curve2: Show osculating circles

This one is for interactive exploring of svg paths.

You can enter an SVG path in the entry and hit Enter
to see how GSK renders it. If you click the button
in the headerbar, you can see what GTK thinks the
closest point, tangent and distance are wrt. to the
mouse position, and the bounding box of the path.

There's also stroke parameters to play with.

gsk/gskcontour.c

@@ -62,6 +62,10 @@ struct _GskContourClass
                                                  float                   distance,
                                                  graphene_point_t       *pos,
                                                  graphene_vec2_t        *tangent);
+  float                 (* get_curvature)       (const GskContour       *contour,
+                                                 gpointer                measure_data,
+                                                 float                   distance,
+                                                 graphene_point_t       *center);
   gboolean              (* get_closest_point)   (const GskContour       *contour,
                                                  gpointer                measure_data,
                                                  float                   tolerance,
@@ -301,6 +305,15 @@ gsk_rect_contour_get_point (const GskContour *contour,
     graphene_vec2_init (tangent, 0.0f, - copysignf (self->height, 1.0f));
 }
 
+static float
+gsk_rect_contour_get_curvature (const GskContour *contour,
+                                gpointer          measure_data,
+                                float             distance,
+                                graphene_point_t *center)
+{
+  return 0;
+}
+
 static gboolean
 gsk_rect_contour_get_closest_point (const GskContour       *contour,
                                     gpointer                measure_data,
@@ -564,6 +577,7 @@ static const GskContourClass GSK_RECT_CONTOUR_CLASS =
   gsk_rect_contour_init_measure,
   gsk_rect_contour_free_measure,
   gsk_rect_contour_get_point,
+  gsk_rect_contour_get_curvature,
   gsk_rect_contour_get_closest_point,
   gsk_rect_contour_copy,
   gsk_rect_contour_add_segment,
@@ -765,6 +779,20 @@ gsk_circle_contour_get_point (const GskContour *contour,
     }
 }
 
+static float
+gsk_circle_contour_get_curvature (const GskContour *contour,
+                                  gpointer          measure_data,
+                                  float             distance,
+                                  graphene_point_t *center)
+{
+  const GskCircleContour *self = (const GskCircleContour *) contour;
+
+  if (center)
+    *center = self->center;
+
+  return 1 / self->radius;
+}
+
 static gboolean
 gsk_circle_contour_get_closest_point (const GskContour       *contour,
                                       gpointer                measure_data,
@@ -950,6 +978,7 @@ static const GskContourClass GSK_CIRCLE_CONTOUR_CLASS =
   gsk_circle_contour_init_measure,
   gsk_circle_contour_free_measure,
   gsk_circle_contour_get_point,
+  gsk_circle_contour_get_curvature,
   gsk_circle_contour_get_closest_point,
   gsk_circle_contour_copy,
   gsk_circle_contour_add_segment,
@@ -1286,6 +1315,38 @@ gsk_standard_contour_get_point (const GskContour *contour,
     gsk_curve_get_tangent (&curve, progress, tangent);
 }
 
+static float
+gsk_standard_contour_get_curvature (const GskContour *contour,
+                                    gpointer          measure_data,
+                                    float             distance,
+                                    graphene_point_t *center)
+{
+  GskStandardContour *self = (GskStandardContour *) contour;
+  GArray *array = measure_data;
+  guint index;
+  float progress;
+  GskStandardContourMeasure *measure;
+  GskCurve curve;
+
+  if (array->len == 0)
+    {
+      g_assert (distance == 0);
+      g_assert (gsk_pathop_op (self->ops[0]) == GSK_PATH_MOVE);
+      return 0;
+    }
+
+  if (!g_array_binary_search (array, &distance, gsk_standard_contour_find_measure, &index))
+    index = array->len - 1;
+  measure = &g_array_index (array, GskStandardContourMeasure, index);
+  progress = (distance - measure->start) / (measure->end - measure->start);
+  progress = measure->start_progress + (measure->end_progress - measure->start_progress) * progress;
+  g_assert (progress >= 0 && progress <= 1);
+
+  gsk_curve_init (&curve, self->ops[measure->op]);
+
+  return gsk_curve_get_curvature (&curve, progress, center);
+}
+
 static gboolean
 gsk_standard_contour_get_closest_point (const GskContour       *contour,
                                         gpointer                measure_data,
@@ -1675,6 +1736,7 @@ static const GskContourClass GSK_STANDARD_CONTOUR_CLASS =
   gsk_standard_contour_init_measure,
   gsk_standard_contour_free_measure,
   gsk_standard_contour_get_point,
+  gsk_standard_contour_get_curvature,
   gsk_standard_contour_get_closest_point,
   gsk_standard_contour_copy,
   gsk_standard_contour_add_segment,
@@ -1803,6 +1865,15 @@ gsk_contour_get_point (const GskContour *self,
   self->klass->get_point (self, measure_data, distance, pos, tangent);
 }
 
+float
+gsk_contour_get_curvature (const GskContour *self,
+                           gpointer          measure_data,
+                           float             distance,
+                           graphene_point_t *center)
+{
+  return self->klass->get_curvature (self, measure_data, distance, center);
+}
+
 gboolean
 gsk_contour_get_closest_point (const GskContour       *self,
                                gpointer                measure_data,

gsk/gskcontourprivate.h

@@ -74,6 +74,10 @@ void                    gsk_contour_get_point                   (const GskContou
                                                                  float                   distance,
                                                                  graphene_point_t       *pos,
                                                                  graphene_vec2_t        *tangent);
+float                   gsk_contour_get_curvature               (const GskContour       *self,
+                                                                 gpointer                measure_data,
+                                                                 float                   distance,
+                                                                 graphene_point_t       *center);
 gboolean                gsk_contour_get_closest_point           (const GskContour       *self,
                                                                  gpointer                measure_data,
                                                                  float                   tolerance,

gsk/gskpathmeasure.c

@@ -377,6 +377,59 @@ gsk_path_measure_get_point (GskPathMeasure   *self,
                          tangent);
 }
 
