BGRA, GL_UNSIGNED_INT_8_8_8_8_REV,
+                       r.data);
       g_free (r.data);
     }
 

gsk/gl/gskgliconcache.c

@@ -136,7 +136,7 @@ upload_region_or_else (GskGLIconCache *self,
                        GskImageRegion *region)
 {
   glBindTexture (GL_TEXTURE_2D, texture_id);
-  glTextureSubImage2D (texture_id, 0, region->x, region->y, region->width, region->height,
+  glTexSubImage2D (GL_TEXTURE_2D, 0, region->x, region->y, region->width, region->height,
                    GL_BGRA, GL_UNSIGNED_INT_8_8_8_8_REV, region->data);
 }
 

gsk/gl/gskglrenderer.c

@@ -808,7 +808,8 @@ upload_texture (GskGLRenderer *self,
   int texture_id;
 
   if (texture->width <= 128 &&
-      texture->height <= 128)
+      texture->height <= 128 &&
+      !GDK_IS_GL_TEXTURE (texture))
     {
       graphene_rect_t trect;
 
@@ -943,11 +944,9 @@ render_transform_node (GskGLRenderer   *self,
     case GSK_TRANSFORM_CATEGORY_2D:
     default:
       {
-        graphene_matrix_t mat;
 
         if (node_supports_transform (child))
           {
-            gsk_transform_to_matrix (node_transform, &mat);
             ops_push_modelview (builder, node_transform);
             gsk_gl_renderer_add_render_ops (self, child, builder);
             ops_pop_modelview (builder);
@@ -972,7 +971,6 @@ render_transform_node (GskGLRenderer   *self,
                                &region, &is_offscreen,
                                RESET_CLIP | RESET_OPACITY);
 
-            gsk_transform_to_matrix (node_transform, &mat);
             ops_push_modelview (builder, node_transform);
             ops_set_texture (builder, region.texture_id);
             ops_set_program (builder, &self->blit_program);
@@ -1017,12 +1015,49 @@ render_opacity_node (GskGLRenderer   *self,
                      GskRenderNode   *node,
                      RenderOpBuilder *builder)
 {
+  GskRenderNode *child = gsk_opacity_node_get_child (node);
+  const float opacity = gsk_opacity_node_get_opacity (node);
   float prev_opacity;
 
-  prev_opacity = ops_set_opacity (builder,
-                                  builder->current_opacity * gsk_opacity_node_get_opacity (node));
+  if (gsk_render_node_get_node_type (child) == GSK_CONTAINER_NODE)
+    {
+      const float min_x = builder->dx + node->bounds.origin.x;
+      const float min_y = builder->dy + node->bounds.origin.y;
+      const float max_x = min_x + node->bounds.size.width;
+      const float max_y = min_y + node->bounds.size.height;
+      gboolean is_offscreen;
+      TextureRegion region;
 
-  gsk_gl_renderer_add_render_ops (self, gsk_opacity_node_get_child (node), builder);
+      /* The semantics of an opacity node mandate that when, e.g., two color nodes overlap,
+       * there may not be any blending between them */
+      add_offscreen_ops (self, builder, &child->bounds,
+                         child,
+                         &region, &is_offscreen,
+                         FORCE_OFFSCREEN | RESET_OPACITY | RESET_CLIP);
+
+      prev_opacity = ops_set_opacity (builder,
+                                      builder->current_opacity * opacity);
+
+      ops_set_program (builder, &self->blit_program);
+      ops_set_texture (builder, region.texture_id);
+
+      ops_draw (builder, (GskQuadVertex[GL_N_VERTICES]) {
+        { { min_x, min_y }, { region.x,  region.y2 }, },
+        { { min_x, max_y }, { region.x,  region.y  }, },
+        { { max_x, min_y }, { region.x2, region.y2 }, },
+
+        { { max_x, max_y }, { region.x2, region.y  }, },
+        { { min_x, max_y }, { region.x,  region.y  }, },
+        { { max_x, min_y }, { region.x2, region.y2 }, },
+      });
+    }
+  else
+    {
+      prev_opacity = ops_set_opacity (builder,
+                                      builder->current_opacity * opacity);
+
+      gsk_gl_renderer_add_render_ops (self, child, builder);
+    }
 
   ops_set_opacity (builder, prev_opacity);
 }
@@ -1292,7 +1327,7 @@ render_rounded_clip_node (GskGLRenderer       *self,
         { { min_x, min_y }, { 0, 1 }, },
         { { min_x, max_y }, { 0, 0 }, },
         { { max_x, min_y }, { 1, 1 }, },
- 
+
         { { max_x, max_y }, { 1, 0 }, },
         { { min_x, max_y }, { 0, 0 }, },
         { { max_x, min_y }, { 1, 1 }, },
@@ -1393,7 +1428,7 @@ render_blur_node (GskGLRenderer       *self,
   ops_set_program (builder, &self->blur_program);
   op.op = OP_CHANGE_BLUR;
   graphene_size_init_from_size (&op.blur.size, &node->bounds.size);
-  op.blur.radius = gsk_blur_node_get_radius (node);
+  op.blur.radius = blur_radius;
   ops_add (builder, &op);
 
   ops_set_texture (builder, region.texture_id);
@@ -1404,7 +1439,7 @@ render_blur_node (GskGLRenderer       *self,
         { { min_x, min_y }, { 0, 1 }, },
         { { min_x, max_y }, { 0, 0 }, },
         { { max_x, min_y }, { 1, 1 }, },
- 
+
         { { max_x, max_y }, { 1, 0 }, },
         { { min_x, max_y }, { 0, 0 }, },
         { { max_x, min_y }, { 1, 1 }, },
@@ -1855,10 +1890,10 @@ render_shadow_node (GskGLRenderer       *self,
                     RenderOpBuilder     *builder,
                     const GskQuadVertex *vertex_data)
 {
-  float min_x = node->bounds.origin.x;
-  float min_y = node->bounds.origin.y;
-  float max_x = min_x + node->bounds.size.width;
-  float max_y = min_y + node->bounds.size.height;
+  float min_x;
+  float min_y;
+  float max_x;
+  float max_y;
   GskRenderNode *original_child = gsk_shadow_node_get_child (node);
   GskRenderNode *shadow_child = original_child;
   gsize n_shadows = gsk_shadow_node_get_n_shadows (node);
@@ -1884,6 +1919,11 @@ render_shadow_node (GskGLRenderer       *self,
       shadow_child = gsk_color_matrix_node_get_child (shadow_child);
     }
 
+  min_x = builder->dx + shadow_child->bounds.origin.x;
+  min_y = builder->dy + shadow_child->bounds.origin.y;
+  max_x = min_x + shadow_child->bounds.size.width;
+  max_y = min_y + shadow_child->bounds.size.height;
+
   for (i = 0; i < n_shadows; i ++)
     {
       const GskShadow *shadow = gsk_shadow_node_peek_shadow (node, i);
@@ -1905,11 +1945,6 @@ render_shadow_node (GskGLRenderer       *self,
       if (gdk_rgba_is_clear (&shadow->color))
         continue;
 
-      min_x = builder->dx + shadow_child->bounds.origin.x;
-      min_y = builder->dy + shadow_child->bounds.origin.y;
-      max_x = min_x + shadow_child->bounds.size.width;
-      max_y = min_y + shadow_child->bounds.size.height;
-
       /* Draw the child offscreen, without the offset. */
       add_offscreen_ops (self, builder,
                          &shadow_child->bounds,
@@ -2344,6 +2379,7 @@ gsk_gl_renderer_dispose (GObject *gobject)
   GskGLRenderer *self = GSK_GL_RENDERER (gobject);
 
   g_clear_pointer (&self->render_ops, g_array_unref);
+  ops_free (&self->op_builder);
 
   G_OBJECT_CLASS (gsk_gl_renderer_parent_class)->dispose (gobject);
 }
@@ -3160,7 +3196,7 @@ gsk_gl_renderer_do_render (GskRenderer           *renderer,
                            int                    scale_factor)
 {
   GskGLRenderer *self = GSK_GL_RENDERER (renderer);
-  graphene_matrix_t modelview, projection;
+  graphene_matrix_t projection;
   gsize buffer_size;
 #ifdef G_ENABLE_DEBUG
   GskProfiler *profiler;
@@ -3180,7 +3216,6 @@ gsk_gl_renderer_do_render (GskRenderer           *renderer,
   g_assert (gsk_gl_driver_in_frame (self->gl_driver));
 
   /* Set up the modelview and projection matrices to fit our viewport */
-  graphene_matrix_init_scale (&modelview, scale_factor, scale_factor, 1.0);
   graphene_matrix_init_ortho (&projection,
                               viewport->origin.x,
                               viewport->origin.x + viewport->size.width,

gsk/gl/gskglrenderops.c

@@ -187,6 +187,17 @@ ops_init (RenderOpBuilder *builder)
     }
 }
 
+void
+ops_free (RenderOpBuilder *builder)
+{
+  int i;
+
+  for (i = 0; i < GL_N_PROGRAMS; i ++)
+    {
+      gsk_transform_unref (builder->program_state[i].modelview);
+    }
+}
+
 void
 ops_set_program (RenderOpBuilder *builder,
                  const Program   *program)
@@ -225,6 +236,7 @@ ops_set_program (RenderOpBuilder *builder,
       op.op = OP_CHANGE_MODELVIEW;
       gsk_transform_to_matrix (builder->current_modelview, &op.modelview);
       g_array_append_val (builder->render_ops, op);
+      gsk_transform_unref (program_state->modelview);
       program_state->modelview = gsk_transform_ref (builder->current_modelview);
     }
 
@@ -339,9 +351,12 @@ ops_set_modelview_internal (RenderOpBuilder *builder,
   RenderOp op;
   graphene_matrix_t matrix;
 
+#if 0
+  XXX This is not possible if we want pop() to work.
   if (builder->current_program &&
       gsk_transform_equal (builder->current_program_state->modelview, transform))
     return;
+#endif
 
   gsk_transform_to_matrix (transform, &matrix);
 

gsk/gl/gskglrenderopsprivate.h

@@ -290,6 +290,7 @@ void              ops_dump_framebuffer   (RenderOpBuilder         *builder,
                                           int                      width,
                                           int                      height);
 void              ops_init               (RenderOpBuilder         *builder);
+void              ops_free               (RenderOpBuilder         *builder);
 void              ops_push_debug_group    (RenderOpBuilder         *builder,
                                            const char              *text);
 void              ops_pop_debug_group     (RenderOpBuilder         *builder);

gsk/gskrendernodeimpl.c

@@ -1966,14 +1966,14 @@ gsk_transform_node_diff (GskRenderNode  *node1,
             cairo_region_t *tmp = cairo_region_copy (sub);
             cairo_region_translate (tmp, 1, 0);
             cairo_region_union (sub, tmp);
-            cairo_region_destroy (sub);
+            cairo_region_destroy (tmp);
           }
         if (floor (dy) != dy)
           {
             cairo_region_t *tmp = cairo_region_copy (sub);
             cairo_region_translate (tmp, 0, 1);
             cairo_region_union (sub, tmp);
-            cairo_region_destroy (sub);
+            cairo_region_destroy (tmp);
           }
         cairo_region_union (region, sub);
         cairo_region_destroy (sub);

gsk/gskrendernodeparser.c

@@ -94,6 +94,7 @@ parse_texture (GtkCssParser *parser,
       if (bytes)
         {
           stream = g_memory_input_stream_new_from_bytes (bytes);
+          g_bytes_unref (bytes);
           pixbuf = gdk_pixbuf_new_from_stream (stream, NULL, &error);
           g_object_unref (stream);
           if (pixbuf != NULL)
@@ -748,6 +749,8 @@ parse_glyphs (GtkCssParser *parser,
               pango_glyph_string_set_size (glyph_string, glyph_string->num_glyphs + 1);
               glyph_string->glyphs[glyph_string->num_glyphs - 1] = gi;
             }
+
+          g_free (s);
         }
       else
         {
@@ -817,7 +820,7 @@ parse_container_node (GtkCssParser *parser)
        token = gtk_css_parser_get_token (parser))
     {
       node = NULL;
-      /* We don't wand a semicolon here, but the parse_node function will figure
+      /* We don't want a semicolon here, but the parse_node function will figure
        * that out itself and return an error if we encounter one.
        */
       gtk_css_parser_start_semicolon_block (parser, GTK_CSS_TOKEN_OPEN_CURLY);

gsk/gsktransform.c

@@ -646,7 +646,7 @@ gsk_transform_translate_3d (GskTransform             *next,
   GskTranslateTransform *result;
 
   if (graphene_point3d_equal (point, graphene_point3d_zero ()))
-    return gsk_transform_ref (next);
+    return next;
 
   if (gsk_transform_has_class (next, &GSK_TRANSLATE_TRANSFORM_CLASS))
     {
@@ -801,7 +801,7 @@ gsk_transform_rotate (GskTransform *next,
   GskRotateTransform *result;
 
   if (angle == 0.0f)
-    return gsk_transform_ref (next);
+    return next;
 
   if (gsk_transform_has_class (next, &GSK_ROTATE_TRANSFORM_CLASS))
     {
@@ -932,7 +932,7 @@ gsk_transform_rotate_3d (GskTransform          *next,
     return gsk_transform_rotate (next, angle);
 
   if (angle == 0.0f)
-    return gsk_transform_ref (next);
+    return next;
 
   result = gsk_transform_alloc (&GSK_ROTATE3D_TRANSFORM_CLASS,
                                 GSK_TRANSFORM_CATEGORY_3D,
@@ -1121,7 +1121,7 @@ gsk_transform_scale_3d (GskTransform *next,
   GskScaleTransform *result;
 
   if (factor_x == 1 && factor_y == 1 && factor_z == 1)
-    return gsk_transform_ref (next);
+    return next;
 
   if (gsk_transform_has_class (next, &GSK_SCALE_TRANSFORM_CLASS))
     {
@@ -1250,7 +1250,7 @@ gsk_transform_perspective (GskTransform *next,
                            float         depth)
 {
   GskPerspectiveTransform *result;
-  
+
   if (gsk_transform_has_class (next, &GSK_PERSPECTIVE_TRANSFORM_CLASS))
     {
       GskTransform *r = gsk_transform_perspective (gsk_transform_ref (next->next),
@@ -1690,11 +1690,26 @@ gsk_transform_transform_bounds (GskTransform          *self,
       }
     break;
 
+    case GSK_TRANSFORM_CATEGORY_2D_AFFINE:
+      {
+        float dx, dy, scale_x, scale_y;
+
+        gsk_transform_to_affine (self, &scale_x, &scale_y, &dx, &dy);
+
+        *out_rect = *rect;
+        out_rect->origin.x *= scale_x;
+        out_rect->origin.y *= scale_y;
+        out_rect->size.width *= scale_x;
+        out_rect->size.height *= scale_y;
+        out_rect->origin.x += dx;
+        out_rect->origin.y += dy;
+      }
+    break;
+
     case GSK_TRANSFORM_CATEGORY_UNKNOWN:
     case GSK_TRANSFORM_CATEGORY_ANY:
     case GSK_TRANSFORM_CATEGORY_3D:
     case GSK_TRANSFORM_CATEGORY_2D:
-    case GSK_TRANSFORM_CATEGORY_2D_AFFINE:
     default:
       {
         graphene_matrix_t mat;
@@ -1886,18 +1901,43 @@ gsk_transform_parser_parse (GtkCssParser  *parser,
 
           transform = gsk_transform_translate_3d (transform, &GRAPHENE_POINT3D_INIT (0.f, 0.f, f[0]));
         }
-#if 0
-      /* FIXME: add these */
       else if (gtk_css_token_is_function (token, "skew"))
         {
+          graphene_matrix_t matrix;
+
+          if (!gtk_css_parser_consume_function (parser, 2, 2, gsk_transform_parse_float, f))
+            goto fail;
+
+          f[0] = f[0] / 180.0 * G_PI;
+          f[1] = f[1] / 180.0 * G_PI;
+
+          graphene_matrix_init_skew (&matrix, f[0], f[1]);
+          transform = gsk_transform_matrix (transform, &matrix);
         }
       else if (gtk_css_token_is_function (token, "skewX"))
         {
+          graphene_matrix_t matrix;
+
+          if (!gtk_css_parser_consume_function (parser, 1, 1, gsk_transform_parse_float, f))
+            goto fail;
+
+          f[0] = f[0] / 180.0 * G_PI;
+
+          graphene_matrix_init_skew (&matrix, f[0], 0);
+          transform = gsk_transform_matrix (transform, &matrix);
         }
       else if (gtk_css_token_is_function (token, "skewY"))
         {
+          graphene_matrix_t matrix;
+
+          if (!gtk_css_parser_consume_function (parser, 1, 1, gsk_transform_parse_float, f))
+            goto fail;
+
+          f[0] = f[0] / 180.0 * G_PI;
+
+          graphene_matrix_init_skew (&matrix, 0, f[0]);
+          transform = gsk_transform_matrix (transform, &matrix);
         }
-#endif
       else
         {
           break;

gsk/resources/glsl/blend.fs.glsl

@@ -4,14 +4,14 @@ uniform sampler2D u_source2;
 float
 combine (float source, float backdrop)
 {
-  return source + backdrop * (1 - source);
+  return source + backdrop * (1.0 - source);
 }
 
 vec4
 composite (vec4 Cs, vec4 Cb, vec3 B)
 {
-  float ao = Cs.a + Cb.a * (1 - Cs.a);
-  vec3 Co = (Cs.a*(1 - Cb.a)*Cs.rgb + Cs.a*Cb.a*B + (1 - Cs.a)*Cb.a*Cb.rgb) / ao;
+  float ao = Cs.a + Cb.a * (1.0 - Cs.a);
+  vec3 Co = (Cs.a*(1.0 - Cb.a)*Cs.rgb + Cs.a*Cb.a*B + (1.0 - Cs.a)*Cb.a*Cb.rgb) / ao;
   return vec4(Co, ao);
 }
 