+/**
+ * @self: a #GskPathMeasure
+ * @distance: distance into the path
+ * @center: (out) (optional) (caller-allocates): The center
+ *      of the osculating circle at the point
+ *
+ * Calculates the curvature at the point @distance units into
+ * the path. Optionally, returns the center of the osculating
+ * circle as well.
+ *
+ * If the curvature is infinite (at line segments), or does
+ * not exist (at sharp turns), zero is returned, and @center
+ * is not modified.
+ *
+ * Returns: The curvature of the path at the given point
+ */
+float
+gsk_path_measure_get_curvature (GskPathMeasure   *self,
+                                float             distance,
+                                graphene_point_t *center)
+{
+  gsize i;
+
+  g_return_val_if_fail (self != NULL, 0);
+
+  distance = gsk_path_measure_clamp_distance (self, distance);
+
+  for (i = self->first; i < self->last; i++)
+    {
+      if (distance < self->measures[i].length)
+        break;
+
+      distance -= self->measures[i].length;
+    }
+
+  /* weird corner cases */
+  if (i == self->last)
+    {
+      /* the empty path goes here */
+      if (self->first == self->last)
+        return 0;
+
+      /* rounding errors can make this happen */
+      i = self->last - 1;
+      distance = self->measures[i].length;
+    }
+
+  return gsk_contour_get_curvature (gsk_path_get_contour (self->path, i),
+                                    self->measures[i].contour_data,
+                                    distance,
+                                    center);
+}
+
 /**
  * gsk_path_measure_get_closest_point:
  * @self: a #GskPathMeasure

gsk/gskpathmeasure.h

@@ -65,6 +65,11 @@ void                    gsk_path_measure_get_point              (GskPathMeasure
                                                                  graphene_point_t       *pos,
                                                                  graphene_vec2_t        *tangent);
 GDK_AVAILABLE_IN_ALL
+float                   gsk_path_measure_get_curvature          (GskPathMeasure         *self,
+                                                                 float                   distance,
+                                                                 graphene_point_t       *center);
+
+GDK_AVAILABLE_IN_ALL
 float                   gsk_path_measure_get_closest_point      (GskPathMeasure         *self,
                                                                  const graphene_point_t *point,
                                                                  graphene_point_t       *out_pos);

gsk/gskstroke.c

@@ -111,6 +111,14 @@ gsk_stroke_free (GskStroke *self)
   g_free (self);
 }
 
+/**
+ * gsk_stroke_to_cairo:
+ * @self: a #GskStroke
+ * @cr: the cairo context to configure
+ *
+ * A helper function that sets the stroke parameters
+ * of @cr from the values found in @self.
+ */
 void
 gsk_stroke_to_cairo (const GskStroke *self,
                      cairo_t         *cr)

gsk/gskstroke.h

@@ -80,6 +80,10 @@ void                    gsk_stroke_set_dash_offset              (GskStroke
 GDK_AVAILABLE_IN_ALL
 float                   gsk_stroke_get_dash_offset              (const GskStroke        *self);
 
+GDK_AVAILABLE_IN_ALL
+void                    gsk_stroke_to_cairo                     (const GskStroke        *self,
+                                                                 cairo_t                *cr);
+
 
 
 G_END_DECLS

gsk/gskstrokeprivate.h

@@ -54,9 +54,6 @@ gsk_stroke_clear (GskStroke *stroke)
   stroke->n_dash = 0; /* better safe than sorry */
 }
 
-void                    gsk_stroke_to_cairo                     (const GskStroke        *self,
-                                                                 cairo_t                *cr);
-
 G_END_DECLS
 
 #endif /* __GSK_STROKE_PRIVATE_H__ */

tests/curve-editor.h

@@ -0,0 +1,38 @@
+#pragma once
+
+#include <gtk/gtk.h>
+
+G_BEGIN_DECLS
+
+#define CURVE_TYPE_EDITOR (curve_editor_get_type ())
+G_DECLARE_FINAL_TYPE (CurveEditor, curve_editor, CURVE, EDITOR, GtkWidget)
+
+GtkWidget * curve_editor_new      (void);
+
+void        curve_editor_set_edit (CurveEditor *self,
+                                   gboolean     edit);
+
+void        curve_editor_set_path (CurveEditor *self,
+                                   GskPath     *path);
+
+GskPath *   curve_editor_get_path (CurveEditor *self);
+
+void        curve_editor_set_stroke (CurveEditor *self,
+                                     GskStroke   *stroke);
+
+const GskStroke *
+            curve_editor_get_stroke (CurveEditor *self);
+
+
+void        curve_editor_set_color  (CurveEditor *self,
+                                     GdkRGBA     *color);
+
+const GdkRGBA *
+            curve_editor_get_color  (CurveEditor *self);
+
+gboolean    curve_editor_get_show_outline (CurveEditor *self);
+
+void        curve_editor_set_show_outline (CurveEditor *self,
+                                           gboolean     show_outline);
+
+G_END_DECLS