@@ -43,9 +43,9 @@ float
 hard_light (float source, float backdrop)
 {
   if (source <= 0.5)
-    return 2 * backdrop * source;
+    return 2.0 * backdrop * source;
   else
-    return 2 * (backdrop + source - backdrop * source) - 1;
+    return 2.0 * (backdrop + source - backdrop * source) - 1.0;
 }
 
 vec4
@@ -63,14 +63,14 @@ soft_light (float source, float backdrop)
   float db;
 
   if (backdrop <= 0.25)
-    db = ((16 * backdrop - 12) * backdrop + 4) * backdrop;
+    db = ((16.0 * backdrop - 12.0) * backdrop + 4.0) * backdrop;
   else
     db = sqrt (backdrop);
 
   if (source <= 0.5)
-    return backdrop - (1 - 2 * source) * backdrop * (1 - backdrop);
+    return backdrop - (1.0 - 2.0 * source) * backdrop * (1.0 - backdrop);
   else
-    return backdrop + (2 * source - 1) * (db - backdrop);
+    return backdrop + (2.0 * source - 1.0) * (db - backdrop);
 }
 
 vec4
@@ -155,8 +155,8 @@ clip_color (vec3 c)
   float l = lum (c);
   float n = min (c.r, min (c.g, c.b));
   float x = max (c.r, max (c.g, c.b));
-  if (n < 0) c = l + (((c - l) * l) / (l - n));
-  if (x > 1) c = l + (((c - l) * (1 - l)) / (x - l));
+  if (n < 0.0) c = l + (((c - l) * l) / (l - n));
+  if (x > 1.0) c = l + (((c - l) * (1.0 - l)) / (x - l));
   return c;
 }
 
@@ -189,12 +189,12 @@ set_sat (vec3 c, float s)
           if (c.g == cmin)
             {
               res.b = ((c.b - cmin) * s) / (cmax - cmin);
-              res.g = 0;
+              res.g = 0.0;
             }
           else
             {
               res.g = ((c.g - cmin) * s) / (cmax - cmin);
-              res.b = 0;
+              res.b = 0.0;
             }
           res.r = s;
         }
@@ -203,12 +203,12 @@ set_sat (vec3 c, float s)
           if (c.r == cmin)
             {
               res.b = ((c.b - cmin) * s) / (cmax - cmin);
-              res.r = 0;
+              res.r = 0.0;
             }
           else
             {
               res.r = ((c.r - cmin) * s) / (cmax - cmin);
-              res.b = 0;
+              res.b = 0.0;
             }
           res.g = s;
         }
@@ -217,12 +217,12 @@ set_sat (vec3 c, float s)
           if (c.r == cmin)
             {
               res.g = ((c.g - cmin) * s) / (cmax - cmin);
-              res.r = 0;
+              res.r = 0.0;
             }
           else
             {
               res.r = ((c.r - cmin) * s) / (cmax - cmin);
-              res.g = 0;
+              res.g = 0.0;
             }
           res.b = s;
         }

gtk.supp

@@ -0,0 +1,213 @@
+# Actual GTK things
+{
+  GtkWidgetClass action GPtrArray
+  Memcheck:Leak
+  fun:malloc
+  fun:g_malloc
+  fun:g_slice_alloc
+  fun:g_ptr_array_sized_new
+  fun:g_ptr_array_new
+  fun:gtk_widget_class_add_action
+}
+
+{
+   GTK media extension gio modules
+   Memcheck:Leak
+   match-leak-kinds: definite
+   fun:malloc
+   fun:g_malloc
+   fun:g_slice_alloc
+   fun:g_slice_alloc0
+   fun:g_type_create_instance
+   fun:g_object_new_internal
+   fun:g_object_new_with_properties
+   fun:g_object_new
+   fun:g_io_module_new
+   fun:g_io_modules_scan_all_in_directory_with_scope
+   fun:gtk_media_file_extension_init
+}
+
+# mesa driver stuff
+{
+   i965 addr4
+   Memcheck:Addr4
+   obj:/usr/lib/dri/i965_dri.so*
+}
+
+{
+   i965 addr8
+   Memcheck:Addr8
+   obj:/usr/lib/dri/i965_dri.so*
+}
+
+{
+   i965 memcpy
+   Memcheck:Addr8
+   fun:memcpy*
+   obj:/usr/lib/dri/i965_dri.so*
+}
+
+{
+   i965 memcpy
+   Memcheck:Addr2
+   fun:memcpy*
+   obj:/usr/lib/dri/i965_dri.so*
+}
+
+{
+   mesa memcmp 8
+   Memcheck:Addr8
+   fun:*memcmp*
+   obj:/usr/lib/dri/i965_dri.so*
+}
+
+{
+   mesa memcmp 1
+   Memcheck:Addr1
+   fun:*memcmp*
+   obj:/usr/lib/dri/i965_dri.so*
+}
+
+{
+   mesa memset 8
+   Memcheck:Addr8
+   fun:*memset*
+   obj:/usr/lib/dri/i965_dri.so
+}
+
+{
+   mesa realpath
+   Memcheck:Leak
+   match-leak-kinds: definite
+   fun:malloc
+   fun:realpath@@GLIBC_2.3
+   obj:*
+   obj:*
+   obj:*
+   obj:*
+   obj:*
+   obj:*
+   obj:*
+   obj:*
+   fun:epoxy_eglInitialize_global_rewrite_ptr
+}
+
+{
+   mesa calloc
+   Memcheck:Leak
+   match-leak-kinds: definite
+   fun:calloc
+   obj:*
+   obj:*
+   obj:*
+   obj:*
+   obj:*
+   obj:*
+   obj:*
+   obj:*
+   obj:*
+   fun:epoxy_eglInitialize_global_rewrite_ptr
+}
+
+{
+   mesa malloc
+   Memcheck:Leak
+   match-leak-kinds: definite
+   fun:malloc
+   obj:/usr/lib/dri/i965_dri.so*
+}
+
+{
+   mesa glReadPixels
+   Memcheck:Addr16
+   obj:*
+   obj:*
+   obj:*
+   obj:*
+   obj:*
+   fun:epoxy_glReadPixels_global_rewrite_ptr
+}
+
+{
+   epoxy glxQueryServerString 1
+   Memcheck:Leak
+   fun:malloc
+   fun:XextAddDisplay
+   obj:*
+   obj:*
+   obj:*
+   obj:*
+   obj:*
+   fun:epoxy_glXQueryServerString_global_rewrite_ptr
+
+}
+
+{
+   epoxy glxQueryServerString 2
+   Memcheck:Leak
+   match-leak-kinds: definite
+   fun:malloc
+   fun:realpath*
+   obj:*
+   obj:*
+   obj:*
+   obj:*
+   obj:*
+   obj:*
+   obj:*
+   fun:epoxy_glXQueryServerString_global_rewrite_ptr
+}
+
+
+# Fontconfig
+{
+   FcFontSetList
+   Memcheck:Leak
+   match-leak-kinds: definite
+   fun:malloc
+   obj:/usr/lib/libfontconfig.so*
+   obj:/usr/lib/libfontconfig.so*
+   fun:FcFontSetList
+}
+
+{
+   FcFontRenderPrepare
+   Memcheck:Leak
+   match-leak-kinds: definite
+   fun:realloc
+   obj:/usr/lib/libfontconfig.so*
+   obj:/usr/lib/libfontconfig.so*
+   fun:FcFontRenderPrepare
+}
+
+{
+   FcDefaultSubstitute
+   Memcheck:Leak
+   match-leak-kinds: definite
+   fun:realloc
+   obj:/usr/lib/libfontconfig.so*
+   obj:/usr/lib/libfontconfig.so*
+   fun:FcDefaultSubstitute
+}
+
+# Pixman
+{
+   pixman_image_composite32
+   Memcheck:Cond
+   obj:/usr/lib/libpixman-1.so*
+   obj:/usr/lib/libpixman-1.so*
+   fun:pixman_image_composite32
+}
+
+# Pango
+{
+   pango 1
+   Memcheck:Leak
+   match-leak-kinds: definite
+   fun:realloc
+   obj:/usr/lib/libfontconfig.so*
+   obj:/usr/lib/libfontconfig.so*
+   obj:/usr/lib/libcairo.so*
+   fun:pango_cairo_fc_font_map_fontset_key_substitute
+}
+

gtk/gskpango.c

@@ -23,41 +23,26 @@
 #include "gsk/gskrendernodeprivate.h"
 #include "gskpango.h"
 #include "gtksnapshotprivate.h"
+#include "gtkstylecontextprivate.h"
+#include "gtktextlayoutprivate.h"
+#include "gtktextviewprivate.h"
 
 #include <math.h>
 
 #include <pango/pango.h>
 #include <cairo.h>
 
-#define GSK_PANGO_RENDERER_CLASS(klass)    (G_TYPE_CHECK_CLASS_CAST ((klass), GSK_TYPE_PANGO_RENDERER, GskPangoRendererClass))
-#define GSK_IS_PANGO_RENDERER_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), GSK_TYPE_PANGO_RENDERER))
-#define GSK_PANGO_RENDERER_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS ((obj), GSK_TYPE_PANGO_RENDERER, GskPangoRendererClass))
-
-/*
- * This is a PangoRenderer implementation that translates all the draw calls to
- * gsk render nodes, using the GtkSnapshot helper class. Glyphs are translated
- * to text nodes, all other draw calls fall back to cairo nodes.
- */
-
-struct _GskPangoRenderer
-{
-  PangoRenderer parent_instance;
-
-  GtkSnapshot *snapshot;
-  GdkRGBA fg_color;
-  graphene_rect_t bounds;
-
-  /* house-keeping options */
-  gboolean is_cached_renderer;
-};
-
-struct _GskPangoRendererClass
-{
-  PangoRendererClass parent_class;
-};
-
 G_DEFINE_TYPE (GskPangoRenderer, gsk_pango_renderer, PANGO_TYPE_RENDERER)
 
+void
+gsk_pango_renderer_set_state (GskPangoRenderer      *crenderer,
+                              GskPangoRendererState  state)
+{
+  g_return_if_fail (GSK_IS_PANGO_RENDERER (crenderer));
+
+  crenderer->state = state;
+}
+
 static void
 get_color (GskPangoRenderer *crenderer,
            PangoRenderPart   part,
@@ -158,15 +143,14 @@ gsk_pango_renderer_draw_rectangle (PangoRenderer     *renderer,
 {
   GskPangoRenderer *crenderer = (GskPangoRenderer *) (renderer);
   GdkRGBA rgba;
-  graphene_rect_t bounds;
 
   get_color (crenderer, part, &rgba);
-
-  graphene_rect_init (&bounds,
-                      (double)x / PANGO_SCALE, (double)y / PANGO_SCALE,
-                      (double)width / PANGO_SCALE, (double)height / PANGO_SCALE);
-
-  gtk_snapshot_append_color (crenderer->snapshot, &rgba, &bounds);
+  gtk_snapshot_append_color (crenderer->snapshot,
+                             &rgba,
+                             &GRAPHENE_RECT_INIT ((double)x / PANGO_SCALE,
+                                                  (double)y / PANGO_SCALE,
+                                                  (double)width / PANGO_SCALE,
+                                                  (double)height / PANGO_SCALE));
 }
 
 static void
@@ -336,6 +320,124 @@ gsk_pango_renderer_draw_shape (PangoRenderer  *renderer,
   cairo_destroy (cr);
 }
 
+static void
+text_renderer_set_rgba (GskPangoRenderer *crenderer,
+                        PangoRenderPart   part,
+                        const GdkRGBA    *rgba)
+{
+  PangoRenderer *renderer = PANGO_RENDERER (crenderer);
+  PangoColor color = { 0, };
+  guint16 alpha;
+
+  if (rgba)
+    {
+      color.red = (guint16)(rgba->red * 65535);
+      color.green = (guint16)(rgba->green * 65535);
+      color.blue = (guint16)(rgba->blue * 65535);
+      alpha = (guint16)(rgba->alpha * 65535);
+      pango_renderer_set_color (renderer, part, &color);
+      pango_renderer_set_alpha (renderer, part, alpha);
+    }
+  else
+    {
+      pango_renderer_set_color (renderer, part, NULL);
+      pango_renderer_set_alpha (renderer, part, 0);
+    }
+}
+
+static GtkTextAppearance *
+get_item_appearance (PangoItem *item)
+{
+  GSList *tmp_list = item->analysis.extra_attrs;
+
+  while (tmp_list)
+    {
+      PangoAttribute *attr = tmp_list->data;
+
+      if (attr->klass->type == gtk_text_attr_appearance_type)
+        return &((GtkTextAttrAppearance *)attr)->appearance;
+
+      tmp_list = tmp_list->next;
+    }
+
+  return NULL;
+}
+
+static void
+gsk_pango_renderer_prepare_run (PangoRenderer  *renderer,
+                                PangoLayoutRun *run)
+{
+  GtkStyleContext *context;
+  GskPangoRenderer *crenderer = GSK_PANGO_RENDERER (renderer);
+  GdkRGBA *bg_rgba = NULL;
+  GdkRGBA *fg_rgba = NULL;
+  GtkTextAppearance *appearance;
+
+  PANGO_RENDERER_CLASS (gsk_pango_renderer_parent_class)->prepare_run (renderer, run);
+
+  appearance = get_item_appearance (run->item);
+
+  if (appearance == NULL)
+    return;
+
+  context = gtk_widget_get_style_context (crenderer->widget);
+
+  if (appearance->draw_bg && crenderer->state == GSK_PANGO_RENDERER_NORMAL)
+    bg_rgba = appearance->bg_rgba;
+  else
+    bg_rgba = NULL;
+
+  text_renderer_set_rgba (crenderer, PANGO_RENDER_PART_BACKGROUND, bg_rgba);
+
+  if (crenderer->state == GSK_PANGO_RENDERER_SELECTED &&
+      GTK_IS_TEXT_VIEW (crenderer->widget))
+    {
+      GtkCssNode *selection_node;
+
+      selection_node = gtk_text_view_get_selection_node ((GtkTextView *)crenderer->widget);
+      gtk_style_context_save_to_node (context, selection_node);
+
+      gtk_style_context_get (context,
+                             "color", &fg_rgba,
+                             NULL);
+
+      gtk_style_context_restore (context);
+    }
+  else if (crenderer->state == GSK_PANGO_RENDERER_CURSOR && gtk_widget_has_focus (crenderer->widget))
+    {
+      gtk_style_context_get (context,
+                             "background-color", &fg_rgba,
+                             NULL);
+    }
+  else
+    fg_rgba = appearance->fg_rgba;
+
+  text_renderer_set_rgba (crenderer, PANGO_RENDER_PART_FOREGROUND, fg_rgba);
+
+  if (appearance->strikethrough_rgba)
+    text_renderer_set_rgba (crenderer, PANGO_RENDER_PART_STRIKETHROUGH, appearance->strikethrough_rgba);
+  else
+    text_renderer_set_rgba (crenderer, PANGO_RENDER_PART_STRIKETHROUGH, fg_rgba);
+
+  if (appearance->underline_rgba)
+    text_renderer_set_rgba (crenderer, PANGO_RENDER_PART_UNDERLINE, appearance->underline_rgba);
+  else if (appearance->underline == PANGO_UNDERLINE_ERROR)
+    {
+      if (!crenderer->error_color)
+        {
+          static const GdkRGBA red = { 1, 0, 0, 1 };
+          crenderer->error_color = gdk_rgba_copy (&red);
+        }
+
+      text_renderer_set_rgba (crenderer, PANGO_RENDER_PART_UNDERLINE, crenderer->error_color);
+    }
+  else
+    text_renderer_set_rgba (crenderer, PANGO_RENDER_PART_UNDERLINE, fg_rgba);
+
+  if (fg_rgba != appearance->fg_rgba)
+    gdk_rgba_free (fg_rgba);
+}
+
 static void
 gsk_pango_renderer_init (GskPangoRenderer *renderer G_GNUC_UNUSED)
 {
@@ -352,13 +454,14 @@ gsk_pango_renderer_class_init (GskPangoRendererClass *klass)
   renderer_class->draw_trapezoid = gsk_pango_renderer_draw_trapezoid;
   renderer_class->draw_error_underline = gsk_pango_renderer_draw_error_underline;
   renderer_class->draw_shape = gsk_pango_renderer_draw_shape;
+  renderer_class->prepare_run = gsk_pango_renderer_prepare_run;
 }
 
 static GskPangoRenderer *cached_renderer = NULL; /* MT-safe */
 G_LOCK_DEFINE_STATIC (cached_renderer);
 
-static GskPangoRenderer *
-acquire_renderer (void)
+GskPangoRenderer *
+gsk_pango_renderer_acquire (void)
 {
   GskPangoRenderer *renderer;
 
@@ -380,13 +483,20 @@ acquire_renderer (void)
   return renderer;
 }
 
-static void
-release_renderer (GskPangoRenderer *renderer)
+void
+gsk_pango_renderer_release (GskPangoRenderer *renderer)
 {
   if (G_LIKELY (renderer->is_cached_renderer))
     {
+      renderer->widget = NULL;
       renderer->snapshot = NULL;
 
+      if (renderer->error_color)
+        {
+          gdk_rgba_free (renderer->error_color);
+          renderer->error_color = NULL;
+        }
+
       G_UNLOCK (cached_renderer);
     }
   else
@@ -414,7 +524,7 @@ gtk_snapshot_append_layout (GtkSnapshot   *snapshot,
   g_return_if_fail (snapshot != NULL);
   g_return_if_fail (PANGO_IS_LAYOUT (layout));
 
-  crenderer = acquire_renderer ();
+  crenderer = gsk_pango_renderer_acquire ();
 
   crenderer->snapshot = snapshot;
   crenderer->fg_color = *color;
@@ -424,5 +534,5 @@ gtk_snapshot_append_layout (GtkSnapshot   *snapshot,
 
   pango_renderer_draw_layout (PANGO_RENDERER (crenderer), layout, 0, 0);
 
-  release_renderer (crenderer);
+  gsk_pango_renderer_release (crenderer);
 }

gtk/gskpango.h

@@ -24,15 +24,57 @@
 
 G_BEGIN_DECLS
 
-#define GSK_TYPE_PANGO_RENDERER (gsk_pango_renderer_get_type ())
+#define GSK_TYPE_PANGO_RENDERER            (gsk_pango_renderer_get_type ())
+#define GSK_PANGO_RENDERER(obj)            (G_TYPE_CHECK_INSTANCE_CAST ((obj), GSK_TYPE_PANGO_RENDERER, GskPangoRenderer))
+#define GSK_IS_PANGO_RENDERER(obj)         (G_TYPE_CHECK_INSTANCE_TYPE ((obj), GSK_TYPE_PANGO_RENDERER))
+#define GSK_PANGO_RENDERER_CLASS(klass)    (G_TYPE_CHECK_CLASS_CAST ((klass), GSK_TYPE_PANGO_RENDERER, GskPangoRendererClass))
+#define GSK_IS_PANGO_RENDERER_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), GSK_TYPE_PANGO_RENDERER))
+#define GSK_PANGO_RENDERER_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS ((obj), GSK_TYPE_PANGO_RENDERER, GskPangoRendererClass))
 