tests/curve.c

@@ -0,0 +1,217 @@
+#include <gtk/gtk.h>
+#include "curve-editor.h"
+
+
+static GskPath *
+make_circle_path (void)
+{
+  float w = 200;
+  float h = 200;
+  float cx = w / 2;
+  float cy = h / 2;
+  float pad = 20;
+  float r = (w - 2 * pad) / 2;
+  float k = 0.55228;
+  float kr = k  * r;
+  GskPathBuilder *builder;
+
+  builder = gsk_path_builder_new ();
+
+  gsk_path_builder_move_to (builder,  cx, pad);
+  gsk_path_builder_curve_to (builder, cx + kr, pad,
+                                      w - pad, cy - kr,
+                                      w - pad, cy);
+  gsk_path_builder_curve_to (builder, w - pad, cy + kr,
+                                      cx + kr, h - pad,
+                                      cx, h - pad);
+  gsk_path_builder_curve_to (builder, cx - kr, h - pad,
+                                      pad, cy + kr,
+                                      pad, cy);
+  gsk_path_builder_curve_to (builder, pad, cy - kr,
+                                      cx - kr, pad,
+                                      cx, pad);
+  gsk_path_builder_close (builder);
+
+  return gsk_path_builder_free_to_path (builder);
+}
+
+static void
+edit_changed (GtkToggleButton *button,
+              GParamSpec      *pspec,
+              CurveEditor     *editor)
+{
+  curve_editor_set_edit (editor, gtk_toggle_button_get_active (button));
+}
+
+static void
+reset (GtkButton   *button,
+       CurveEditor *editor)
+{
+  GskPath *path;
+
+  path = make_circle_path ();
+  curve_editor_set_path (editor, path);
+  gsk_path_unref (path);
+}
+
+static void
+line_width_changed (GtkSpinButton *spin,
+                    CurveEditor   *editor)
+{
+  GskStroke *stroke;
+
+  stroke = gsk_stroke_copy (curve_editor_get_stroke (editor));
+  gsk_stroke_set_line_width (stroke, gtk_spin_button_get_value (spin));
+  curve_editor_set_stroke (editor, stroke);
+  gsk_stroke_free (stroke);
+}
+
+static void
+cap_changed (GtkDropDown *combo,
+             GParamSpec  *pspec,
+             CurveEditor *editor)
+{
+  GskStroke *stroke;
+
+  stroke = gsk_stroke_copy (curve_editor_get_stroke (editor));
+  gsk_stroke_set_line_cap (stroke, (GskLineCap)gtk_drop_down_get_selected (combo));
+  curve_editor_set_stroke (editor, stroke);
+  gsk_stroke_free (stroke);
+}
+
+static void
+join_changed (GtkDropDown *combo,
+              GParamSpec  *pspec,
+              CurveEditor *editor)
+{
+  GskStroke *stroke;
+
+  stroke = gsk_stroke_copy (curve_editor_get_stroke (editor));
+  gsk_stroke_set_line_join (stroke, (GskLineJoin)gtk_drop_down_get_selected (combo));
+  curve_editor_set_stroke (editor, stroke);
+  gsk_stroke_free (stroke);
+}
+
+static void
+color_changed (GtkColorChooser *chooser,
+               CurveEditor     *editor)
+{
+  GdkRGBA color;
+
+  gtk_color_chooser_get_rgba (chooser, &color);
+  curve_editor_set_color (editor, &color);
+}
+
+static void
+stroke_toggled (GtkCheckButton *button,
+                CurveEditor    *editor)
+{
+  curve_editor_set_show_outline (editor, gtk_check_button_get_active (button));
+  gtk_widget_queue_draw (GTK_WIDGET (editor));
+}
+
+static void
+limit_changed (GtkSpinButton *spin,
+               CurveEditor   *editor)
+{
+  GskStroke *stroke;
+
+  stroke = gsk_stroke_copy (curve_editor_get_stroke (editor));
+  gsk_stroke_set_miter_limit (stroke, gtk_spin_button_get_value (spin));
+  curve_editor_set_stroke (editor, stroke);
+  gsk_stroke_free (stroke);
+}
+
+int
+main (int argc, char *argv[])
+{
+  GtkWindow *window;
+  GtkWidget *demo;
+  GtkWidget *edit_toggle;
+  GtkWidget *reset_button;
+  GtkWidget *titlebar;
+  GtkWidget *stroke_toggle;
+  GtkWidget *line_width_spin;