-#define GSK_PANGO_RENDERER(obj)               (G_TYPE_CHECK_INSTANCE_CAST ((obj), GSK_TYPE_PANGO_RENDERER, GskPangoRenderer))
-#define GSK_IS_PANGO_RENDERER(obj)            (G_TYPE_CHECK_INSTANCE_TYPE ((obj), GSK_TYPE_PANGO_RENDERER))
+typedef struct _GskPangoRenderer      GskPangoRenderer;
+typedef struct _GskPangoRendererClass GskPangoRendererClass;
 
-typedef struct _GskPangoRenderer        GskPangoRenderer;
-typedef struct _GskPangoRendererClass   GskPangoRendererClass;
+typedef enum
+{
+  GSK_PANGO_RENDERER_NORMAL,
+  GSK_PANGO_RENDERER_SELECTED,
+  GSK_PANGO_RENDERER_CURSOR
+} GskPangoRendererState;
 
-GType gsk_pango_renderer_get_type (void) G_GNUC_CONST;
+/*
+ * This is a PangoRenderer implementation that translates all the draw calls to
+ * gsk render nodes, using the GtkSnapshot helper class. Glyphs are translated
+ * to text nodes, all other draw calls fall back to cairo nodes.
+ */
+
+struct _GskPangoRenderer
+{
+  PangoRenderer          parent_instance;
+
+  GtkWidget             *widget;
+  GtkSnapshot           *snapshot;
+  GdkRGBA                fg_color;
+  graphene_rect_t        bounds;
+
+  /* Error underline color for this widget */
+  GdkRGBA               *error_color;
+
+  GskPangoRendererState  state;
+
+  /* house-keeping options */
+  guint                  is_cached_renderer : 1;
+};
+
+struct _GskPangoRendererClass
+{
+  PangoRendererClass parent_class;
+};
+
+GType             gsk_pango_renderer_get_type  (void) G_GNUC_CONST;
+void              gsk_pango_renderer_set_state (GskPangoRenderer      *crenderer,
+                                                GskPangoRendererState  state);
+GskPangoRenderer *gsk_pango_renderer_acquire   (void);
+void              gsk_pango_renderer_release   (GskPangoRenderer      *crenderer);
 
 G_END_DECLS
 

gtk/gtk.h

@@ -82,6 +82,8 @@
 #include <gtk/gtkcolorutils.h>
 #include <gtk/gtkcombobox.h>
 #include <gtk/gtkcomboboxtext.h>
+#include <gtk/gtkconstraintlayout.h>
+#include <gtk/gtkconstraint.h>
 #include <gtk/gtkcontainer.h>
 #include <gtk/gtkcssprovider.h>
 #include <gtk/gtkcustomlayout.h>

gtk/gtkaccelmap.c

@@ -155,6 +155,16 @@ accel_entry_equal (gconstpointer key1,
   return g_str_equal (entry1->accel_path, entry2->accel_path);
 }
 
+static int
+accel_entry_compare (gconstpointer a,
+                     gconstpointer b)
+{
+  const AccelEntry *entry1 = a;
+  const AccelEntry *entry2 = b;
+
+  return strcmp (entry1->accel_path, entry2->accel_path);
+}
+
 static inline AccelEntry*
 accel_path_lookup (const gchar *accel_path)
 {
@@ -817,17 +827,23 @@ gtk_accel_map_foreach (gpointer           data,
   g_return_if_fail (foreach_func != NULL);
 
   entries = g_hash_table_slist_values (accel_entry_ht);
+  entries = g_slist_sort (entries, accel_entry_compare);
+
   for (slist = entries; slist; slist = slist->next)
     {
       AccelEntry *entry = slist->data;
       gboolean changed = entry->accel_key != entry->std_accel_key || entry->accel_mods != entry->std_accel_mods;
+      gboolean skip = FALSE;
 
       for (node = accel_filters; node; node = node->next)
-	if (g_pattern_match_string (node->data, entry->accel_path))
-	  goto skip_accel;
-      foreach_func (data, entry->accel_path, entry->accel_key, entry->accel_mods, changed);
-    skip_accel:
-      /* noop */;
+        if (g_pattern_match_string (node->data, entry->accel_path))
+          {
+            skip = TRUE;
+            break;
+          }
+
+      if (!skip)
+        foreach_func (data, entry->accel_path, entry->accel_key, entry->accel_mods, changed);
     }
   g_slist_free (entries);
 }

gtk/gtkactionmuxer.c

@@ -561,13 +561,6 @@ prop_actions_connect (GtkActionMuxer *muxer)
     }
 }
 
-static void
-prop_actions_disconnect (GtkActionMuxer *muxer)
-{
-  if (muxer->widget)
-    g_signal_handlers_disconnect_by_func (muxer->widget,
-                                          prop_action_notify, muxer);
-}
 
 static gboolean
 gtk_action_muxer_query_action (GActionGroup        *action_group,
@@ -810,6 +803,8 @@ gtk_action_muxer_finalize (GObject *object)
   if (muxer->primary_accels)
     g_hash_table_unref (muxer->primary_accels);
 
+  g_free (muxer->widget_actions_enabled);
+
   G_OBJECT_CLASS (gtk_action_muxer_parent_class)
     ->finalize (object);
 }
@@ -819,8 +814,6 @@ gtk_action_muxer_dispose (GObject *object)
 {
   GtkActionMuxer *muxer = GTK_ACTION_MUXER (object);
 
-  prop_actions_disconnect (muxer);
-
   if (muxer->parent)
   {
     g_signal_handlers_disconnect_by_func (muxer->parent, gtk_action_muxer_action_added_to_parent, muxer);

gtk/gtkbuilder.c

@@ -289,7 +289,6 @@ gtk_builder_init (GtkBuilder *builder)
 {
   GtkBuilderPrivate *priv = gtk_builder_get_instance_private (builder);
 
-  priv = gtk_builder_get_instance_private (builder);
   priv->domain = NULL;
   priv->objects = g_hash_table_new_full (g_str_hash, g_str_equal,
                                          g_free, g_object_unref);

gtk/gtkcalendar.c

@@ -3474,7 +3474,7 @@ gtk_calendar_set_detail_width_chars (GtkCalendar *calendar,
     {
       priv->detail_width_chars = chars;
       g_object_notify (G_OBJECT (calendar), "detail-width-chars");
-      gtk_widget_queue_resize_no_redraw (GTK_WIDGET (calendar));
+      gtk_widget_queue_resize (GTK_WIDGET (calendar));
     }
 }
 
@@ -3498,7 +3498,7 @@ gtk_calendar_set_detail_height_rows (GtkCalendar *calendar,
     {
       priv->detail_height_rows = rows;
       g_object_notify (G_OBJECT (calendar), "detail-height-rows");
-      gtk_widget_queue_resize_no_redraw (GTK_WIDGET (calendar));
+      gtk_widget_queue_resize (GTK_WIDGET (calendar));
     }
 }
 

gtk/gtkcellrenderertext.c

@@ -1604,8 +1604,9 @@ get_size (GtkCellRenderer    *cell,
   GtkCellRendererText *celltext = GTK_CELL_RENDERER_TEXT (cell);
   GtkCellRendererTextPrivate *priv = gtk_cell_renderer_text_get_instance_private (celltext);
   PangoRectangle rect;
-  gint xpad, ypad;
-  gint cell_width, cell_height;
+  int xpad, ypad;
+  int cell_width, cell_height;
+  float xalign, yalign;
 
   gtk_cell_renderer_get_padding (cell, &xpad, &ypad);
 
@@ -1652,52 +1653,30 @@ get_size (GtkCellRenderer    *cell,
       if (width == NULL)
 	return;
     }
-  
-  if (layout)
-    g_object_ref (layout);
-  else
-    layout = get_layout (celltext, widget, NULL, 0);
 
   pango_layout_get_pixel_extents (layout, NULL, &rect);
 
-  if (cell_area)
-    {
-      gfloat xalign, yalign;
+  gtk_cell_renderer_get_alignment (cell, &xalign, &yalign);
 
-      gtk_cell_renderer_get_alignment (cell, &xalign, &yalign);
+  rect.height = MIN (rect.height, cell_area->height - 2 * ypad);
+  rect.width  = MIN (rect.width, cell_area->width - 2 * xpad);
 
-      rect.height = MIN (rect.height, cell_area->height - 2 * ypad);
-      rect.width  = MIN (rect.width, cell_area->width - 2 * xpad);
-
-      if (x_offset)
-	{
-	  if (gtk_widget_get_direction (widget) == GTK_TEXT_DIR_RTL)
-	    *x_offset = (1.0 - xalign) * (cell_area->width - (rect.width + (2 * xpad)));
-	  else 
-	    *x_offset = xalign * (cell_area->width - (rect.width + (2 * xpad)));
-
-	  if ((priv->ellipsize_set && priv->ellipsize != PANGO_ELLIPSIZE_NONE) || priv->wrap_width != -1)
-	    *x_offset = MAX(*x_offset, 0);
-	}
-      if (y_offset)
-	{
-	  *y_offset = yalign * (cell_area->height - (rect.height + (2 * ypad)));
-	  *y_offset = MAX (*y_offset, 0);
-	}
-    }
+  if (gtk_widget_get_direction (widget) == GTK_TEXT_DIR_RTL)
+    *x_offset = (1.0 - xalign) * (cell_area->width - (rect.width + (2 * xpad)));
   else
-    {
-      if (x_offset) *x_offset = 0;
-      if (y_offset) *y_offset = 0;
-    }
+    *x_offset = xalign * (cell_area->width - (rect.width + (2 * xpad)));
+
+  if ((priv->ellipsize_set && priv->ellipsize != PANGO_ELLIPSIZE_NONE) || priv->wrap_width != -1)
+    *x_offset = MAX(*x_offset, 0);
+
+  *y_offset = yalign * (cell_area->height - (rect.height + (2 * ypad)));
+  *y_offset = MAX (*y_offset, 0);
 
   if (height)
     *height = ypad * 2 + rect.height;
 
   if (width)
     *width = xpad * 2 + rect.width;
-
-  g_object_unref (layout);
 }
 
 static void

gtk/gtkcellrenderertoggle.c

@@ -408,7 +408,6 @@ gtk_cell_renderer_toggle_snapshot (GtkCellRenderer      *cell,
   GtkBorder padding, border;
   GtkCssImageBuiltinType image_type;
 
-  context = gtk_widget_get_style_context (widget);
   gtk_cell_renderer_toggle_get_size (cell, widget, cell_area,
 				     &x_offset, &y_offset,
 				     &width, &height);

gtk/gtkcolorchooserwidget.c

@@ -537,8 +537,6 @@ gtk_color_chooser_widget_init (GtkColorChooserWidget *cc)
   AtkObject *atk_obj;
   gchar *text, *name;
 
-  priv = gtk_color_chooser_widget_get_instance_private (cc);
-
   priv->use_alpha = TRUE;
 
   gtk_orientable_set_orientation (GTK_ORIENTABLE (cc), GTK_ORIENTATION_VERTICAL);

gtk/gtkconstraint.c

@@ -0,0 +1,614 @@
+/* gtkconstraint.c: Constraint between two widgets
+ * Copyright 2019  GNOME Foundation
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Author: Emmanuele Bassi
+ */
+
+/**
+ * SECTION:gtkconstraint
+ * @Title: GtkConstraint
+ * @Short_description: The description of a constraint
+ *
+ * #GtkConstraint describes a constraint between an attribute on a widget
+ * and another attribute on another widget, expressed as a linear equation
+ * like:
+ *
+ * |[
+ *   target.attr1 = source.attr2 × multiplier + constant
+ * ]|
+ *
+ * Each #GtkConstraint is part of a system that will be solved by a
+ * #GtkConstraintLayout in order to allocate and position each child widget.
+ *
+ * The source and target widgets, as well as their attributes, of a
+ * #GtkConstraint instance are immutable after creation.
+ */
+
+#include "config.h"
+
+#include "gtkconstraintprivate.h"
+#include "gtkconstraintsolverprivate.h"
+#include "gtkintl.h"
+#include "gtktypebuiltins.h"
+#include "gtkwidget.h"
+
+enum {
+  PROP_TARGET = 1,
+  PROP_TARGET_ATTRIBUTE,
+  PROP_RELATION,
+  PROP_SOURCE,
+  PROP_SOURCE_ATTRIBUTE,
+  PROP_MULTIPLIER,
+  PROP_CONSTANT,
+  PROP_STRENGTH,
+
+  N_PROPERTIES
+};
+
+static GParamSpec *obj_props[N_PROPERTIES];
+
+G_DEFINE_TYPE (GtkConstraint, gtk_constraint, G_TYPE_OBJECT)
+
+static void
+gtk_constraint_set_property (GObject      *gobject,
+                             guint         prop_id,
+                             const GValue *value,
+                             GParamSpec   *pspec)
+{
+  GtkConstraint *self = GTK_CONSTRAINT (gobject);
+
+  switch (prop_id)
+    {
+    case PROP_TARGET:
+      self->target = g_value_get_object (value);
+      break;
+
+    case PROP_TARGET_ATTRIBUTE:
+      self->target_attribute = g_value_get_enum (value);
+      break;
+
+    case PROP_RELATION:
+      self->relation = g_value_get_enum (value);
+      break;
+
+    case PROP_SOURCE:
+      self->source = g_value_get_object (value);
+      break;
+
+    case PROP_SOURCE_ATTRIBUTE:
+      self->source_attribute = g_value_get_enum (value);
+      break;
+
+    case PROP_MULTIPLIER:
+      self->multiplier = g_value_get_double (value);
+      break;
+
+    case PROP_CONSTANT:
+      self->constant = g_value_get_double (value);
+      break;
+
+    case PROP_STRENGTH:
+      self->strength = g_value_get_int (value);
+      break;
+
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (gobject, prop_id, pspec);
+      break;
+    }
+}
+
+static void
+gtk_constraint_get_property (GObject    *gobject,
+                             guint       prop_id,
+                             GValue     *value,
+                             GParamSpec *pspec)
+{
+  GtkConstraint *self = GTK_CONSTRAINT (gobject);
+
+  switch (prop_id)
+    {
+    case PROP_TARGET:
+      g_value_set_object (value, self->target);
+      break;
+
+    case PROP_TARGET_ATTRIBUTE:
+      g_value_set_enum (value, self->target_attribute);
+      break;
+
+    case PROP_RELATION:
+      g_value_set_enum (value, self->relation);
+      break;
+
+    case PROP_SOURCE:
+      g_value_set_object (value, self->source);
+      break;
+
+    case PROP_SOURCE_ATTRIBUTE:
+      g_value_set_enum (value, self->source_attribute);
+      break;
+
+    case PROP_MULTIPLIER:
+      g_value_set_double (value, self->multiplier);
+      break;
+
+    case PROP_CONSTANT:
+      g_value_set_double (value, self->constant);
+      break;
+
+    case PROP_STRENGTH:
+      g_value_set_int (value, self->strength);
+      break;
+
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (gobject, prop_id, pspec);
+      break;
+    }
+}
+
+static void
+gtk_constraint_finalize (GObject *gobject)
+{
+  GtkConstraint *self = GTK_CONSTRAINT (gobject);
+
+  gtk_constraint_detach (self);
+
+  G_OBJECT_CLASS (gtk_constraint_parent_class)->finalize (gobject);
+}
+
+static void
+gtk_constraint_class_init (GtkConstraintClass *klass)
+{
+  GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
+
+  gobject_class->set_property = gtk_constraint_set_property;
+  gobject_class->get_property = gtk_constraint_get_property;
+  gobject_class->finalize = gtk_constraint_finalize;
+
+  /**
+   * GtkConstraint:target:
+   *
+   * The target of the constraint.
+   *
+   * The constraint will set the #GtkConstraint:target-attribute of the
+   * target using the #GtkConstraint:source-attribute of the source
+   * widget.
+   */
+  obj_props[PROP_TARGET] =
+    g_param_spec_object ("target",
+                         P_("Target"),
+                         P_("The target of the constraint"),
+                         GTK_TYPE_CONSTRAINT_TARGET,
+                         G_PARAM_READWRITE |
+                         G_PARAM_STATIC_STRINGS |
+                         G_PARAM_CONSTRUCT_ONLY);
+  /**
+   * GtkConstraint:target-attribute:
+   *
+   * The attribute of the #GtkConstraint:target set by the constraint.
+   */
+  obj_props[PROP_TARGET_ATTRIBUTE] =
+    g_param_spec_enum ("target-attribute",
+                       P_("Target Attribute"),
+                       P_("The attribute of the target set by the constraint"),
+                       GTK_TYPE_CONSTRAINT_ATTRIBUTE,
+                       GTK_CONSTRAINT_ATTRIBUTE_NONE,
+                       G_PARAM_READWRITE |
+                       G_PARAM_STATIC_STRINGS |
+                       G_PARAM_CONSTRUCT_ONLY);
+  /**
+   * GtkConstraint:relation:
+   *
+   * The order relation between the terms of the constraint.
+   */
+  obj_props[PROP_RELATION] =
+    g_param_spec_enum ("relation",
+                       P_("Relation"),
+                       P_("The relation between the source and target attributes"),
+                       GTK_TYPE_CONSTRAINT_RELATION,
+                       GTK_CONSTRAINT_RELATION_EQ,
+                       G_PARAM_READWRITE |
+                       G_PARAM_STATIC_STRINGS |
+                       G_PARAM_CONSTRUCT_ONLY);
+  /**
+   * GtkConstraint:source:
+   *
+   * The source of the constraint.
+   *
+   * The constraint will set the #GtkConstraint:target-attribute of the
+   * target using the #GtkConstraint:source-attribute of the source.
+   */
+  obj_props[PROP_SOURCE] =
+    g_param_spec_object ("source",
+                         P_("Source"),
+                         P_("The source of the constraint"),
+                         GTK_TYPE_CONSTRAINT_TARGET,
+                         G_PARAM_READWRITE |
+                         G_PARAM_STATIC_STRINGS |
+                         G_PARAM_CONSTRUCT_ONLY);
+  /**
+   * GtkConstraint:source-attribute:
+   *
+   * The attribute of the #GtkConstraint:source read by the constraint.
+   */
+  obj_props[PROP_SOURCE_ATTRIBUTE] =
+    g_param_spec_enum ("source-attribute",
+                       P_("Source Attribute"),
+                       P_("The attribute of the source widget set by the constraint"),
+                       GTK_TYPE_CONSTRAINT_ATTRIBUTE,
+                       GTK_CONSTRAINT_ATTRIBUTE_NONE,
+                       G_PARAM_READWRITE |
+                       G_PARAM_STATIC_STRINGS |
+                       G_PARAM_CONSTRUCT_ONLY);
+  /**
+   * GtkConstraint:multiplier:
+   *
+   * The multiplication factor to be applied to the
+   * #GtkConstraint:source-attribute.
+   */
+  obj_props[PROP_MULTIPLIER] =
+    g_param_spec_double ("multiplier",
+                         P_("Multiplier"),
+                         P_("The multiplication factor to be applied to the source attribute"),
+                         -G_MAXDOUBLE, G_MAXDOUBLE, 1.0,
+                         G_PARAM_READWRITE |
+                         G_PARAM_STATIC_STRINGS |
+                         G_PARAM_CONSTRUCT_ONLY);
+  /**
+   * GtkConstraint:constant:
+   *
+   * The constant value to be added to the #GtkConstraint:source-attribute.
+   */
+  obj_props[PROP_CONSTANT] =
+    g_param_spec_double ("constant",
+                         P_("Constant"),
+                         P_("The constant to be added to the source attribute"),
+                         -G_MAXDOUBLE, G_MAXDOUBLE, 0.0,
+                         G_PARAM_READWRITE |
+                         G_PARAM_STATIC_STRINGS |
+                         G_PARAM_CONSTRUCT_ONLY);
+  /**
+   * GtkConstraint:strength:
+   *
+   * The strength of the constraint.
+   *
+   * The strength can be expressed either using one of the symbolic values
+   * of the #GtkConstraintStrength enumeration, or any positive integer
+   * value.
+   */
+  obj_props[PROP_STRENGTH] =
+    g_param_spec_int ("strength",
+                      P_("Strength"),
+                      P_("The strength of the constraint"),
+                      0, GTK_CONSTRAINT_STRENGTH_REQUIRED,
+                      GTK_CONSTRAINT_STRENGTH_REQUIRED,
+                      G_PARAM_READWRITE |
+                      G_PARAM_STATIC_STRINGS |
+                      G_PARAM_CONSTRUCT_ONLY);
+
+  g_object_class_install_properties (gobject_class, N_PROPERTIES, obj_props);
+}
+
+static void
+gtk_constraint_init (GtkConstraint *self)
+{
+  self->multiplier = 1.0;
+  self->constant = 0.0;
+
+  self->target_attribute = GTK_CONSTRAINT_ATTRIBUTE_NONE;
+  self->source_attribute = GTK_CONSTRAINT_ATTRIBUTE_NONE;
+  self->relation = GTK_CONSTRAINT_RELATION_EQ;
+  self->strength = GTK_CONSTRAINT_STRENGTH_REQUIRED;
+}
+
+/**
+ * gtk_constraint_new:
+ * @target: (nullable) (type GtkConstraintTarget): a #GtkConstraintTarget
+ * @target_attribute: the attribute of @target to be set
+ * @relation: the relation equivalence between @target_attribute and @source_attribute
+ * @source: (nullable) (type GtkConstraintTarget): a #GtkConstraintTarget
+ * @source_attribute: the attribute of @source to be read
+ * @multiplier: a multiplication factor to be applied to @source_attribute
+ * @constant: a constant factor to be added to @source_attribute
+ * @strength: the strength of the constraint
+ *
+ * Creates a new #GtkConstraint representing a relation between a layout
+ * attribute on a source and a layout attribute on a target.
+ *
+ * Returns: the newly created #GtkConstraint
+ */
+GtkConstraint *
+gtk_constraint_new (gpointer                target,
+                    GtkConstraintAttribute  target_attribute,
+                    GtkConstraintRelation   relation,
+                    gpointer                source,
+                    GtkConstraintAttribute  source_attribute,
+                    double                  multiplier,
+                    double                  constant,
+                    int                     strength)
+{
+  g_return_val_if_fail (target == NULL || GTK_IS_CONSTRAINT_TARGET (target), NULL);
+  g_return_val_if_fail (source == NULL || GTK_IS_CONSTRAINT_TARGET (source), NULL);
+
+  return g_object_new (GTK_TYPE_CONSTRAINT,
+                       "target", target,
+                       "target-attribute", target_attribute,
+                       "relation", relation,
+                       "source", source,
+                       "source-attribute", source_attribute,
+                       "multiplier", multiplier,
+                       "constant", constant,
+                       "strength", strength,
+                       NULL);
+}
+
+/**
+ * gtk_constraint_new_constant:
+ * @target: (nullable) (type GtkConstraintTarget): a #GtkConstraintTarget
+ * @target_attribute: the attribute of @target to be set
+ * @relation: the relation equivalence between @target_attribute and @constant
+ * @constant: a constant factor to be set on @target_attribute
+ * @strength: the strength of the constraint
+ *
+ * Creates a new #GtkConstraint representing a relation between a layout
+ * attribute on a target and a constant value.
+ *
+ * Returns: the newly created #GtkConstraint
+ */
+GtkConstraint *
+gtk_constraint_new_constant (gpointer                target,
+                             GtkConstraintAttribute  target_attribute,
+                             GtkConstraintRelation   relation,
+                             double                  constant,
+                             int                     strength)
+{
+  g_return_val_if_fail (target == NULL || GTK_IS_CONSTRAINT_TARGET (target), NULL);
+
+  return g_object_new (GTK_TYPE_CONSTRAINT,
+                       "target", target,
+                       "target-attribute", target_attribute,
+                       "relation", relation,
+                       "source-attribute", GTK_CONSTRAINT_ATTRIBUTE_NONE,
+                       "constant", constant,
+                       "strength", strength,
+                       NULL);
+}
+
+/**
+ * gtk_constraint_get_target:
+ * @constraint: a #GtkConstraint
+ *
+ * Retrieves the #GtkConstraintTarget used as the target for @constraint.
+ *
+ * If the #GtkConstraint:target property is set to %NULL, the @constraint
+ * will use the #GtkConstraintLayout's widget.
+ *
+ * Returns: (transfer none) (nullable): a #GtkConstraintTarget
+ */
+GtkConstraintTarget *
+gtk_constraint_get_target (GtkConstraint *constraint)
+{
+  g_return_val_if_fail (GTK_IS_CONSTRAINT (constraint), NULL);
+
+  return constraint->target;
+}
+
+/**
+ * gtk_constraint_get_target_attribute:
+ * @constraint: a #GtkConstraint
+ *
+ * Retrieves the attribute of the target to be set by the @constraint.
+ *
+ * Returns: the target's attribute
+ */
+GtkConstraintAttribute
+gtk_constraint_get_target_attribute (GtkConstraint *constraint)
+{
+  g_return_val_if_fail (GTK_IS_CONSTRAINT (constraint), GTK_CONSTRAINT_ATTRIBUTE_NONE);
+
+  return constraint->target_attribute;
+}
+
+/**
+ * gtk_constraint_get_source:
+ * @constraint: a #GtkConstraint
+ *
+ * Retrieves the #GtkConstraintTarget used as the source for @constraint.
+ *
+ * If the #GtkConstraint:source property is set to %NULL, the @constraint
+ * will use the #GtkConstraintLayout's widget.
+ *
+ * Returns: (transfer none) (nullable): a #GtkConstraintTarget
+ */
+GtkConstraintTarget *
+gtk_constraint_get_source (GtkConstraint *constraint)
+{
+  g_return_val_if_fail (GTK_IS_CONSTRAINT (constraint), NULL);
+
+  return constraint->source;
+}
+
+/**
+ * gtk_constraint_get_source_attribute:
+ * @constraint: a #GtkConstraint
+ *
+ * Retrieves the attribute of the source to be read by the @constraint.
+ *
+ * Returns: the target's attribute
+ */
+GtkConstraintAttribute
+gtk_constraint_get_source_attribute (GtkConstraint *constraint)
+{
+  g_return_val_if_fail (GTK_IS_CONSTRAINT (constraint), GTK_CONSTRAINT_ATTRIBUTE_NONE);
+
+  return constraint->source_attribute;
+}
+
+/**
+ * gtk_constraint_get_relation:
+ * @constraint: a #GtkConstraint
+ *
+ * The order relation between the terms of the @constraint.
+ *
+ * Returns: a #GtkConstraintRelation value
+ */
+GtkConstraintRelation
+gtk_constraint_get_relation (GtkConstraint *constraint)
+{
+  g_return_val_if_fail (GTK_IS_CONSTRAINT (constraint), GTK_CONSTRAINT_RELATION_EQ);
+
+  return constraint->relation;
+}
+
+/**
+ * gtk_constraint_get_multiplier:
+ * @constraint: a #GtkConstraint
+ *
+ * Retrieves the multiplication factor applied to the source
+ * attribute's value.
+ *
+ * Returns: a multiplication factor
+ */
+double
+gtk_constraint_get_multiplier (GtkConstraint *constraint)
+{
+  g_return_val_if_fail (GTK_IS_CONSTRAINT (constraint), 1.0);
+
+  return constraint->multiplier;
+}
+
+/**
+ * gtk_constraint_get_constant:
+ * @constraint: a #GtkConstraint
+ *
+ * Retrieves the constant factor added to the source attributes' value.
+ *
+ * Returns: a constant factor
+ */
+double
+gtk_constraint_get_constant (GtkConstraint *constraint)
+{
+  g_return_val_if_fail (GTK_IS_CONSTRAINT (constraint), 0.0);
+
+  return constraint->constant;
+}
+
+/**
+ * gtk_constraint_get_strength:
+ * @constraint: a #GtkConstraint
+ *
+ * Retrieves the strength of the constraint.
+ *
+ * Returns: the strength of the constraint
+ */
+int
+gtk_constraint_get_strength (GtkConstraint *constraint)
+{
+  g_return_val_if_fail (GTK_IS_CONSTRAINT (constraint), GTK_CONSTRAINT_STRENGTH_REQUIRED);
+
+  return constraint->strength;
+}
+
+/**
+ * gtk_constraint_is_required:
+ * @constraint: a #GtkConstraint
+ *
+ * Checks whether the @constraint is a required relation for solving the
+ * constraint layout.
+ *
+ * Returns: %TRUE if the constraint is required
+ */
+gboolean
+gtk_constraint_is_required (GtkConstraint *constraint)
+{
+  g_return_val_if_fail (GTK_IS_CONSTRAINT (constraint), FALSE);
+
+  return constraint->strength == GTK_CONSTRAINT_STRENGTH_REQUIRED;
+}
+
+/**
+ * gtk_constraint_is_attached:
+ * @constraint: a #GtkConstraint
+ *
+ * Checks whether the @constraint is attached to a #GtkConstraintLayout,
+ * and it is contributing to the layout.
+ *
+ * Returns: %TRUE if the constraint is attached
+ */
+gboolean
+gtk_constraint_is_attached (GtkConstraint *constraint)
+{
+  g_return_val_if_fail (GTK_IS_CONSTRAINT (constraint), FALSE);
+
+  return constraint->constraint_ref != NULL;
+}
+
+/**
+ * gtk_constraint_is_constant:
+ * @constraint: a #GtkConstraint
+ *
+ * Checks whether the @constraint describes a relation between an attribute
+ * on the #GtkConstraint:target-widget and a constant value.
+ *
+ * Returns: %TRUE if the constraint is a constant relation
+ */
+gboolean
+gtk_constraint_is_constant (GtkConstraint *constraint)
+{
+  g_return_val_if_fail (GTK_IS_CONSTRAINT (constraint), FALSE);
+
+  return constraint->source == NULL &&
+         constraint->source_attribute == GTK_CONSTRAINT_ATTRIBUTE_NONE;
+}
+
+void
+gtk_constraint_attach (GtkConstraint       *constraint,
+                       GtkConstraintSolver *solver,
+                       GtkConstraintRef    *ref)
+{
+  g_return_if_fail (GTK_IS_CONSTRAINT (constraint));
+  g_return_if_fail (GTK_IS_CONSTRAINT_SOLVER (solver));
+  g_return_if_fail (ref != NULL);
+
+  constraint->constraint_ref = ref;
+  constraint->solver = solver;
+}
+
+void
+gtk_constraint_detach (GtkConstraint *constraint)
+{
+  g_return_if_fail (GTK_IS_CONSTRAINT (constraint));
+
+  if (constraint->constraint_ref == NULL)
+    return;
+
+  gtk_constraint_solver_remove_constraint (constraint->solver, constraint->constraint_ref);
+  constraint->constraint_ref = NULL;
+  constraint->solver = NULL;
+}
+
+typedef struct _GtkConstraintTargetInterface GtkConstraintTargetInterface;
+
+struct _GtkConstraintTargetInterface
+{
+  GTypeInterface g_iface;
+};
+
+G_DEFINE_INTERFACE (GtkConstraintTarget, gtk_constraint_target, G_TYPE_OBJECT)
+
+static void
+gtk_constraint_target_default_init (GtkConstraintTargetInterface *iface)
+{
+}

gtk/gtkconstraint.h

@@ -0,0 +1,100 @@
+/* gtkconstraint.h: Constraint between two widgets
+ * Copyright 2019  GNOME Foundation
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Author: Emmanuele Bassi
+ */
+
+#pragma once
+
+#include <gtk/gtktypes.h>
+#include <gtk/gtkenums.h>
+
+G_BEGIN_DECLS
+
+typedef struct _GtkConstraintTarget GtkConstraintTarget;
+
+#define GTK_TYPE_CONSTRAINT_TARGET (gtk_constraint_target_get_type ())
+
+/**
+ * GtkConstraintTarget:
+ *
+ * The GtkConstraintTarget interface is implemented by objects that
+ * can be used as source or target in #GtkConstraints. Besides
+ * #GtkWidget, it is also implemented by #GtkConstraintGuide.
+ */
+
+GDK_AVAILABLE_IN_ALL
+G_DECLARE_INTERFACE (GtkConstraintTarget, gtk_constraint_target, GTK, CONSTRAINT_TARGET, GObject)
+
+#define GTK_TYPE_CONSTRAINT (gtk_constraint_get_type ())
+
+/**
+ * GtkConstraint:
+ *
+ * An object describing the relation between two widget attributes.
+ *
+ * All relations are in the form:
+ *
+ * |[<!-- language=plain -->
+ *   target.attr_name = source.attr_name × multiplier + constant
+ * ]|
+ *
+ * A #GtkConstraint is immutable once it's created.
+ */
+GDK_AVAILABLE_IN_ALL
+G_DECLARE_FINAL_TYPE (GtkConstraint, gtk_constraint, GTK, CONSTRAINT, GObject)
+
+GDK_AVAILABLE_IN_ALL
+GtkConstraint *         gtk_constraint_new                      (gpointer                target,
+                                                                 GtkConstraintAttribute  target_attribute,
+                                                                 GtkConstraintRelation   relation,
+                                                                 gpointer                source,
+                                                                 GtkConstraintAttribute  source_attribute,
+                                                                 double                  multiplier,
+                                                                 double                  constant,
+                                                                 int                     strength);
+GDK_AVAILABLE_IN_ALL
+GtkConstraint *         gtk_constraint_new_constant             (gpointer                target,
+                                                                 GtkConstraintAttribute  target_attribute,
+                                                                 GtkConstraintRelation   relation,
+                                                                 double                  constant,
+                                                                 int                     strength);
+
+GDK_AVAILABLE_IN_ALL
+GtkConstraintTarget *   gtk_constraint_get_target               (GtkConstraint          *constraint);
+GDK_AVAILABLE_IN_ALL
+GtkConstraintAttribute  gtk_constraint_get_target_attribute     (GtkConstraint          *constraint);
+GDK_AVAILABLE_IN_ALL
+GtkConstraintTarget *   gtk_constraint_get_source               (GtkConstraint          *constraint);
+GDK_AVAILABLE_IN_ALL
+GtkConstraintAttribute  gtk_constraint_get_source_attribute     (GtkConstraint          *constraint);
+GDK_AVAILABLE_IN_ALL
+GtkConstraintRelation   gtk_constraint_get_relation             (GtkConstraint          *constraint);
+GDK_AVAILABLE_IN_ALL
+double                  gtk_constraint_get_multiplier           (GtkConstraint          *constraint);
+GDK_AVAILABLE_IN_ALL
+double                  gtk_constraint_get_constant             (GtkConstraint          *constraint);
+GDK_AVAILABLE_IN_ALL
+int                     gtk_constraint_get_strength             (GtkConstraint          *constraint);
+
+GDK_AVAILABLE_IN_ALL
+gboolean                gtk_constraint_is_required              (GtkConstraint          *constraint);
+GDK_AVAILABLE_IN_ALL
+gboolean                gtk_constraint_is_attached              (GtkConstraint          *constraint);
+GDK_AVAILABLE_IN_ALL
+gboolean                gtk_constraint_is_constant              (GtkConstraint          *constraint);
+
+G_END_DECLS