+  GtkWidget *stroke_button;
+  GtkWidget *popover;
+  GtkWidget *grid;
+  GtkWidget *cap_combo;
+  GtkWidget *join_combo;
+  GtkWidget *color_button;
+  GtkWidget *limit_spin;
+
+  gtk_init ();
+
+  window = GTK_WINDOW (gtk_window_new ());
+  gtk_window_set_default_size (GTK_WINDOW (window), 250, 250);
+
+  edit_toggle = gtk_toggle_button_new ();
+  gtk_button_set_icon_name (GTK_BUTTON (edit_toggle), "document-edit-symbolic");
+
+  reset_button = gtk_button_new_from_icon_name ("edit-undo-symbolic");
+
+  stroke_button = gtk_menu_button_new ();
+  gtk_menu_button_set_icon_name (GTK_MENU_BUTTON (stroke_button), "open-menu-symbolic");
+  popover = gtk_popover_new ();
+  gtk_menu_button_set_popover (GTK_MENU_BUTTON (stroke_button), popover);
+
+  grid = gtk_grid_new ();
+  gtk_grid_set_row_spacing (GTK_GRID (grid), 6);
+  gtk_grid_set_column_spacing (GTK_GRID (grid), 6);
+  gtk_popover_set_child (GTK_POPOVER (popover), grid);
+
+  gtk_grid_attach (GTK_GRID (grid), gtk_label_new ("Color:"), 0, 0, 1, 1);
+  color_button = gtk_color_button_new_with_rgba (&(GdkRGBA){ 0., 0., 0., 1.});
+  gtk_grid_attach (GTK_GRID (grid), color_button, 1, 0, 1, 1);
+
+  gtk_grid_attach (GTK_GRID (grid), gtk_label_new ("Line width:"), 0, 1, 1, 1);
+  line_width_spin = gtk_spin_button_new_with_range (1, 20, 1);
+  gtk_spin_button_set_value (GTK_SPIN_BUTTON (line_width_spin), 1);
+  gtk_grid_attach (GTK_GRID (grid), line_width_spin, 1, 1, 1, 1);
+
+  gtk_grid_attach (GTK_GRID (grid), gtk_label_new ("Line cap:"), 0, 2, 1, 1);
+  cap_combo = gtk_drop_down_new_from_strings ((const char *[]){"Butt", "Round", "Square", NULL});
+  gtk_grid_attach (GTK_GRID (grid), cap_combo, 1, 2, 1, 1);
+
+  gtk_grid_attach (GTK_GRID (grid), gtk_label_new ("Line join:"), 0, 3, 1, 1);
+  join_combo = gtk_drop_down_new_from_strings ((const char *[]){"Miter", "Miter-clip", "Round", "Bevel", NULL});
+  gtk_grid_attach (GTK_GRID (grid), join_combo, 1, 3, 1, 1);
+
+  gtk_grid_attach (GTK_GRID (grid), gtk_label_new ("Miter limit:"), 0, 4, 1, 1);
+  limit_spin = gtk_spin_button_new_with_range (0, 10, 1);
+  gtk_spin_button_set_digits (GTK_SPIN_BUTTON (limit_spin), 1);
+  gtk_spin_button_set_value (GTK_SPIN_BUTTON (limit_spin), 4);
+  gtk_grid_attach (GTK_GRID (grid), limit_spin, 1, 4, 1, 1);
+
+  stroke_toggle = gtk_check_button_new_with_label ("Show outline");
+  gtk_grid_attach (GTK_GRID (grid), stroke_toggle, 1, 5, 1, 1);
+
+  titlebar = gtk_header_bar_new ();
+  gtk_header_bar_pack_start (GTK_HEADER_BAR (titlebar), edit_toggle);
+  gtk_header_bar_pack_start (GTK_HEADER_BAR (titlebar), reset_button);
+  gtk_header_bar_pack_start (GTK_HEADER_BAR (titlebar), stroke_button);
+
+  gtk_window_set_titlebar (GTK_WINDOW (window), titlebar);
+
+  demo = curve_editor_new ();
+
+  g_signal_connect (stroke_toggle, "toggled", G_CALLBACK (stroke_toggled), demo);
+  g_signal_connect (edit_toggle, "notify::active", G_CALLBACK (edit_changed), demo);
+  g_signal_connect (reset_button, "clicked", G_CALLBACK (reset), demo);
+  g_signal_connect (cap_combo, "notify::selected", G_CALLBACK (cap_changed), demo);
+  g_signal_connect (join_combo, "notify::selected", G_CALLBACK (join_changed), demo);
+  g_signal_connect (color_button, "color-set", G_CALLBACK (color_changed), demo);
+  g_signal_connect (line_width_spin, "value-changed", G_CALLBACK (line_width_changed), demo);
+  g_signal_connect (limit_spin, "value-changed", G_CALLBACK (limit_changed), demo);
+
+  reset (NULL, CURVE_EDITOR (demo));
+
+  gtk_window_set_child (window, demo);
+
+  gtk_window_present (window);
+
+  while (g_list_model_get_n_items (gtk_window_get_toplevels ()) > 0)
+    g_main_context_iteration (NULL, TRUE);
+
+  return 0;
+}