gtk/gtkconstraintexpressionprivate.h

@@ -0,0 +1,279 @@
+/* gtkconstraintequationprivate.h: Constraint expressions and variables
+ * Copyright 2019  GNOME Foundation
+ *
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Author: Emmanuele Bassi
+ */
+
+#pragma once
+
+#include "gtkconstrainttypesprivate.h"
+
+G_BEGIN_DECLS
+
+GtkConstraintVariable *
+gtk_constraint_variable_new (const char *prefix,
+                             const char *name);
+
+GtkConstraintVariable *
+gtk_constraint_variable_new_dummy (const char *name);
+
+GtkConstraintVariable *
+gtk_constraint_variable_new_objective (const char *name);
+
+GtkConstraintVariable *
+gtk_constraint_variable_new_slack (const char *name);
+
+GtkConstraintVariable *
+gtk_constraint_variable_ref (GtkConstraintVariable *variable);
+
+void
+gtk_constraint_variable_unref (GtkConstraintVariable *variable);
+
+void
+gtk_constraint_variable_set_value (GtkConstraintVariable *variable,
+                                   double value);
+
+double
+gtk_constraint_variable_get_value (const GtkConstraintVariable *variable);
+
+char *
+gtk_constraint_variable_to_string (const GtkConstraintVariable *variable);
+
+gboolean
+gtk_constraint_variable_is_external (const GtkConstraintVariable *variable);
+
+gboolean
+gtk_constraint_variable_is_pivotable (const GtkConstraintVariable *variable);
+
+gboolean
+gtk_constraint_variable_is_restricted (const GtkConstraintVariable *variable);
+
+gboolean
+gtk_constraint_variable_is_dummy (const GtkConstraintVariable *variable);
+
+typedef struct {
+  GtkConstraintVariable *first;
+  GtkConstraintVariable *second;
+} GtkConstraintVariablePair;
+
+GtkConstraintVariablePair *
+gtk_constraint_variable_pair_new (GtkConstraintVariable *first,
+                                  GtkConstraintVariable *second);
+
+void
+gtk_constraint_variable_pair_free (GtkConstraintVariablePair *pair);
+
+typedef struct _GtkConstraintVariableSet        GtkConstraintVariableSet;
+
+GtkConstraintVariableSet *
+gtk_constraint_variable_set_new (void);
+
+void
+gtk_constraint_variable_set_free (GtkConstraintVariableSet *set);
+
+gboolean
+gtk_constraint_variable_set_add (GtkConstraintVariableSet *set,
+                                 GtkConstraintVariable *variable);
+
+gboolean
+gtk_constraint_variable_set_remove (GtkConstraintVariableSet *set,
+                                    GtkConstraintVariable *variable);
+
+gboolean
+gtk_constraint_variable_set_is_empty (GtkConstraintVariableSet *set);
+
+gboolean
+gtk_constraint_variable_set_is_singleton (GtkConstraintVariableSet *set);
+
+int
+gtk_constraint_variable_set_size (GtkConstraintVariableSet *set);
+
+typedef struct {
+  /*< private >*/
+  gpointer dummy1;
+  gpointer dummy2;
+  gint64 dummy3;
+} GtkConstraintVariableSetIter;
+
+void
+gtk_constraint_variable_set_iter_init (GtkConstraintVariableSetIter *iter,
+                                       GtkConstraintVariableSet *set);
+
+gboolean
+gtk_constraint_variable_set_iter_next (GtkConstraintVariableSetIter *iter,
+                                       GtkConstraintVariable **variable_p);
+
+GtkConstraintExpression *
+gtk_constraint_expression_new (double constant);
+
+GtkConstraintExpression *
+gtk_constraint_expression_new_from_variable (GtkConstraintVariable *variable);
+
+GtkConstraintExpression *
+gtk_constraint_expression_ref (GtkConstraintExpression *expression);
+
+void
+gtk_constraint_expression_unref (GtkConstraintExpression *expression);
+
+GtkConstraintExpression *
+gtk_constraint_expression_clone (GtkConstraintExpression *expression);
+
+void
+gtk_constraint_expression_set_constant (GtkConstraintExpression *expression,
+                                        double constant);
+double
+gtk_constraint_expression_get_constant (const GtkConstraintExpression *expression);
+
+gboolean
+gtk_constraint_expression_is_constant (const GtkConstraintExpression *expression);
+
+void
+gtk_constraint_expression_add_expression (GtkConstraintExpression *a_expr,
+                                          GtkConstraintExpression *b_expr,
+                                          double n,
+                                          GtkConstraintVariable *subject,
+                                          GtkConstraintSolver *solver);
+
+void
+gtk_constraint_expression_add_variable (GtkConstraintExpression *expression,
+                                        GtkConstraintVariable *variable,
+                                        double coefficient,
+                                        GtkConstraintVariable *subject,
+                                        GtkConstraintSolver *solver);
+
+void
+gtk_constraint_expression_remove_variable (GtkConstraintExpression *expression,
+                                           GtkConstraintVariable *variable);
+
+void
+gtk_constraint_expression_set_variable (GtkConstraintExpression *expression,
+                                        GtkConstraintVariable *variable,
+                                        double coefficient);
+
+double
+gtk_constraint_expression_get_coefficient (GtkConstraintExpression *expression,
+                                           GtkConstraintVariable *variable);
+
+char *
+gtk_constraint_expression_to_string (const GtkConstraintExpression *expression);
+
+double
+gtk_constraint_expression_new_subject (GtkConstraintExpression *expression,
+                                       GtkConstraintVariable *subject);
+
+void
+gtk_constraint_expression_change_subject (GtkConstraintExpression *expression,
+                                          GtkConstraintVariable *old_subject,
+                                          GtkConstraintVariable *new_subject);
+
+void
+gtk_constraint_expression_substitute_out (GtkConstraintExpression *expression,
+                                          GtkConstraintVariable *out_var,
+                                          GtkConstraintExpression *expr,
+                                          GtkConstraintVariable *subject,
+                                          GtkConstraintSolver *solver);
+
+GtkConstraintVariable *
+gtk_constraint_expression_get_pivotable_variable (GtkConstraintExpression *expression);
+
+GtkConstraintExpression *
+gtk_constraint_expression_plus_constant (GtkConstraintExpression *expression,
+                                         double constant);
+
+GtkConstraintExpression *
+gtk_constraint_expression_minus_constant (GtkConstraintExpression *expression,
+                                          double constant);
+
+GtkConstraintExpression *
+gtk_constraint_expression_plus_variable (GtkConstraintExpression *expression,
+                                         GtkConstraintVariable *variable);
+
+GtkConstraintExpression *
+gtk_constraint_expression_minus_variable (GtkConstraintExpression *expression,
+                                          GtkConstraintVariable *variable);
+
+GtkConstraintExpression *
+gtk_constraint_expression_multiply_by (GtkConstraintExpression *expression,
+                                       double factor);
+
+GtkConstraintExpression *
+gtk_constraint_expression_divide_by (GtkConstraintExpression *expression,
+                                     double factor);
+
+struct _GtkConstraintExpressionBuilder
+{
+  /*< private >*/
+  gpointer dummy1;
+  gpointer dummy2;
+  int dummy3;
+};
+
+void
+gtk_constraint_expression_builder_init (GtkConstraintExpressionBuilder *builder,
+                                        GtkConstraintSolver *solver);
+
+void
+gtk_constraint_expression_builder_term (GtkConstraintExpressionBuilder *builder,
+                                        GtkConstraintVariable *term);
+
+void
+gtk_constraint_expression_builder_plus (GtkConstraintExpressionBuilder *builder);
+
+void
+gtk_constraint_expression_builder_minus (GtkConstraintExpressionBuilder *builder);
+
+void
+gtk_constraint_expression_builder_divide_by (GtkConstraintExpressionBuilder *builder);
+
+void
+gtk_constraint_expression_builder_multiply_by (GtkConstraintExpressionBuilder *builder);
+
+void
+gtk_constraint_expression_builder_constant (GtkConstraintExpressionBuilder *builder,
+                                            double value);
+
+GtkConstraintExpression *
+gtk_constraint_expression_builder_finish (GtkConstraintExpressionBuilder *builder) G_GNUC_WARN_UNUSED_RESULT;
+
+/*< private >
+ * GtkConstraintExpressionIter:
+ *
+ * An iterator object for terms inside a #GtkConstraintExpression.
+ */
+typedef struct {
+  /*< private >*/
+  gpointer dummy1;
+  gpointer dummy2;
+  gint64 dummy3;
+} GtkConstraintExpressionIter;
+
+void
+gtk_constraint_expression_iter_init (GtkConstraintExpressionIter *iter,
+                                     GtkConstraintExpression *equation);
+
+gboolean
+gtk_constraint_expression_iter_next (GtkConstraintExpressionIter *iter,
+                                     GtkConstraintVariable **variable,
+                                     double *coefficient);
+
+gboolean
+gtk_constraint_expression_iter_prev (GtkConstraintExpressionIter *iter,
+                                     GtkConstraintVariable **variable,
+                                     double *coefficient);
+
+G_END_DECLS

gtk/gtkconstraintguide.c

@@ -0,0 +1,694 @@
+/* gtkconstraintguide.c: Flexible space for constraints
+ * Copyright 2019 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Author: Matthias Clasen
+ */
+
+/**
+ * SECTION:gtkconstraintguide
+ * @Title: GtkConstraintGuide
+ * @Short_description: An invisible constraint target
+ *
+ * A #GtkConstraintGuide is an invisible layout element that can be
+ * used by widgets inside a #GtkConstraintLayout as a source or a target
+ * of a #GtkConstraint. Guides can be used like guidelines or as
+ * flexible space.
+ *
+ * Unlike a #GtkWidget, a #GtkConstraintGuide will not be drawn.
+ */
+
+#include "config.h"
+
+#include "gtkconstraintguide.h"
+
+#include "gtkconstraintguideprivate.h"
+#include "gtkconstraintlayoutprivate.h"
+#include "gtkconstraintexpressionprivate.h"
+#include "gtkconstraintsolverprivate.h"
+
+#include "gtkdebug.h"
+#include "gtkintl.h"
+#include "gtkprivate.h"
+
+
+typedef enum {
+  MIN_WIDTH,
+  MIN_HEIGHT,
+  NAT_WIDTH,
+  NAT_HEIGHT,
+  MAX_WIDTH,
+  MAX_HEIGHT,
+  LAST_VALUE
+} GuideValue;
+
+struct _GtkConstraintGuide
+{ 
+  GObject parent_instance;
+
+  char *name;
+
+  int strength;
+
+  int values[LAST_VALUE];
+
+  GtkConstraintLayout *layout;
+
+  /* HashTable<static string, Variable>; a hash table of variables,
+   * one for each attribute; we use these to query and suggest the
+   * values for the solver. The string is static and does not need
+   * to be freed.
+   */
+  GHashTable *bound_attributes;
+
+  GtkConstraintRef *constraints[LAST_VALUE];
+};
+
+
+struct _GtkConstraintGuideClass {
+  GObjectClass parent_class;
+};
+
+enum {
+  PROP_MIN_WIDTH = 1,
+  PROP_MIN_HEIGHT,
+  PROP_NAT_WIDTH,
+  PROP_NAT_HEIGHT,
+  PROP_MAX_WIDTH,
+  PROP_MAX_HEIGHT,
+  PROP_STRENGTH,
+  PROP_NAME,
+  LAST_PROP
+};
+
+static GParamSpec *guide_props[LAST_PROP];
+
+static void
+gtk_constraint_guide_constraint_target_iface_init (GtkConstraintTargetInterface *iface)
+{
+}
+
+G_DEFINE_TYPE_WITH_CODE (GtkConstraintGuide, gtk_constraint_guide, G_TYPE_OBJECT,
+                         G_IMPLEMENT_INTERFACE (GTK_TYPE_CONSTRAINT_TARGET,
+                                                gtk_constraint_guide_constraint_target_iface_init))
+
+static void
+gtk_constraint_guide_init (GtkConstraintGuide *guide)
+{
+  guide->strength = GTK_CONSTRAINT_STRENGTH_MEDIUM;
+
+  guide->values[MIN_WIDTH] = 0;
+  guide->values[MIN_HEIGHT] = 0;
+  guide->values[NAT_WIDTH] = 0;
+  guide->values[NAT_HEIGHT] = 0;
+  guide->values[MAX_WIDTH] = G_MAXINT;
+  guide->values[MAX_HEIGHT] = G_MAXINT;
+
+  guide->bound_attributes =
+    g_hash_table_new_full (g_str_hash, g_str_equal,
+                           NULL,
+                           (GDestroyNotify) gtk_constraint_variable_unref);
+}
+
+static void
+gtk_constraint_guide_update_constraint (GtkConstraintGuide *guide,
+                                        GuideValue          index)
+{
+  GtkConstraintSolver *solver;
+  GtkConstraintVariable *var;
+
+  if (!guide->layout)
+    return;
+
+  solver = gtk_constraint_layout_get_solver (guide->layout);
+  if (!solver)
+    return;
+
+  if (guide->constraints[index] != NULL)
+    {
+      gtk_constraint_solver_remove_constraint (solver, guide->constraints[index]);
+      guide->constraints[index] = NULL;
+    }
+
+  if (index == MIN_WIDTH || index == NAT_WIDTH || index == MAX_WIDTH)
+    var = gtk_constraint_layout_get_attribute (guide->layout, GTK_CONSTRAINT_ATTRIBUTE_WIDTH, "guide", NULL, guide->bound_attributes);
+  else
+    var = gtk_constraint_layout_get_attribute (guide->layout, GTK_CONSTRAINT_ATTRIBUTE_HEIGHT, "guide", NULL, guide->bound_attributes);
+
+  /* We always install min-size constraints,
+   * but we avoid nat-size constraints if min == max
+   * and we avoid max-size constraints if max == G_MAXINT
+   */
+  if (index == MIN_WIDTH || index == MIN_HEIGHT)
+    {
+      guide->constraints[index] =
+        gtk_constraint_solver_add_constraint (solver,
+                                              var,
+                                              GTK_CONSTRAINT_RELATION_GE,
+                                              gtk_constraint_expression_new (guide->values[index]),
+                                              GTK_CONSTRAINT_STRENGTH_REQUIRED);
+    }
+  else if ((index == NAT_WIDTH && guide->values[MIN_WIDTH] != guide->values[MAX_WIDTH]) ||
+      (index == NAT_HEIGHT && guide->values[MIN_HEIGHT] != guide->values[MAX_HEIGHT]))
+    {
+      gtk_constraint_variable_set_value (var, guide->values[index]);
+      guide->constraints[index] =
+        gtk_constraint_solver_add_stay_variable (solver,
+                                                 var,
+                                                 guide->strength);
+    }
+  else if ((index == MAX_WIDTH || index == MAX_HEIGHT) &&
+           guide->values[index] < G_MAXINT)
+    {
+      guide->constraints[index] =
+        gtk_constraint_solver_add_constraint (solver,
+                                              var,
+                                              GTK_CONSTRAINT_RELATION_LE,
+                                              gtk_constraint_expression_new (guide->values[index]),
+                                              GTK_CONSTRAINT_STRENGTH_REQUIRED);
+    }
+
+  gtk_layout_manager_layout_changed (GTK_LAYOUT_MANAGER (guide->layout));
+}
+
+void
+gtk_constraint_guide_update (GtkConstraintGuide *guide)
+{
+  int i;
+
+  for (i = 0; i < LAST_VALUE; i++)
+    gtk_constraint_guide_update_constraint (guide, i);
+}
+
+void
+gtk_constraint_guide_detach (GtkConstraintGuide *guide)
+{
+  GtkConstraintSolver *solver;
+  int i;
+
+  if (!guide->layout)
+    return;
+
+  solver = gtk_constraint_layout_get_solver (guide->layout);
+  if (!solver)
+    return;
+
+  for (i = 0; i < LAST_VALUE; i++)
+    {
+      if (guide->constraints[i])
+        {
+          gtk_constraint_solver_remove_constraint (solver, guide->constraints[i]);
+          guide->constraints[i] = NULL;
+        }
+    }
+
+  g_hash_table_remove_all (guide->bound_attributes);
+}
+
+GtkConstraintVariable *
+gtk_constraint_guide_get_attribute (GtkConstraintGuide     *guide,
+                                    GtkConstraintAttribute  attr)
+{
+  GtkLayoutManager *manager = GTK_LAYOUT_MANAGER (guide->layout);
+  GtkWidget *widget = gtk_layout_manager_get_widget (manager);
+
+  return gtk_constraint_layout_get_attribute (guide->layout, attr, "guide", widget, guide->bound_attributes);
+}
+
+GtkConstraintLayout *
+gtk_constraint_guide_get_layout (GtkConstraintGuide *guide)
+{
+  return guide->layout;
+}
+
+void
+gtk_constraint_guide_set_layout (GtkConstraintGuide  *guide,
+                                 GtkConstraintLayout *layout)
+{
+  guide->layout = layout;
+}
+
+static void
+gtk_constraint_guide_set_property (GObject      *gobject,
+                                   guint         prop_id,
+                                   const GValue *value,
+                                   GParamSpec   *pspec)
+{
+  GtkConstraintGuide *self = GTK_CONSTRAINT_GUIDE (gobject);
+  int val;
+  GuideValue index;
+
+  switch (prop_id)
+    {
+    case PROP_MIN_WIDTH:
+    case PROP_MIN_HEIGHT:
+    case PROP_NAT_WIDTH:
+    case PROP_NAT_HEIGHT:
+    case PROP_MAX_WIDTH:
+    case PROP_MAX_HEIGHT:
+      val = g_value_get_int (value);
+      index = prop_id - 1;
+      if (self->values[index] != val)
+        {
+          self->values[index] = val;
+          g_object_notify_by_pspec (gobject, pspec);
+
+          gtk_constraint_guide_update_constraint (self, index);
+          if (index == MIN_WIDTH || index == MAX_WIDTH)
+            gtk_constraint_guide_update_constraint (self, NAT_WIDTH);
+          if (index == MIN_HEIGHT || index == MAX_HEIGHT)
+            gtk_constraint_guide_update_constraint (self, NAT_HEIGHT);
+        }
+      break;
+
+    case PROP_STRENGTH:
+      gtk_constraint_guide_set_strength (self, g_value_get_enum (value));
+      break;
+
+    case PROP_NAME:
+      gtk_constraint_guide_set_name (self, g_value_get_string (value));
+      break;
+
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (gobject, prop_id, pspec);
+      break;
+    }
+}
+
+static void
+gtk_constraint_guide_get_property (GObject    *gobject,
+                                   guint       prop_id,
+                                   GValue     *value,
+                                   GParamSpec *pspec)
+{
+  GtkConstraintGuide *self = GTK_CONSTRAINT_GUIDE (gobject);
+
+  switch (prop_id)
+    {
+    case PROP_MIN_WIDTH:
+    case PROP_MIN_HEIGHT:
+    case PROP_NAT_WIDTH:
+    case PROP_NAT_HEIGHT:
+    case PROP_MAX_WIDTH:
+    case PROP_MAX_HEIGHT:
+      g_value_set_int (value, self->values[prop_id - 1]);
+      break;
+
+    case PROP_STRENGTH:
+      g_value_set_enum (value, self->strength);
+      break;
+
+    case PROP_NAME:
+      g_value_set_string (value, self->name);
+      break;
+
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (gobject, prop_id, pspec);
+      break;
+    }
+}
+
+static void
+gtk_constraint_guide_finalize (GObject *object)
+{
+  GtkConstraintGuide *self = GTK_CONSTRAINT_GUIDE (object);
+
+  g_free (self->name);
+
+  g_clear_pointer (&self->bound_attributes, g_hash_table_unref);
+
+  G_OBJECT_CLASS (gtk_constraint_guide_parent_class)->finalize (object);
+}
+
+static void
+gtk_constraint_guide_class_init (GtkConstraintGuideClass *class)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (class);
+
+  object_class->finalize = gtk_constraint_guide_finalize;
+  object_class->set_property = gtk_constraint_guide_set_property;
+  object_class->get_property = gtk_constraint_guide_get_property;
+
+  /**
+   * GtkConstraintGuide:min-width:
+   *
+   * The minimum width of the guide.
+   */
+  guide_props[PROP_MIN_WIDTH] =
+      g_param_spec_int ("min-width",
+                        "Minimum width",
+                        "Minimum width",
+                        0, G_MAXINT, 0,
+                        G_PARAM_READWRITE|
+                        G_PARAM_EXPLICIT_NOTIFY);
+  /**
+   * GtkConstraintGuide:min-height:
+   *
+   * The minimum height of the guide.
+   */
+  guide_props[PROP_MIN_HEIGHT] =
+      g_param_spec_int ("min-height",
+                        "Minimum height",
+                        "Minimum height",
+                        0, G_MAXINT, 0,
+                        G_PARAM_READWRITE|
+                        G_PARAM_EXPLICIT_NOTIFY);
+  /**
+   * GtkConstraintGuide:nat-width:
+   *
+   * The preferred, or natural, width of the guide.
+   */
+  guide_props[PROP_NAT_WIDTH] =
+      g_param_spec_int ("nat-width",
+                        "Natural width",
+                        "Natural width",
+                        0, G_MAXINT, 0,
+                        G_PARAM_READWRITE|
+                        G_PARAM_EXPLICIT_NOTIFY);
+  /**
+   * GtkConstraintGuide:nat-height:
+   *
+   * The preferred, or natural, height of the guide.
+   */
+  guide_props[PROP_NAT_HEIGHT] =
+      g_param_spec_int ("nat-height",
+                        "Natural height",
+                        "Natural height",
+                        0, G_MAXINT, 0,
+                        G_PARAM_READWRITE|
+                        G_PARAM_EXPLICIT_NOTIFY);
+  /**
+   * GtkConstraintGuide:max-width:
+   *
+   * The maximum width of the guide.
+   */
+  guide_props[PROP_MAX_WIDTH] =
+      g_param_spec_int ("max-width",
+                        "Maximum width",
+                        "Maximum width",
+                        0, G_MAXINT, G_MAXINT,
+                        G_PARAM_READWRITE|
+                        G_PARAM_EXPLICIT_NOTIFY);
+  /**
+   * GtkConstraintGuide:max-height:
+   *
+   * The maximum height of the guide.
+   */
+  guide_props[PROP_MAX_HEIGHT] =
+      g_param_spec_int ("max-height",
+                        "Maximum height",
+                        "Maximum height",
+                        0, G_MAXINT, G_MAXINT,
+                        G_PARAM_READWRITE|
+                        G_PARAM_EXPLICIT_NOTIFY);
+  /**
+   * GtkConstraintGuide:strength:
+   *
+   * The #GtkConstraintStrength to be used for the constraint on
+   * the natural size of the guide.
+   */
+  guide_props[PROP_STRENGTH] =
+      g_param_spec_enum ("strength",
+                         "Strength",
+                         "The strength to use for natural size",
+                         GTK_TYPE_CONSTRAINT_STRENGTH,
+                         GTK_CONSTRAINT_STRENGTH_MEDIUM,
+                         G_PARAM_READWRITE|
+                         G_PARAM_EXPLICIT_NOTIFY);
+  /**
+   * GtkConstraintGuide:name:
+   *
+   * A name that identifies the #GtkConstraintGuide, for debugging.
+   */
+  guide_props[PROP_NAME] =
+      g_param_spec_string ("name",
+                           "Name",
+                           "A name to use in debug message",
+                           NULL,
+                           G_PARAM_READWRITE);
+
+  g_object_class_install_properties (object_class, LAST_PROP, guide_props);
+}
+
+/**
+ * gtk_constraint_guide_new:
+ *
+ * Creates a new #GtkConstraintGuide object.
+ *
+ * Return: a new #GtkConstraintGuide object.
+ */
+GtkConstraintGuide *
+gtk_constraint_guide_new (void)
+{
+  return g_object_new (GTK_TYPE_CONSTRAINT_GUIDE, NULL);
+}
+
+/**
+ * gtk_constraint_guide_set_min_size:
+ * @guide: a #GtkConstraintGuide object
+ * @width: the new minimum width, or -1 to not change it
+ * @height: the new minimum height, or -1 to not change it
+ *
+ * Sets the minimum size of @guide.
+ *
+ * If @guide is attached to a #GtkConstraintLayout,
+ * the constraints will be updated to reflect the new size.
+ */
+void
+gtk_constraint_guide_set_min_size (GtkConstraintGuide *guide,
+                                   int                 width,
+                                   int                 height)
+{
+  g_return_if_fail (GTK_IS_CONSTRAINT_GUIDE (guide));
+  g_return_if_fail (width >= -1);
+  g_return_if_fail (height >= -1);
+
+  g_object_freeze_notify (G_OBJECT (guide));
+
+  if (width != -1)
+    g_object_set (guide, "min-width", width, NULL);
+
+  if (height != -1)
+    g_object_set (guide, "min-height", height, NULL);
+
+  g_object_thaw_notify (G_OBJECT (guide));
+}
+
+/**
+ * gtk_constraint_guide_get_min_size:
+ * @guide: a #GtkContraintGuide object
+ * @width: (allow-none): return location for the minimum width,
+ *     or %NULL
+ * @height: (allow-none): return location for the minimum height,
+ *     or %NULL
+ *
+ * Gets the minimum size of @guide.
+ */
+void
+gtk_constraint_guide_get_min_size (GtkConstraintGuide *guide,
+                                   int                *width,
+                                   int                *height)
+{
+  g_return_if_fail (GTK_IS_CONSTRAINT_GUIDE (guide));
+
+  if (width)
+    *width = guide->values[MIN_WIDTH];
+  if (height)
+    *height = guide->values[MIN_HEIGHT];
+}
+
+/**
+ * gtk_constraint_guide_set_nat_size:
+ * @guide: a #GtkConstraintGuide object
+ * @width: the new natural width, or -1 to not change it
+ * @height: the new natural height, or -1 to not change it
+ *
+ * Sets the natural size of @guide.
+ *
+ * If @guide is attached to a #GtkConstraintLayout,
+ * the constraints will be updated to reflect the new size.
+ */
+void
+gtk_constraint_guide_set_nat_size (GtkConstraintGuide *guide,
+                                   int                 width,
+                                   int                 height)
+{
+  g_return_if_fail (GTK_IS_CONSTRAINT_GUIDE (guide));
+  g_return_if_fail (width >= -1);
+  g_return_if_fail (height >= -1);
+
+  g_object_freeze_notify (G_OBJECT (guide));
+
+  if (width != -1)
+    g_object_set (guide, "nat-width", width, NULL);
+
+  if (height != -1)
+    g_object_set (guide, "nat-height", height, NULL);
+
+  g_object_thaw_notify (G_OBJECT (guide));
+}
+
+/**
+ * gtk_constraint_guide_get_nat_size:
+ * @guide: a #GtkContraintGuide object
+ * @width: (allow-none): return location for the natural width,
+ *     or %NULL
+ * @height: (allow-none): return location for the natural height,
+ *     or %NULL
+ *
+ * Gets the natural size of @guide.
+ */
+void
+gtk_constraint_guide_get_nat_size (GtkConstraintGuide *guide,
+                                   int                *width,
+                                   int                *height)
+{
+  g_return_if_fail (GTK_IS_CONSTRAINT_GUIDE (guide));
+
+  if (width)
+    *width = guide->values[NAT_WIDTH];
+  if (height)
+    *height = guide->values[NAT_HEIGHT];
+}
+
+/**
+ * gtk_constraint_guide_set_max_size:
+ * @guide: a #GtkConstraintGuide object
+ * @width: the new maximum width, or -1 to not change it
+ * @height: the new maximum height, or -1 to not change it
+ *
+ * Sets the maximum size of @guide.
+ *
+ * If @guide is attached to a #GtkConstraintLayout,
+ * the constraints will be updated to reflect the new size.
+ */
+void
+gtk_constraint_guide_set_max_size (GtkConstraintGuide *guide,
+                                   int                 width,
+                                   int                 height)
+{
+  g_return_if_fail (GTK_IS_CONSTRAINT_GUIDE (guide));
+  g_return_if_fail (width >= -1);
+  g_return_if_fail (height >= -1);
+
+  g_object_freeze_notify (G_OBJECT (guide));
+
+  if (width != -1)
+    g_object_set (guide, "max-width", width, NULL);
+
+  if (height != -1)
+    g_object_set (guide, "max-height", height, NULL);
+
+  g_object_thaw_notify (G_OBJECT (guide));
+}
+
+/**
+ * gtk_constraint_guide_get_max_size:
+ * @guide: a #GtkContraintGuide object
+ * @width: (allow-none): return location for the maximum width,
+ *     or %NULL
+ * @height: (allow-none): return location for the maximum height,
+ *     or %NULL
+ *
+ * Gets the maximum size of @guide.
+ */
+void
+gtk_constraint_guide_get_max_size (GtkConstraintGuide *guide,
+                                   int                *width,
+                                   int                *height)
+{
+  g_return_if_fail (GTK_IS_CONSTRAINT_GUIDE (guide));
+
+  if (width)
+    *width = guide->values[MAX_WIDTH];
+  if (height)
+    *height = guide->values[MAX_HEIGHT];
+}
+
+/**
+ * gtk_constraint_guide_get_name:
+ * @guide: a #GtkConstraintGuide
+ *
+ * Retrieves the name set using gtk_constraint_guide_set_name().
+ *
+ * Returns: (transfer none) (nullable): the name of the guide
+ */
+const char *
+gtk_constraint_guide_get_name (GtkConstraintGuide *guide)
+{
+  g_return_val_if_fail (GTK_IS_CONSTRAINT_GUIDE (guide), NULL);
+
+  return guide->name;
+}
+
+/**
+ * gtk_constraint_guide_set_name:
+ * @guide: a #GtkConstraintGuide
+ * @name: (nullable): a name for the @guide
+ *
+ * Sets a name for the given #GtkConstraintGuide.
+ *
+ * The name is useful for debugging purposes.
+ */
+void
+gtk_constraint_guide_set_name (GtkConstraintGuide *guide,
+                               const char         *name)
+{
+  g_return_if_fail (GTK_IS_CONSTRAINT_GUIDE (guide));
+
+  g_free (guide->name);
+  guide->name = g_strdup (name);
+  g_object_notify_by_pspec (G_OBJECT (guide), guide_props[PROP_NAME]);
+}
+
+/**
+ * gtk_constraint_guide_get_strength:
+ * @guide: a #GtkConstraintGuide
+ *
+ * Retrieves the strength set using gtk_constraint_guide_set_strength().
+ *
+ * Returns: the strength of the constraint on the natural size
+ */
+GtkConstraintStrength
+gtk_constraint_guide_get_strength (GtkConstraintGuide *guide)
+{
+  g_return_val_if_fail (GTK_IS_CONSTRAINT_GUIDE (guide),
+                        GTK_CONSTRAINT_STRENGTH_MEDIUM);
+
+  return guide->strength;
+}
+
+/**
+ * gtk_constraint_guide_set_strength:
+ * @guide: a #GtkConstraintGuide
+ * @strength: the strength of the constraint
+ *
+ * Sets the strength of the constraint on the natural size of the
+ * given #GtkConstraintGuide.
+ */
+void
+gtk_constraint_guide_set_strength (GtkConstraintGuide    *guide,
+                                   GtkConstraintStrength  strength)
+{
+  g_return_if_fail (GTK_IS_CONSTRAINT_GUIDE (guide));
+
+  if (guide->strength == strength)
+    return;
+
+  guide->strength = strength;
+  g_object_notify_by_pspec (G_OBJECT (guide), guide_props[PROP_STRENGTH]);
+  gtk_constraint_guide_update_constraint (guide, NAT_WIDTH);
+  gtk_constraint_guide_update_constraint (guide, NAT_HEIGHT);
+}

gtk/gtkconstraintguide.h

@@ -0,0 +1,83 @@
+/* gtkconstraintguide.h: Flexible space for constraints
+ * Copyright 2019 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Author: Matthias Clasen
+ */
+
+#pragma once
+
+#include <gtk/gtktypes.h>
+#include <gtk/gtkenums.h>
+#include <gtk/gtktypebuiltins.h>
+
+G_BEGIN_DECLS
+
+#define GTK_TYPE_CONSTRAINT_GUIDE (gtk_constraint_guide_get_type ())
+
+/**
+ * GtkConstraintGuide:
+ *
+ * An object that can be added to a #GtkConstraintLayout and be
+ * used in constraints like a widget, without being drawn.
+ *
+ * Guides have a minimum, maximum and natural size. Depending
+ * on the constraints that are applied, they can act like a
+ * guideline that widgets can be aligned to, or like 'flexible space'.
+ */
+GDK_AVAILABLE_IN_ALL
+G_DECLARE_FINAL_TYPE (GtkConstraintGuide, gtk_constraint_guide, GTK, CONSTRAINT_GUIDE, GObject)
+
+GDK_AVAILABLE_IN_ALL
+GtkConstraintGuide *    gtk_constraint_guide_new                (void);
+
+GDK_AVAILABLE_IN_ALL
+void                    gtk_constraint_guide_set_min_size       (GtkConstraintGuide *guide,
+                                                                 int                 width,
+                                                                 int                 height);
+GDK_AVAILABLE_IN_ALL
+void                    gtk_constraint_guide_get_min_size       (GtkConstraintGuide *guide,
+                                                                 int                *width,
+                                                                 int                *height);
+GDK_AVAILABLE_IN_ALL
+void                    gtk_constraint_guide_set_nat_size       (GtkConstraintGuide *guide,
+                                                                 int                 width,
+                                                                 int                 height);
+GDK_AVAILABLE_IN_ALL
+void                    gtk_constraint_guide_get_nat_size       (GtkConstraintGuide *guide,
+                                                                 int                *width,
+                                                                 int                *height);
+GDK_AVAILABLE_IN_ALL
+void                    gtk_constraint_guide_set_max_size       (GtkConstraintGuide *guide,
+                                                                 int                 width,
+                                                                 int                 height);
+GDK_AVAILABLE_IN_ALL
+void                    gtk_constraint_guide_get_max_size       (GtkConstraintGuide *guide,
+                                                                 int                *width,
+                                                                 int                *height);
+
+GDK_AVAILABLE_IN_ALL
+GtkConstraintStrength   gtk_constraint_guide_get_strength       (GtkConstraintGuide *guide);
+GDK_AVAILABLE_IN_ALL
+void                    gtk_constraint_guide_set_strength       (GtkConstraintGuide    *guide,
+                                                                 GtkConstraintStrength  strength);
+
+GDK_AVAILABLE_IN_ALL
+void                    gtk_constraint_guide_set_name           (GtkConstraintGuide *guide,
+                                                                 const char         *name);
+GDK_AVAILABLE_IN_ALL
+const char *            gtk_constraint_guide_get_name           (GtkConstraintGuide *guide);
+
+G_END_DECLS

gtk/gtkconstraintguideprivate.h

@@ -0,0 +1,38 @@
+/* gtkconstraintguideprivate.h: Constraint between two widgets
+ * Copyright 2019 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Author: Matthias Clasen
+ */
+
+#pragma once
+
+#include "gtkconstraintguide.h"
+#include "gtkconstraintlayout.h"
+#include "gtkconstrainttypesprivate.h"
+
+G_BEGIN_DECLS
+
+void                   gtk_constraint_guide_update        (GtkConstraintGuide     *guide);
+void                   gtk_constraint_guide_detach        (GtkConstraintGuide     *guide);
+
+GtkConstraintVariable *gtk_constraint_guide_get_attribute (GtkConstraintGuide      *guide,
+                                                           GtkConstraintAttribute  attr);
+
+GtkConstraintLayout   *gtk_constraint_guide_get_layout    (GtkConstraintGuide     *guide);
+void                   gtk_constraint_guide_set_layout    (GtkConstraintGuide     *guide,
+                                                           GtkConstraintLayout    *layout);
+
+G_END_DECLS

gtk/gtkconstraintlayout.h

@@ -0,0 +1,93 @@
+/* gtkconstraintlayout.h: Layout manager using constraints
+ * Copyright 2019  GNOME Foundation
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Author: Emmanuele Bassi
+ */
+#pragma once
+
+#include <gtk/gtklayoutmanager.h>
+#include <gtk/gtkconstraint.h>
+#include <gtk/gtkconstraintguide.h>
+
+G_BEGIN_DECLS
+
+#define GTK_TYPE_CONSTRAINT_LAYOUT (gtk_constraint_layout_get_type ())
+#define GTK_TYPE_CONSTRAINT_LAYOUT_CHILD (gtk_constraint_layout_child_get_type ())
+#define GTK_CONSTRAINT_VFL_PARSER_ERROR (gtk_constraint_vfl_parser_error_quark ())
+
+/**
+ * GtkConstraintLayoutChild:
+ *
+ * A #GtkLayoutChild in a #GtkConstraintLayout.
+ */
+GDK_AVAILABLE_IN_ALL
+G_DECLARE_FINAL_TYPE (GtkConstraintLayoutChild, gtk_constraint_layout_child, GTK, CONSTRAINT_LAYOUT_CHILD, GtkLayoutChild)
+
+/**
+ * GtkConstraintLayout:
+ *
+ * A layout manager using #GtkConstraint to describe
+ * relations between widgets.
+ */
+GDK_AVAILABLE_IN_ALL
+G_DECLARE_FINAL_TYPE (GtkConstraintLayout, gtk_constraint_layout, GTK, CONSTRAINT_LAYOUT, GtkLayoutManager)
+
+GDK_AVAILABLE_IN_ALL
+GQuark                  gtk_constraint_vfl_parser_error_quark   (void);
+
+GDK_AVAILABLE_IN_ALL
+GtkLayoutManager *      gtk_constraint_layout_new               (void);
+
+GDK_AVAILABLE_IN_ALL
+void                    gtk_constraint_layout_add_constraint    (GtkConstraintLayout *layout,
+                                                                 GtkConstraint       *constraint);
+GDK_AVAILABLE_IN_ALL
+void                    gtk_constraint_layout_remove_constraint (GtkConstraintLayout *layout,
+                                                                 GtkConstraint       *constraint);
+
+GDK_AVAILABLE_IN_ALL
+void                    gtk_constraint_layout_add_guide         (GtkConstraintLayout *layout,
+                                                                 GtkConstraintGuide  *guide);
+GDK_AVAILABLE_IN_ALL
+void                    gtk_constraint_layout_remove_guide      (GtkConstraintLayout *layout,
+                                                                 GtkConstraintGuide  *guide);
+GDK_AVAILABLE_IN_ALL
+void                    gtk_constraint_layout_remove_all_constraints            (GtkConstraintLayout *layout);
+
+GDK_AVAILABLE_IN_ALL
+GList *                 gtk_constraint_layout_add_constraints_from_description  (GtkConstraintLayout *layout,
+                                                                                 const char * const   lines[],
+                                                                                 gsize                n_lines,
+                                                                                 int                  hspacing,
+                                                                                 int                  vspacing,
+                                                                                 GError             **error,
+                                                                                 const char          *first_view,
+                                                                                 ...) G_GNUC_NULL_TERMINATED;
+GDK_AVAILABLE_IN_ALL
+GList *                 gtk_constraint_layout_add_constraints_from_descriptionv (GtkConstraintLayout *layout,
+                                                                                 const char * const   lines[],
+                                                                                 gsize                n_lines,
+                                                                                 int                  hspacing,
+                                                                                 int                  vspacing,
+                                                                                 GHashTable          *views,
+                                                                                 GError             **error);
+
+GDK_AVAILABLE_IN_ALL
+GListModel *          gtk_constraint_layout_observe_constraints (GtkConstraintLayout *layout);
+GDK_AVAILABLE_IN_ALL
+GListModel *          gtk_constraint_layout_observe_guides (GtkConstraintLayout *layout);
+
+G_END_DECLS