tests/curve2.c

@@ -0,0 +1,815 @@
+#include <gtk/gtk.h>
+
+#define DEMO_TYPE_WIDGET (demo_widget_get_type ())
+G_DECLARE_FINAL_TYPE (DemoWidget, demo_widget, DEMO, WIDGET, GtkWidget)
+
+struct _DemoWidget
+{
+  GtkWidget parent_instance;
+  GskPath *orig_path;
+  GskPath *path;
+  GskPathMeasure *measure;
+  graphene_point_t point;
+  graphene_point_t point2;
+  graphene_vec2_t tangent;
+  double start, end;
+  float curvature;
+  graphene_point_t center;
+
+  gboolean track;
+  gboolean show_bounding_box;
+  GtkWidget *label;
+
+  gboolean do_stroke;
+  gboolean do_offset;
+  GskPath *stroke_path;
+  GskPathMeasure *stroke_measure;
+  GskStroke *stroke;
+  GskPath *outline_path;
+  GskStroke *outline_stroke;
+  gboolean inside;
+  GskFillRule fill_rule;
+  gboolean do_fill;
+
+  graphene_rect_t bounds;
+  gboolean show_cairo;
+
+  double zoom;
+};
+
+struct _DemoWidgetClass
+{
+  GtkWidgetClass parent_class;
+};
+
+G_DEFINE_TYPE (DemoWidget, demo_widget, GTK_TYPE_WIDGET)
+
+static void
+motion (GtkEventControllerMotion *controller,
+        double                    x,
+        double                    y,
+        DemoWidget               *self)
+{
+  if (self->track)
+    {
+      float distance;
+      char *text;
+      float t;
+
+      gsk_path_measure_get_closest_point_full (self->measure,
+                                               &GRAPHENE_POINT_INIT (x, y),
+                                               INFINITY,
+                                               &distance,
+                                               &self->point,
+                                               &t,
+                                               &self->tangent);
+
+      gsk_path_measure_get_point (self->measure, t, &self->point2, NULL);
+      self->curvature = gsk_path_measure_get_curvature (self->measure, t, &self->center);
+
+      text = g_strdup_printf ("%.1f", distance);
+      gtk_label_set_label (GTK_LABEL (self->label), text);
+
+      gtk_widget_queue_draw (GTK_WIDGET (self));
+    }
+
+  if (self->do_stroke && self->do_fill)
+    {
+      gboolean inside = TRUE;
+
+      inside = gsk_path_measure_in_fill (self->stroke_measure, &GRAPHENE_POINT_INIT (x, y), self->fill_rule);
+
+      if (self->inside != inside)
+        {
+          self->inside = inside;
+          gtk_widget_queue_draw (GTK_WIDGET (self));
+        }
+    }
+}
+
+static void
+demo_widget_init (DemoWidget *self)
+{
+  GtkEventController *controller;
+
+  self->start = 0;
+  self->end = 1;
+
+  self->label = gtk_label_new ("");
+  gtk_widget_set_parent (self->label, GTK_WIDGET (self));
+  gtk_widget_set_halign (self->label, GTK_ALIGN_END);
+  gtk_widget_set_valign (self->label, GTK_ALIGN_START);
+
+  controller = gtk_event_controller_motion_new ();
+  g_signal_connect (controller, "motion", G_CALLBACK (motion), self);
+  gtk_widget_add_controller (GTK_WIDGET (self), controller);
+}
+
+static void
+demo_widget_snapshot (GtkWidget   *widget,
+                      GtkSnapshot *snapshot)
+{
+  DemoWidget *self = DEMO_WIDGET (widget);
+  int width, height;
+  GskStroke *stroke;
+  GskPathBuilder *builder;
+  GskPath *path;
+  graphene_rect_t bounds;
+
+  if (!self->path)
+    return;
+
+  gtk_snapshot_save (snapshot);
+
+  gtk_snapshot_scale (snapshot, self->zoom, self->zoom);
+
+  width = gtk_widget_get_width (widget);
+  height = gtk_widget_get_width (widget);
+
+  if (self->do_stroke)
+    {
+      if (self->show_cairo)
+        {
+          cairo_t *cr;
+
+          graphene_rect_init (&bounds, 0, 0, width, height);
+          cr = gtk_snapshot_append_cairo (snapshot, &bounds);
+          gsk_path_to_cairo (self->path, cr);
+          gsk_stroke_to_cairo (self->stroke, cr);
+          cairo_set_source_rgba (cr, 0, 0, 1, 0.2);
+          cairo_stroke (cr);
+          cairo_destroy (cr);
+        }
+
+      if (self->do_fill && self->inside)
+        {
+           gtk_snapshot_push_fill (snapshot, self->stroke_path, self->fill_rule);
+
+           gtk_snapshot_append_color (snapshot,
+                                      &(GdkRGBA){ 1, 0, 1, 0.3},
+                                      &GRAPHENE_RECT_INIT (0, 0, width, height ));
+
+           gtk_snapshot_pop (snapshot);
+        }
+
+      gtk_snapshot_push_stroke (snapshot, self->outline_path, self->outline_stroke);
+
+      gtk_snapshot_append_color (snapshot,
+                                 &(GdkRGBA){ 0, 0, 0, 0.2},
+                                 &GRAPHENE_RECT_INIT (0, 0, width, height ));
+
+      gtk_snapshot_pop (snapshot);
+
+      stroke = gsk_stroke_new (1);
+      gtk_snapshot_push_stroke (snapshot, self->path, stroke);
+      gsk_stroke_free (stroke);
+
+      gtk_snapshot_append_color (snapshot,
+                                 &(GdkRGBA){ 0, 0, 0, 0.3},
+                                 &GRAPHENE_RECT_INIT (0, 0, width, height ));
+
+      gtk_snapshot_pop (snapshot);
+    }
+  else if (self->do_offset)
+    {
+      for (int i = -3; i < 4; i++)
+        {
+          path = gsk_path_offset (self->path,
+                                  5 * i,
+                                  gsk_stroke_get_line_join (self->stroke),
+                                  gsk_stroke_get_miter_limit (self->stroke));