gtk/gtkconstraintlayoutprivate.h

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2019 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Author: Matthias Clasen
+ */
+
+#pragma once
+
+#include "gtkconstraintlayout.h"
+#include "gtkconstraintsolverprivate.h"
+
+G_BEGIN_DECLS
+
+GtkConstraintSolver *
+gtk_constraint_layout_get_solver (GtkConstraintLayout *layout);
+
+GtkConstraintVariable *
+gtk_constraint_layout_get_attribute (GtkConstraintLayout    *layout,
+                                     GtkConstraintAttribute  attr,
+                                     const char             *prefix,
+                                     GtkWidget              *widget,
+                                     GHashTable             *bound_attributes);
+
+G_END_DECLS

gtk/gtkconstraintprivate.h

@@ -0,0 +1,60 @@
+/* gtkconstraintprivate.h: Constraint between two widgets
+ * Copyright 2019  GNOME Foundation
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Author: Emmanuele Bassi
+ */
+
+#pragma once
+
+#include "gtkconstraint.h"
+#include "gtkconstrainttypesprivate.h"
+
+G_BEGIN_DECLS
+
+struct _GtkConstraint
+{
+  GObject parent_instance;
+
+  GtkConstraintAttribute target_attribute;
+  GtkConstraintAttribute source_attribute;
+
+  GtkConstraintTarget *target;
+  GtkConstraintTarget *source;
+
+  GtkConstraintRelation relation;
+
+  double multiplier;
+  double constant;
+
+  int strength;
+
+  /* A reference to the real constraint inside the
+   * GtkConstraintSolver, so we can remove it when
+   * finalizing the GtkConstraint instance
+   */
+  GtkConstraintRef *constraint_ref;
+
+  GtkConstraintSolver *solver;
+
+  guint active : 1;
+};
+
+void    gtk_constraint_attach           (GtkConstraint       *constraint,
+                                         GtkConstraintSolver *solver,
+                                         GtkConstraintRef    *ref);
+void    gtk_constraint_detach           (GtkConstraint       *constraint);
+
+G_END_DECLS

gtk/gtkconstraintsolverprivate.h

@@ -0,0 +1,117 @@
+/* gtkconstraintsolverprivate.h: Constraint solver based on the Cassowary method
+ * Copyright 2019  GNOME Foundation
+ *
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Author: Emmanuele Bassi
+ */
+
+#pragma once
+
+#include "gtkconstrainttypesprivate.h"
+
+G_BEGIN_DECLS
+
+#define GTK_TYPE_CONSTRAINT_SOLVER (gtk_constraint_solver_get_type())
+
+G_DECLARE_FINAL_TYPE (GtkConstraintSolver, gtk_constraint_solver, GTK, CONSTRAINT_SOLVER, GObject)
+
+GtkConstraintSolver *
+gtk_constraint_solver_new (void);
+
+void
+gtk_constraint_solver_freeze (GtkConstraintSolver *solver);
+
+void
+gtk_constraint_solver_thaw (GtkConstraintSolver *solver);
+
+void
+gtk_constraint_solver_resolve (GtkConstraintSolver *solver);
+
+GtkConstraintVariable *
+gtk_constraint_solver_create_variable (GtkConstraintSolver *solver,
+                                       const char          *prefix,
+                                       const char          *name,
+                                       double               value);
+
+GtkConstraintRef *
+gtk_constraint_solver_add_constraint (GtkConstraintSolver     *solver,
+                                      GtkConstraintVariable   *variable,
+                                      GtkConstraintRelation    relation,
+                                      GtkConstraintExpression *expression,
+                                      int                      strength);
+
+void
+gtk_constraint_solver_remove_constraint (GtkConstraintSolver *solver,
+                                         GtkConstraintRef    *reference);
+
+GtkConstraintRef *
+gtk_constraint_solver_add_stay_variable (GtkConstraintSolver   *solver,
+                                         GtkConstraintVariable *variable,
+                                         int                    strength);
+
+void
+gtk_constraint_solver_remove_stay_variable (GtkConstraintSolver   *solver,
+                                            GtkConstraintVariable *variable);
+
+gboolean
+gtk_constraint_solver_has_stay_variable (GtkConstraintSolver   *solver,
+                                         GtkConstraintVariable *variable);
+
+GtkConstraintRef *
+gtk_constraint_solver_add_edit_variable (GtkConstraintSolver   *solver,
+                                         GtkConstraintVariable *variable,
+                                         int                    strength);
+
+void
+gtk_constraint_solver_remove_edit_variable (GtkConstraintSolver   *solver,
+                                            GtkConstraintVariable *variable);
+
+gboolean
+gtk_constraint_solver_has_edit_variable (GtkConstraintSolver   *solver,
+                                         GtkConstraintVariable *variable);
+
+void
+gtk_constraint_solver_suggest_value (GtkConstraintSolver   *solver,
+                                     GtkConstraintVariable *variable,
+                                     double                 value);
+
+void
+gtk_constraint_solver_begin_edit (GtkConstraintSolver *solver);
+
+void
+gtk_constraint_solver_end_edit (GtkConstraintSolver *solver);
+
+void
+gtk_constraint_solver_note_added_variable (GtkConstraintSolver *self,
+                                           GtkConstraintVariable *variable,
+                                           GtkConstraintVariable *subject);
+
+void
+gtk_constraint_solver_note_removed_variable (GtkConstraintSolver *self,
+                                             GtkConstraintVariable *variable,
+                                             GtkConstraintVariable *subject);
+
+void
+gtk_constraint_solver_clear (GtkConstraintSolver *solver);
+
+char *
+gtk_constraint_solver_to_string (GtkConstraintSolver *solver);
+
+char *
+gtk_constraint_solver_statistics (GtkConstraintSolver *solver);
+
+G_END_DECLS

gtk/gtkconstrainttypesprivate.h

@@ -0,0 +1,50 @@
+/* gtkconstrainttypesprivate.h: Private types for the constraint solver
+ * Copyright 2019  GNOME Foundation
+ *
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Author: Emmanuele Bassi
+ */
+
+#pragma once
+
+#include <gtk/gtktypes.h>
+#include <gtk/gtkenums.h>
+
+G_BEGIN_DECLS
+
+typedef struct _GtkConstraintVariable           GtkConstraintVariable;
+typedef struct _GtkConstraintExpression         GtkConstraintExpression;
+typedef struct _GtkConstraintExpressionBuilder  GtkConstraintExpressionBuilder;
+
+/*< private >
+ * GtkConstraintRef:
+ *
+ * A reference to a constraint stored inside the solver; while #GtkConstraint
+ * represent the public API, a #GtkConstraintRef represents data stored inside
+ * the solver. A #GtkConstraintRef is completely opaque, and should only be
+ * used to remove a constraint from the solver.
+ */
+typedef struct _GtkConstraintRef                GtkConstraintRef;
+
+/*< private >
+ * GtkConstraintSolver:
+ *
+ * A simplex solver using the Cassowary constraint solving algorithm.
+ */
+typedef struct _GtkConstraintSolver             GtkConstraintSolver;
+
+G_END_DECLS

gtk/gtkconstraintvflparserprivate.h

@@ -0,0 +1,76 @@
+/* gtkconstraintvflparserprivate.h: VFL constraint definition parser 
+ *
+ * Copyright 2017  Endless
+ * Copyright 2019  GNOME Foundation
+ *
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "gtkconstrainttypesprivate.h"
+
+G_BEGIN_DECLS
+
+typedef struct _GtkConstraintVflParser       GtkConstraintVflParser;
+
+typedef struct {
+  const char *view1;
+  const char *attr1;
+  GtkConstraintRelation relation;
+  const char *view2;
+  const char *attr2;
+  double constant;
+  double multiplier;
+  double strength;
+} GtkConstraintVfl;
+
+GtkConstraintVflParser *
+gtk_constraint_vfl_parser_new (void);
+
+void
+gtk_constraint_vfl_parser_free (GtkConstraintVflParser *parser);
+
+void
+gtk_constraint_vfl_parser_set_default_spacing (GtkConstraintVflParser *parser,
+                                               int hspacing,
+                                               int vspacing);
+
+void
+gtk_constraint_vfl_parser_set_metrics (GtkConstraintVflParser *parser,
+                                       GHashTable *metrics);
+
+void
+gtk_constraint_vfl_parser_set_views (GtkConstraintVflParser *parser,
+                                     GHashTable *views);
+
+gboolean
+gtk_constraint_vfl_parser_parse_line (GtkConstraintVflParser *parser,
+                                      const char *line,
+                                      gssize len,
+                                      GError **error);
+
+int
+gtk_constraint_vfl_parser_get_error_offset (GtkConstraintVflParser *parser);
+
+int
+gtk_constraint_vfl_parser_get_error_range (GtkConstraintVflParser *parser);
+
+GtkConstraintVfl *
+gtk_constraint_vfl_parser_get_constraints (GtkConstraintVflParser *parser,
+                                           int *n_constraints);
+
+G_END_DECLS

gtk/gtkcssprovider.c

@@ -1118,6 +1118,8 @@ gtk_css_provider_load_internal (GtkCssProvider *self,
 
       if (parent == NULL)
         gtk_css_provider_postprocess (self);
+
+      g_bytes_unref (bytes);
     }
 }
 
@@ -1149,8 +1151,8 @@ gtk_css_provider_load_from_data (GtkCssProvider  *css_provider,
 
   gtk_css_provider_reset (css_provider);
 
+  g_bytes_ref (bytes);
   gtk_css_provider_load_internal (css_provider, NULL, NULL, bytes);
-
   g_bytes_unref (bytes);
 
   gtk_style_provider_changed (GTK_STYLE_PROVIDER (css_provider));

gtk/gtkdebug.h

@@ -51,7 +51,8 @@ typedef enum {
   GTK_DEBUG_ACTIONS         = 1 << 13,
   GTK_DEBUG_RESIZE          = 1 << 14,
   GTK_DEBUG_LAYOUT          = 1 << 15,
-  GTK_DEBUG_SNAPSHOT        = 1 << 16
+  GTK_DEBUG_SNAPSHOT        = 1 << 16,
+  GTK_DEBUG_CONSTRAINTS     = 1 << 17,
 } GtkDebugFlag;
 
 #ifdef G_ENABLE_DEBUG

gtk/gtkemojicompletion.c

@@ -566,7 +566,6 @@ populate_completion (GtkEmojiCompletion *completion,
   GVariantIter iter;
   GVariant *item;
 
-  text = g_strdup (text);
   g_free (completion->text);
   completion->text = g_strdup (text);
   completion->length = g_utf8_strlen (text, -1);

gtk/gtkentry.c

@@ -1529,6 +1529,7 @@ gtk_entry_measure (GtkWidget      *widget,
 {
   GtkEntry *entry = GTK_ENTRY (widget);
   GtkEntryPrivate *priv = gtk_entry_get_instance_private (entry);
+  int i;
 
   gtk_widget_measure (priv->text,
                       orientation,
@@ -1536,6 +1537,30 @@ gtk_entry_measure (GtkWidget      *widget,
                       minimum, natural,
                       minimum_baseline, natural_baseline);
 
+  for (i = 0; i < MAX_ICONS; i++)
+    {
+      EntryIconInfo *icon_info = priv->icons[i];
+      int icon_min, icon_nat;
+
+      if (!icon_info)
+        continue;
+
+      gtk_widget_measure (icon_info->widget,
+                          GTK_ORIENTATION_HORIZONTAL,
+                          -1, &icon_min, &icon_nat, NULL, NULL);
+
+      if (orientation == GTK_ORIENTATION_HORIZONTAL)
+        {
+          *minimum += icon_min;
+          *natural += icon_nat;
+        }
+      else
+        {
+          *minimum = MAX (*minimum, icon_min);
+          *natural = MAX (*natural, icon_nat);
+        }
+    }
+
   if (priv->progress_widget && gtk_widget_get_visible (priv->progress_widget))
     {
       int prog_min, prog_nat;

gtk/gtkenums.h

@@ -1053,4 +1053,98 @@ typedef enum {
   GTK_PICK_NON_TARGETABLE = 1 << 1
 } GtkPickFlags;
 
+/**
+ * GtkConstraintRelation:
+ * @GTK_CONSTRAINT_RELATION_EQ: Equal
+ * @GTK_CONSTRAINT_RELATION_LE: Less than, or equal
+ * @GTK_CONSTRAINT_RELATION_GE: Greater than, or equal
+ *
+ * The relation between two terms of a constraint.
+ */
+typedef enum {
+  GTK_CONSTRAINT_RELATION_LE = -1,
+  GTK_CONSTRAINT_RELATION_EQ = 0,
+  GTK_CONSTRAINT_RELATION_GE = 1
+} GtkConstraintRelation;
+
+/**
+ * GtkConstraintStrength:
+ * @GTK_CONSTRAINT_STRENGTH_REQUIRED: The constraint is required towards solving the layout
+ * @GTK_CONSTRAINT_STRENGTH_STRONG: A strong constraint
+ * @GTK_CONSTRAINT_STRENGTH_MEDIUM: A medium constraint
+ * @GTK_CONSTRAINT_STRENGTH_WEAK: A weak constraint
+ *
+ * The strength of a constraint, expressed as a symbolic constant.
+ *
+ * The strength of a #GtkConstraint can be expressed with any positive
+ * integer; the values of this enumeration can be used for readability.
+ */
+typedef enum {
+  GTK_CONSTRAINT_STRENGTH_REQUIRED = 1001001000,
+  GTK_CONSTRAINT_STRENGTH_STRONG   = 1000000000,
+  GTK_CONSTRAINT_STRENGTH_MEDIUM   = 1000,
+  GTK_CONSTRAINT_STRENGTH_WEAK     = 1
+} GtkConstraintStrength;
+
+/**
+ * GtkConstraintAttribute:
+ * @GTK_CONSTRAINT_ATTRIBUTE_NONE: No attribute, used for constant
+ *   relations
+ * @GTK_CONSTRAINT_ATTRIBUTE_LEFT: The left edge of a widget, regardless of
+ *   text direction
+ * @GTK_CONSTRAINT_ATTRIBUTE_RIGHT: The right edge of a widget, regardless
+ *   of text direction
+ * @GTK_CONSTRAINT_ATTRIBUTE_TOP: The top edge of a widget
+ * @GTK_CONSTRAINT_ATTRIBUTE_BOTTOM: The bottom edge of a widget
+ * @GTK_CONSTRAINT_ATTRIBUTE_START: The leading edge of a widget, depending
+ *   on text direction; equivalent to %GTK_CONSTRAINT_ATTRIBUTE_LEFT for LTR
+ *   languages, and %GTK_CONSTRAINT_ATTRIBUTE_RIGHT for RTL ones
+ * @GTK_CONSTRAINT_ATTRIBUTE_END: The trailing edge of a widget, depending
+ *   on text direction; equivalent to %GTK_CONSTRAINT_ATTRIBUTE_RIGHT for LTR
+ *   languages, and %GTK_CONSTRAINT_ATTRIBUTE_LEFT for RTL ones
+ * @GTK_CONSTRAINT_ATTRIBUTE_WIDTH: The width of a widget
+ * @GTK_CONSTRAINT_ATTRIBUTE_HEIGHT: The height of a widget
+ * @GTK_CONSTRAINT_ATTRIBUTE_CENTER_X: The center of a widget, on the
+ *   horizontal axis
+ * @GTK_CONSTRAINT_ATTRIBUTE_CENTER_Y: The center of a widget, on the
+ *   vertical axis
+ * @GTK_CONSTRAINT_ATTRIBUTE_BASELINE: The baseline of a widget
+ *
+ * The widget attributes that can be used when creating a #GtkConstraint.
+ */
+typedef enum {
+  GTK_CONSTRAINT_ATTRIBUTE_NONE,
+  GTK_CONSTRAINT_ATTRIBUTE_LEFT,
+  GTK_CONSTRAINT_ATTRIBUTE_RIGHT,
+  GTK_CONSTRAINT_ATTRIBUTE_TOP,
+  GTK_CONSTRAINT_ATTRIBUTE_BOTTOM,
+  GTK_CONSTRAINT_ATTRIBUTE_START,
+  GTK_CONSTRAINT_ATTRIBUTE_END,
+  GTK_CONSTRAINT_ATTRIBUTE_WIDTH,
+  GTK_CONSTRAINT_ATTRIBUTE_HEIGHT,
+  GTK_CONSTRAINT_ATTRIBUTE_CENTER_X,
+  GTK_CONSTRAINT_ATTRIBUTE_CENTER_Y,
+  GTK_CONSTRAINT_ATTRIBUTE_BASELINE
+} GtkConstraintAttribute;
+
+/**
+ * GtkConstraintVflParserError:
+ * @GTK_CONSTRAINT_VFL_PARSER_ERROR_INVALID_SYMBOL: Invalid or unknown symbol
+ * @GTK_CONSTRAINT_VFL_PARSER_ERROR_INVALID_ATTRIBUTE: Invalid or unknown attribute
+ * @GTK_CONSTRAINT_VFL_PARSER_ERROR_INVALID_VIEW: Invalid or unknown view
+ * @GTK_CONSTRAINT_VFL_PARSER_ERROR_INVALID_METRIC: Invalid or unknown metric
+ * @GTK_CONSTRAINT_VFL_PARSER_ERROR_INVALID_PRIORITY: Invalid or unknown priority
+ * @GTK_CONSTRAINT_VFL_PARSER_ERROR_INVALID_RELATION: Invalid or unknown relation
+ *
+ * Domain for VFL parsing errors.
+ */
+typedef enum {
+  GTK_CONSTRAINT_VFL_PARSER_ERROR_INVALID_SYMBOL,
+  GTK_CONSTRAINT_VFL_PARSER_ERROR_INVALID_ATTRIBUTE,
+  GTK_CONSTRAINT_VFL_PARSER_ERROR_INVALID_VIEW,
+  GTK_CONSTRAINT_VFL_PARSER_ERROR_INVALID_METRIC,
+  GTK_CONSTRAINT_VFL_PARSER_ERROR_INVALID_PRIORITY,
+  GTK_CONSTRAINT_VFL_PARSER_ERROR_INVALID_RELATION
+} GtkConstraintVflParserError;
+
 #endif /* __GTK_ENUMS_H__ */

gtk/gtkfilechooserdialog.c

@@ -577,9 +577,34 @@ gtk_file_chooser_dialog_map (GtkWidget *widget)
   GTK_WIDGET_CLASS (gtk_file_chooser_dialog_parent_class)->map (widget);
 }
 