+
+          gtk_snapshot_push_stroke (snapshot, path, self->outline_stroke);
+
+          gtk_snapshot_append_color (snapshot,
+                                     &(GdkRGBA){ 0, 0, 0, 1},
+                                     &GRAPHENE_RECT_INIT (0, 0, width, height ));
+
+          gtk_snapshot_pop (snapshot);
+          gsk_path_unref (path);
+        }
+    }
+  else
+    {
+      gtk_snapshot_push_stroke (snapshot, self->path, self->outline_stroke);
+
+      gtk_snapshot_append_color (snapshot,
+                                 &(GdkRGBA){ 0, 0, 0, 1},
+                                 &GRAPHENE_RECT_INIT (0, 0, width, height ));
+
+      gtk_snapshot_pop (snapshot);
+    }
+
+  if (self->show_bounding_box)
+    {
+      if (gsk_path_get_bounds (self->do_stroke ? self->outline_path : self->path, &bounds))
+        {
+          builder = gsk_path_builder_new ();
+
+          gsk_path_builder_add_rect (builder, &bounds);
+
+          path = gsk_path_builder_free_to_path (builder);
+
+          stroke = gsk_stroke_new (1.0);
+          gtk_snapshot_push_stroke (snapshot, path, stroke);
+          gsk_stroke_free (stroke);
+
+          gtk_snapshot_append_color (snapshot,
+                                     &(GdkRGBA){ 0, 0, 0, 0.5},
+                                     &GRAPHENE_RECT_INIT (0, 0, width, height ));
+
+          gtk_snapshot_pop (snapshot);
+
+          gsk_path_unref (path);
+        }
+    }
+
+  if (self->track)
+    {
+      graphene_point_t p;
+
+      p.x = self->point.x + graphene_vec2_get_x (&self->tangent) * 40;
+      p.y = self->point.y + graphene_vec2_get_y (&self->tangent) * 40;
+
+      builder = gsk_path_builder_new ();
+
+      gsk_path_builder_move_to (builder, self->point.x, self->point.y);
+      gsk_path_builder_line_to (builder, p.x, p.y);
+
+      path = gsk_path_builder_free_to_path (builder);
+
+      stroke = gsk_stroke_new (1.0);
+      gtk_snapshot_push_stroke (snapshot, path, stroke);
+      gsk_stroke_free (stroke);
+
+      gtk_snapshot_append_color (snapshot,
+                                 &(GdkRGBA){ 0, 0, 0, 1},
+                                 &GRAPHENE_RECT_INIT (0, 0, width, height ));
+
+      gtk_snapshot_pop (snapshot);
+
+      gsk_path_unref (path);
+
+      builder = gsk_path_builder_new ();
+
+      gsk_path_builder_add_circle (builder, &self->point, 5);
+      gsk_path_builder_add_circle (builder, &p, 2.5);
+      gsk_path_builder_add_circle (builder, &self->point2, 5);
+
+      path = gsk_path_builder_free_to_path (builder);
+
+      gtk_snapshot_push_fill (snapshot, path, 0);
+      gtk_snapshot_append_color (snapshot,
+                                 &(GdkRGBA){ 1, 0, 0, 1},
+                                 &GRAPHENE_RECT_INIT (0, 0, width, height ));
+      gtk_snapshot_pop (snapshot);
+
+      stroke = gsk_stroke_new (1.0);
+      gtk_snapshot_push_stroke (snapshot, path, stroke);
+      gsk_stroke_free (stroke);
+
+      gtk_snapshot_append_color (snapshot,
+                                 &(GdkRGBA){ 0, 0, 0, 1},
+                                 &GRAPHENE_RECT_INIT (0, 0, width, height ));
+
+      gtk_snapshot_pop (snapshot);
+
+      gsk_path_unref (path);
+
+      if (self->curvature != 0)
+        {
+          builder = gsk_path_builder_new ();
+          gsk_path_builder_add_circle (builder, &self->center, fabs (1/self->curvature));
+          gsk_path_builder_add_circle (builder, &self->center, 3);
+
+          path = gsk_path_builder_free_to_path (builder);
+
+          stroke = gsk_stroke_new (1.0);
+          gtk_snapshot_push_stroke (snapshot, path, stroke);
+          gsk_stroke_free (stroke);
+
+          gtk_snapshot_append_color (snapshot,
+                                     &(GdkRGBA){ 1, 0, 1, 1},
+                                     &GRAPHENE_RECT_INIT (0, 0, width, height ));
+
+          gtk_snapshot_pop (snapshot);
+        }
+
+      gtk_widget_snapshot_child (widget, self->label, snapshot);
+    }
+
+  gtk_snapshot_restore (snapshot);
+}
+
+static void
+demo_widget_measure (GtkWidget      *widget,
+                     GtkOrientation  orientation,
+                     int             for_size,
+                     int            *minimum,
+                     int            *natural,
+                     int            *minimum_baseline,
+                     int            *natural_baseline)
+{
+  DemoWidget *self = DEMO_WIDGET (widget);
+  float size;
+
+  if (orientation == GTK_ORIENTATION_HORIZONTAL)
+    size = self->zoom * (self->bounds.origin.x + self->bounds.size.width);
+  else
+    size = self->zoom * (self->bounds.origin.y + self->bounds.size.height);
+
+  *minimum = *natural = (int)size;
+}
+
+static void
+demo_widget_size_allocate (GtkWidget           *widget,
+                           int                  width,
+                           int                  height,
+                           int                  baseline)
+{
+  DemoWidget *self = DEMO_WIDGET (widget);
+  GtkRequisition min, nat;
+
+  gtk_widget_get_preferred_size (self->label, &min, &nat);
+
+  gtk_widget_size_allocate (self->label,
+                            &(GtkAllocation) { width - nat.width, 0, nat.width, nat.height},
+                            -1);
+}
+
+static void
+demo_widget_dispose (GObject *object)
+{
+  DemoWidget *self = DEMO_WIDGET (object);
+
+  g_clear_pointer (&self->path, gsk_path_unref);
+  g_clear_pointer (&self->measure, gsk_path_measure_unref);
+  g_clear_pointer (&self->stroke_path, gsk_path_unref);
+  g_clear_pointer (&self->stroke_measure, gsk_path_measure_unref);
+  g_clear_pointer (&self->stroke, gsk_stroke_free);
+  g_clear_pointer (&self->outline_path, gsk_path_unref);
+  g_clear_pointer (&self->outline_stroke, gsk_stroke_free);
+  g_clear_pointer (&self->label, gtk_widget_unparent);
+
+  G_OBJECT_CLASS (demo_widget_parent_class)->dispose (object);
+}
+
+static void
+demo_widget_class_init (DemoWidgetClass *class)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (class);
+  GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (class);
+
+  object_class->dispose = demo_widget_dispose;
+
+  widget_class->snapshot = demo_widget_snapshot;
+  widget_class->measure = demo_widget_measure;
+  widget_class->size_allocate = demo_widget_size_allocate;
+}
+
+static GtkWidget *
+demo_widget_new (void)
+{
+  return g_object_new (DEMO_TYPE_WIDGET, NULL);
+}
+
+static void
+update_outline_path (DemoWidget *self)
+{
+  if (self->stroke_path)
+    {
+      g_clear_pointer (&self->outline_path, gsk_path_unref);
+      self->outline_path = gsk_path_ref (self->stroke_path);
+      gtk_widget_queue_draw (GTK_WIDGET (self));
+    }
+}
+
+static void
+update_stroke_path (DemoWidget *self)
+{
+  g_clear_pointer (&self->stroke_path, gsk_path_unref);
+  g_clear_pointer (&self->stroke_measure, gsk_path_measure_unref);
+
+  if (self->do_stroke)
+    {
+      self->stroke_path = gsk_path_stroke (self->path, self->stroke);
+      self->stroke_measure = gsk_path_measure_new (self->stroke_path);
+      update_outline_path (self);
+    }
+
+  gsk_path_get_bounds (self->orig_path, &self->bounds);
+
+  if (self->stroke_path)
+    {
+      graphene_rect_t b;
+      gsk_path_get_bounds (self->stroke_path, &b);
+      graphene_rect_union (&b, &self->bounds, &self->bounds);
+    }
+
+  gtk_widget_queue_resize (GTK_WIDGET (self));
+}
+
+static void
+update_path (DemoWidget *self)
+{
+  g_clear_pointer (&self->path, gsk_path_unref);
+  g_clear_pointer (&self->measure, gsk_path_measure_unref);
+
+  if (self->start > 0 || self->end < 1)
+    {
+      GskPathMeasure *measure;
+      GskPathBuilder *builder;
+      float length;
+
+      measure = gsk_path_measure_new (self->orig_path);
+      length = gsk_path_measure_get_length (measure);
+      builder = gsk_path_builder_new ();
+      gsk_path_builder_add_segment (builder, measure, self->start * length, self->end * length);
+      self->path = gsk_path_builder_free_to_path (builder);
+      gsk_path_measure_unref (measure);
+    }
+  else
+    self->path = gsk_path_ref (self->orig_path);
+
+  self->measure = gsk_path_measure_new (self->path);
+
+  update_stroke_path (self);
+}
+
+static void
+demo_widget_set_path (DemoWidget *self,
+                      GskPath    *path)
+{
+  g_clear_pointer (&self->orig_path, gsk_path_unref);
+  self->orig_path = gsk_path_ref (path);
+
+  update_path (self);
+}
+
+static void
+activate (GtkEntry *entry,
+          DemoWidget *demo)
+{
+  GskPath *path;
+
+  path = gsk_path_parse (gtk_editable_get_text (GTK_EDITABLE (entry)));
+  if (path)
+    {
+      demo_widget_set_path (demo, path);
+      gsk_path_unref (path);
+    }
+}
+
+static void
+init_demo (DemoWidget  *demo,
+           GtkEditable *editable)
+{
+  GskPathBuilder *builder;
+  GskPath *path;
+  char *string;
+
+  builder = gsk_path_builder_new ();
+  gsk_path_builder_add_circle (builder, &GRAPHENE_POINT_INIT (150, 150), 100);
+  gsk_path_builder_add_rect (builder, &GRAPHENE_RECT_INIT (100, 100, 100, 100));
+  gsk_path_builder_move_to (builder, 300, 150);
+  gsk_path_builder_curve_to (builder, 300, 50, 400, 50, 400, 150);
+  gsk_path_builder_curve_to (builder, 400, 250, 500, 250, 500, 150);
+  gsk_path_builder_line_to (builder, 600, 150);
+  gsk_path_builder_line_to (builder, 530, 190);
+  path = gsk_path_builder_free_to_path (builder);
+
+  demo_widget_set_path (demo, path);
+
+  string = gsk_path_to_string (path);
+  gtk_editable_set_text (editable, string);
+  g_free (string);
+  gsk_path_unref (path);
+
+  demo->stroke = gsk_stroke_new (20);
+  demo->outline_stroke = gsk_stroke_new (1);
+
+  demo->zoom = 1;
+}
+
+static void
+zoom_changed (GtkRange   *range,
+              DemoWidget *self)
+{
+  self->zoom = gtk_range_get_value (range);
+  gtk_widget_queue_resize (GTK_WIDGET (self));
+}
+
+static void
+track_toggled (GtkCheckButton *button,
+               DemoWidget      *self)
+{
+  self->track = gtk_check_button_get_active (button);
+  gtk_widget_queue_draw (GTK_WIDGET (self));
+}
+
+static void
+bb_toggled (GtkCheckButton *button,
+            DemoWidget      *self)
+{
+  self->show_bounding_box = gtk_check_button_get_active (button);
+  gtk_widget_queue_draw (GTK_WIDGET (self));
+}
+
+static void
+cairo_toggled (GtkCheckButton *button,
+               DemoWidget      *self)
+{
+  self->show_cairo = gtk_check_button_get_active (button);
+  gtk_widget_queue_draw (GTK_WIDGET (self));
+}
+
+static void
+stroke_toggled (GtkCheckButton *button,