+static void
+save_dialog_geometry (GtkFileChooserDialog *dialog)
+{
+  GtkWindow *window;
+  GSettings *settings;
+  int old_width, old_height;
+  int width, height;
+
+  settings = _gtk_file_chooser_get_settings_for_widget (GTK_WIDGET (dialog));
+
+  window = GTK_WINDOW (dialog);
+
+  gtk_window_get_size (window, &width, &height);
+
+  g_settings_get (settings, SETTINGS_KEY_WINDOW_SIZE, "(ii)", &old_width, &old_height);
+  if (old_width != width || old_height != height)
+    g_settings_set (settings, SETTINGS_KEY_WINDOW_SIZE, "(ii)", width, height);
+
+  g_settings_apply (settings);
+}
+
 static void
 gtk_file_chooser_dialog_unmap (GtkWidget *widget)
 {
+  GtkFileChooserDialog *dialog = GTK_FILE_CHOOSER_DIALOG (widget);
+
+  save_dialog_geometry (dialog);
+
   GTK_WIDGET_CLASS (gtk_file_chooser_dialog_parent_class)->unmap (widget);
 }
 
@@ -593,6 +618,8 @@ gtk_file_chooser_dialog_size_allocate (GtkWidget *widget,
                                                                           width,
                                                                           height,
                                                                           baseline);
+  if (gtk_widget_is_drawable (widget))
+    save_dialog_geometry (GTK_FILE_CHOOSER_DIALOG (widget));
 }
 
 /* We do a signal connection here rather than overriding the method in

gtk/gtkfilechooserwidget.c

@@ -2460,19 +2460,6 @@ location_changed_timeout_cb (gpointer user_data)
   return G_SOURCE_REMOVE;
 }
 
-static void
-reset_location_timeout (GtkFileChooserWidget *impl)
-{
-  GtkFileChooserWidgetPrivate *priv = gtk_file_chooser_widget_get_instance_private (impl);
-
-  if (priv->location_changed_id > 0)
-    g_source_remove (priv->location_changed_id);
-  priv->location_changed_id = g_timeout_add (LOCATION_CHANGED_TIMEOUT,
-                                            location_changed_timeout_cb,
-                                            impl);
-  g_source_set_name_by_id (priv->location_changed_id, "[gtk] location_changed_timeout_cb");
-}
-
 static void
 location_entry_changed_cb (GtkEditable          *editable,
                            GtkFileChooserWidget *impl)
@@ -2489,7 +2476,16 @@ location_entry_changed_cb (GtkEditable          *editable,
     }
 
   if (priv->action != GTK_FILE_CHOOSER_ACTION_SELECT_FOLDER)
-    reset_location_timeout (impl);
+    {
+      /* Reset location timeout */
+      if (priv->location_changed_id > 0)
+        g_source_remove (priv->location_changed_id);
+
+      priv->location_changed_id = g_timeout_add (LOCATION_CHANGED_TIMEOUT,
+                                                location_changed_timeout_cb,
+                                                impl);
+      g_source_set_name_by_id (priv->location_changed_id, "[gtk] location_changed_timeout_cb");
+    }
 }
 
 static void
@@ -3051,12 +3047,20 @@ static void
 operation_mode_set_browse (GtkFileChooserWidget *impl)
 {
   GtkFileChooserWidgetPrivate *priv = gtk_file_chooser_widget_get_instance_private (impl);
+  GtkRevealerTransitionType old_revealer_transition_type;
 
   gtk_places_sidebar_set_location (GTK_PLACES_SIDEBAR (priv->places_sidebar), priv->current_folder);
   gtk_stack_set_visible_child_name (GTK_STACK (priv->browse_files_stack), "list");
   location_mode_set (impl, LOCATION_MODE_PATH_BAR);
   gtk_stack_set_visible_child_name (GTK_STACK (priv->browse_header_stack), "pathbar");
+
+  old_revealer_transition_type = gtk_revealer_get_transition_type (GTK_REVEALER (priv->browse_header_revealer));
+  gtk_revealer_set_transition_type (GTK_REVEALER (priv->browse_header_revealer),
+                                    GTK_REVEALER_TRANSITION_TYPE_NONE);
   gtk_revealer_set_reveal_child (GTK_REVEALER (priv->browse_header_revealer), TRUE);
+  gtk_revealer_set_transition_type (GTK_REVEALER (priv->browse_header_revealer),
+                                    old_revealer_transition_type);
+
   gtk_widget_set_sensitive (priv->filter_combo, TRUE);
   g_object_notify (G_OBJECT (impl), "subtitle");
 }
@@ -3090,10 +3094,19 @@ operation_mode_set_recent (GtkFileChooserWidget *impl)
 {
   GtkFileChooserWidgetPrivate *priv = gtk_file_chooser_widget_get_instance_private (impl);
   GFile *file;
+  GtkRevealerTransitionType old_revealer_transition_type;
 
   gtk_stack_set_visible_child_name (GTK_STACK (priv->browse_files_stack), "list");
   gtk_stack_set_visible_child_name (GTK_STACK (priv->browse_header_stack), "pathbar");
+
+  /* Hide browse_header without a transition */
+  old_revealer_transition_type = gtk_revealer_get_transition_type (GTK_REVEALER (priv->browse_header_revealer));
+  gtk_revealer_set_transition_type (GTK_REVEALER (priv->browse_header_revealer),
+                                    GTK_REVEALER_TRANSITION_TYPE_NONE);
   gtk_revealer_set_reveal_child (GTK_REVEALER (priv->browse_header_revealer), FALSE);
+  gtk_revealer_set_transition_type (GTK_REVEALER (priv->browse_header_revealer),
+                                    old_revealer_transition_type);
+
   location_bar_update (impl);
   recent_start_loading (impl);
   file = g_file_new_for_uri ("recent:///");
@@ -3584,7 +3597,6 @@ gtk_file_chooser_widget_unroot (GtkWidget *widget)
 
   remove_settings_signal (impl, gtk_widget_get_display (widget));
   check_icon_theme (impl);
-  emit_default_size_changed (impl);
 
   GTK_WIDGET_CLASS (gtk_file_chooser_widget_parent_class)->unroot (widget);
 }

gtk/gtkflattenlistmodel.c

@@ -216,17 +216,25 @@ gtk_flatten_list_model_items_changed_cb (GListModel          *model,
                                          guint                added,
                                          gpointer             _node)
 {
-  FlattenNode *node = _node, *parent;
+  FlattenNode *node = _node, *parent, *left;
   GtkFlattenListModel *self = node->list;
   guint real_position;
 
   gtk_rb_tree_node_mark_dirty (node);
+  real_position = position;
 
-  for (real_position = position;
+  left = gtk_rb_tree_node_get_left (node);
+  if (left)
+    {
+      FlattenAugment *aug = gtk_rb_tree_get_augment (self->items, left);
+      real_position += aug->n_items;
+    }
+
+  for (;
        (parent = gtk_rb_tree_node_get_parent (node)) != NULL;
        node = parent)
     {
-      FlattenNode *left = gtk_rb_tree_node_get_left (parent);
+      left = gtk_rb_tree_node_get_left (parent);
       if (left != node)
         {
           if (left)

gtk/gtkgridlayout.c

@@ -212,6 +212,8 @@ gtk_grid_layout_child_class_init (GtkGridLayoutChildClass *klass)
 static void
 gtk_grid_layout_child_init (GtkGridLayoutChild *self)
 {
+  CHILD_ROW_SPAN (self) = 1;
+  CHILD_COL_SPAN (self) = 1;
 }
 
 /**

gtk/gtkheaderbar.c

@@ -1356,7 +1356,6 @@ gtk_header_bar_set_custom_title (GtkHeaderBar *bar,
 
       gtk_header_bar_reorder_css_node (bar, GTK_PACK_START, priv->custom_title);
       gtk_widget_set_parent (priv->custom_title, GTK_WIDGET (bar));
-      gtk_widget_set_valign (priv->custom_title, GTK_ALIGN_CENTER);
 
       if (priv->label_box != NULL)
         {

gtk/gtkiconhelper.c

@@ -227,19 +227,35 @@ gtk_icon_helper_paintable_snapshot (GdkPaintable *paintable,
         h = MIN (h, height);
         x = (width - w) / 2;
         y = (height - h) / 2;
-        gtk_snapshot_save (snapshot);
-        gtk_snapshot_translate (snapshot, &GRAPHENE_POINT_INIT (x, y));
-        gtk_css_style_snapshot_icon_paintable (style,
-                                               snapshot,
-                                               self->paintable,
-                                               w, h,
-                                               self->texture_is_symbolic);
-        gtk_snapshot_restore (snapshot);
+
+        if (x  != 0 || y != 0)
+          {
+            gtk_snapshot_save (snapshot);
+            gtk_snapshot_translate (snapshot, &GRAPHENE_POINT_INIT (x, y));
+            gtk_css_style_snapshot_icon_paintable (style,
+                                                   snapshot,
+                                                   self->paintable,
+                                                   w, h,
+                                                   self->texture_is_symbolic);
+            gtk_snapshot_restore (snapshot);
+          }
+        else
+          {
+            gtk_css_style_snapshot_icon_paintable (style,
+                                                   snapshot,
+                                                   self->paintable,
+                                                   w, h,
+                                                   self->texture_is_symbolic);
+
+          }
+
       }
       break;
 
-    case GTK_IMAGE_PAINTABLE:
     case GTK_IMAGE_EMPTY:
+      break;
+
+    case GTK_IMAGE_PAINTABLE:
     default:
       {
         double image_ratio = (double) width / height;
@@ -269,14 +285,25 @@ gtk_icon_helper_paintable_snapshot (GdkPaintable *paintable,
         x = floor (width - ceil (w)) / 2;
         y = floor (height - ceil (h)) / 2;
 
-        gtk_snapshot_save (snapshot);
-        gtk_snapshot_translate (snapshot, &GRAPHENE_POINT_INIT (x, y));
-        gtk_css_style_snapshot_icon_paintable (style,
-                                               snapshot,
-                                               self->paintable,
-                                               w, h,
-                                               self->texture_is_symbolic);
-        gtk_snapshot_restore (snapshot);
+        if (x != 0 || y != 0)
+          {
+            gtk_snapshot_save (snapshot);
+            gtk_snapshot_translate (snapshot, &GRAPHENE_POINT_INIT (x, y));
+            gtk_css_style_snapshot_icon_paintable (style,
+                                                   snapshot,
+                                                   self->paintable,
+                                                   w, h,
+                                                   self->texture_is_symbolic);
+            gtk_snapshot_restore (snapshot);
+          }
+        else
+          {
+            gtk_css_style_snapshot_icon_paintable (style,
+                                                   snapshot,
+                                                   self->paintable,
+                                                   w, h,
+                                                   self->texture_is_symbolic);
+          }
       }
       break;
     }

gtk/gtklayoutmanager.c

@@ -91,6 +91,7 @@
 
 typedef struct {
   GtkWidget *widget;
+  GtkRoot *root;
 
   /* HashTable<Widget, LayoutChild> */
   GHashTable *layout_children;
@@ -98,6 +99,16 @@ typedef struct {
 
 G_DEFINE_ABSTRACT_TYPE_WITH_PRIVATE (GtkLayoutManager, gtk_layout_manager, G_TYPE_OBJECT)
 
+static void
+gtk_layout_manager_real_root (GtkLayoutManager *manager)
+{
+}
+
+static void
+gtk_layout_manager_real_unroot (GtkLayoutManager *manager)
+{
+}
+
 static GtkSizeRequestMode
 gtk_layout_manager_real_get_request_mode (GtkLayoutManager *manager,
                                           GtkWidget        *widget)
@@ -188,13 +199,30 @@ gtk_layout_manager_real_create_layout_child (GtkLayoutManager *manager,
                        NULL);
 }
 
+static void
+gtk_layout_manager_finalize (GObject *gobject)
+{
+  GtkLayoutManager *self = GTK_LAYOUT_MANAGER (gobject);
+  GtkLayoutManagerPrivate *priv = gtk_layout_manager_get_instance_private (self);
+
+  g_clear_pointer (&priv->layout_children, g_hash_table_unref);
+
+  G_OBJECT_CLASS (gtk_layout_manager_parent_class)->finalize (gobject);
+}
+
 static void
 gtk_layout_manager_class_init (GtkLayoutManagerClass *klass)
 {
+  GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
+
+  gobject_class->finalize = gtk_layout_manager_finalize;
+
   klass->get_request_mode = gtk_layout_manager_real_get_request_mode;
   klass->measure = gtk_layout_manager_real_measure;
   klass->allocate = gtk_layout_manager_real_allocate;
   klass->create_layout_child = gtk_layout_manager_real_create_layout_child;
+  klass->root = gtk_layout_manager_real_root;
+  klass->unroot = gtk_layout_manager_real_unroot;
 }
 
 static void
@@ -226,6 +254,38 @@ gtk_layout_manager_set_widget (GtkLayoutManager *layout_manager,
     }
 
   priv->widget = widget;
+
+  if (widget != NULL)
+    gtk_layout_manager_set_root (layout_manager, gtk_widget_get_root (widget));
+}
+
+/*< private >
+ * gtk_layout_manager_set_root:
+ * @layout_manager: a #GtkLayoutManager
+ * @root: (nullable): a #GtkWidget implementing #GtkRoot
+ *
+ * Sets a back pointer from @root to @layout_manager.
+ *
+ * This function is called by #GtkWidget when getting rooted and unrooted,
+ * and will call #GtkLayoutManagerClass.root() or #GtkLayoutManagerClass.unroot()
+ * depending on whether @root is a #GtkWidget or %NULL.
+ */
+void
+gtk_layout_manager_set_root (GtkLayoutManager *layout_manager,
+                             GtkRoot          *root)
+{
+  GtkLayoutManagerPrivate *priv = gtk_layout_manager_get_instance_private (layout_manager);
+  GtkRoot *old_root = priv->root;
+
+  priv->root = root;
+
+  if (old_root != root)
+    {
+      if (priv->root != NULL)
+        GTK_LAYOUT_MANAGER_GET_CLASS (layout_manager)->root (layout_manager);
+      else
+        GTK_LAYOUT_MANAGER_GET_CLASS (layout_manager)->unroot (layout_manager);
+    }
 }
 
 /**

gtk/gtklayoutmanager.h

@@ -42,6 +42,10 @@ G_DECLARE_DERIVABLE_TYPE (GtkLayoutManager, gtk_layout_manager, GTK, LAYOUT_MANA
  * @layout_child_type: the type of #GtkLayoutChild used by this layout manager
  * @create_layout_child: a virtual function, used to create a #GtkLayoutChild
  *   meta object for the layout properties
+ * @root: a virtual function, called when the widget using the layout
+ *   manager is attached to a #GtkRoot
+ * @unroot: a virtual function, called when the widget using the layout
+ *   manager is detached from a #GtkRoot
  *
  * The `GtkLayoutManagerClass` structure contains only private data, and
  * should only be accessed through the provided API, or when subclassing
@@ -77,6 +81,9 @@ struct _GtkLayoutManagerClass
                                               GtkWidget        *widget,
                                               GtkWidget        *for_child);
 
+  void               (* root)                (GtkLayoutManager *manager);
+  void               (* unroot)              (GtkLayoutManager *manager);
+
   /*< private >*/
   gpointer _padding[16];
 };

gtk/gtklayoutmanagerprivate.h

@@ -10,4 +10,7 @@ void gtk_layout_manager_set_widget (GtkLayoutManager *manager,
 void gtk_layout_manager_remove_layout_child (GtkLayoutManager *manager,
                                              GtkWidget        *widget);
 
+void gtk_layout_manager_set_root (GtkLayoutManager *manager,
+                                  GtkRoot          *root);
+
 G_END_DECLS

gtk/gtkmain.c

@@ -179,7 +179,8 @@ static const GDebugKey gtk_debug_keys[] = {
   { "actions", GTK_DEBUG_ACTIONS },
   { "resize", GTK_DEBUG_RESIZE },
   { "layout", GTK_DEBUG_LAYOUT },
-  { "snapshot", GTK_DEBUG_SNAPSHOT }
+  { "snapshot", GTK_DEBUG_SNAPSHOT },
+  { "constraints", GTK_DEBUG_CONSTRAINTS },
 };
 #endif /* G_ENABLE_DEBUG */
 

gtk/gtkmenu.c

@@ -1757,7 +1757,7 @@ GtkWidget*
 gtk_menu_get_active (GtkMenu *menu)
 {
   GtkMenuPrivate *priv;
-  GtkWidget *child;
+  GtkWidget *child = NULL;
   GList *children, *l;
 
   g_return_val_if_fail (GTK_IS_MENU (menu), NULL);
@@ -2414,7 +2414,6 @@ gtk_menu_position (GtkMenu *menu)
   GdkAnchorHints anchor_hints;
   gint rect_anchor_dx, rect_anchor_dy;
   GdkSurface *toplevel;
-  gboolean emulated_move_to_rect = FALSE;
 
   rect_anchor = priv->rect_anchor;
   menu_anchor = priv->menu_anchor;
@@ -2461,10 +2460,8 @@ gtk_menu_position (GtkMenu *menu)
 
   g_signal_handlers_disconnect_by_func (toplevel, moved_to_rect_cb, menu);
 
-  if (!emulated_move_to_rect)
-    g_signal_connect (toplevel, "moved-to-rect", G_CALLBACK (moved_to_rect_cb),
-                      menu);
-
+  g_signal_connect (toplevel, "moved-to-rect", G_CALLBACK (moved_to_rect_cb),
+                    menu);
 
   gdk_surface_move_to_rect (toplevel,
                            &rect,