+                DemoWidget      *self)
+{
+  self->do_stroke = gtk_check_button_get_active (button);
+  update_stroke_path (self);
+  gtk_widget_queue_draw (GTK_WIDGET (self));
+}
+
+static void
+offset_toggled (GtkCheckButton *button,
+                DemoWidget      *self)
+{
+  self->do_offset = gtk_check_button_get_active (button);
+  gtk_widget_queue_draw (GTK_WIDGET (self));
+}
+
+static void
+fill_toggled (GtkCheckButton *button,
+              DemoWidget      *self)
+{
+  self->do_fill = gtk_check_button_get_active (button);
+  gtk_widget_queue_draw (GTK_WIDGET (self));
+}
+
+static GtkWidget *start_scale;
+static GtkWidget *end_scale;
+
+static void
+range_changed (GtkRange   *range,
+               DemoWidget *self)
+{
+  double start, end;
+
+  if (range == GTK_RANGE (start_scale))
+    {
+      start = gtk_range_get_value (range);
+      end = MAX (start, gtk_range_get_value (GTK_RANGE (end_scale)));
+      gtk_range_set_value (GTK_RANGE (end_scale), end);
+    }
+  else
+    {
+      end = gtk_range_get_value (range);
+      start = MIN (end, gtk_range_get_value (GTK_RANGE (start_scale)));
+      gtk_range_set_value (GTK_RANGE (start_scale), start);
+    }
+
+  self->start = start;
+  self->end = end;
+
+  update_path (self);
+}
+
+static void
+fill_rule_changed (GtkDropDown *combo,
+                   GParamSpec  *pspec,
+                   DemoWidget  *self)
+{
+  self->fill_rule = (GskFillRule)gtk_drop_down_get_selected (combo);
+  gtk_widget_queue_draw (GTK_WIDGET (self));
+}
+
+static void
+cap_changed (GtkDropDown *combo,
+             GParamSpec  *pspec,
+             DemoWidget  *self)
+{
+  gsk_stroke_set_line_cap (self->stroke, (GskLineCap)gtk_drop_down_get_selected (combo));
+  update_stroke_path (self);
+}
+
+static void
+join_changed (GtkDropDown *combo,
+              GParamSpec  *pspec,
+              DemoWidget  *self)
+{
+  gsk_stroke_set_line_join (self->stroke, (GskLineJoin)gtk_drop_down_get_selected (combo));
+  update_stroke_path (self);
+}
+
+static void
+limit_changed (GtkSpinButton *spin,
+               DemoWidget    *self)
+{
+  gsk_stroke_set_miter_limit (self->stroke, gtk_spin_button_get_value (spin));
+  update_stroke_path (self);
+}
+
+static void
+stroke_width_changed (GtkSpinButton *spin,
+                      DemoWidget    *self)
+{
+  gsk_stroke_set_line_width (self->stroke, gtk_spin_button_get_value (spin));
+  update_stroke_path (self);
+}
+
+static void
+line_width_changed (GtkSpinButton *spin,
+                    DemoWidget    *self)
+{
+  gsk_stroke_set_line_width (self->outline_stroke, gtk_spin_button_get_value (spin));
+  update_outline_path (self);
+}
+
+static void
+dash_changed (GtkEntry   *entry,
+              DemoWidget *self)
+{
+  const char *text;
+  char **s;
+  float dash[20];
+  int i;
+
+  text = gtk_editable_get_text (GTK_EDITABLE (entry));
+  s = g_strsplit (text, " ", -1);
+  for (i = 0; s[i]; i++)
+    {
+      char *end;
+      float f;
+
+      f = g_strtod (s[i], &end);
+      if (*end != '\0')
+        return;
+
+      dash[i] = f;
+    }
+
+  g_strfreev (s);
+
+  gsk_stroke_set_dash (self->stroke, dash, i);
+
+  update_stroke_path (self);
+}
+
+static void
+dash_offset_changed (GtkSpinButton *spin,
+                     DemoWidget    *self)
+{
+  gsk_stroke_set_dash_offset (self->stroke, gtk_spin_button_get_value (spin));
+  update_stroke_path (self);
+}
+
+int
+main (int argc, char *argv[])
+{
+  GtkWidget *window, *box, *demo, *entry;
+  GtkWidget *popover, *button, *grid;
+  GtkWidget *header, *toggle, *toggle2, *toggle3;
+  GtkWidget *combo, *spin, *sw, *hbox;
+  GtkWidget *zoom_scale;
+  int row;
+
+  gtk_init ();
+
+  window = gtk_window_new ();
+  gtk_window_set_default_size (GTK_WINDOW (window), 700, 500);
+  box = gtk_box_new (GTK_ORIENTATION_VERTICAL, 0);
+  gtk_window_set_child (GTK_WINDOW (window), box);
+
+  demo = demo_widget_new ();
+  gtk_widget_set_hexpand (demo, TRUE);
+  gtk_widget_set_vexpand (demo, TRUE);
+  sw = gtk_scrolled_window_new ();
+  gtk_box_append (GTK_BOX (box), sw);
+  gtk_scrolled_window_set_child (GTK_SCROLLED_WINDOW (sw), demo);
+
+  header = gtk_header_bar_new ();
+  button = gtk_menu_button_new ();
+  gtk_menu_button_set_icon_name (GTK_MENU_BUTTON (button), "emblem-system-symbolic");
+  gtk_header_bar_pack_start (GTK_HEADER_BAR (header), button);
+
+  zoom_scale = gtk_scale_new_with_range (GTK_ORIENTATION_HORIZONTAL, 1, 20, 0.25);
+  gtk_range_set_value (GTK_RANGE (zoom_scale), 1);
+  g_signal_connect (zoom_scale, "value-changed", G_CALLBACK (zoom_changed), demo);
+  gtk_widget_set_size_request (zoom_scale, 150, -1);
+  gtk_header_bar_pack_end (GTK_HEADER_BAR (header), zoom_scale);
+
+  gtk_window_set_titlebar (GTK_WINDOW (window), header);
+
+  popover = gtk_popover_new ();
+  gtk_menu_button_set_popover (GTK_MENU_BUTTON (button), popover);
+
+  grid = gtk_grid_new ();
+  gtk_grid_set_row_spacing (GTK_GRID (grid), 6);
+  gtk_grid_set_column_spacing (GTK_GRID (grid), 6);
+  gtk_popover_set_child (GTK_POPOVER (popover), grid);
+
+  row = 0;
+  hbox = gtk_box_new (GTK_ORIENTATION_HORIZONTAL, 6);
+  toggle = gtk_check_button_new_with_label ("Plain");
+  gtk_check_button_set_active (GTK_CHECK_BUTTON (toggle), TRUE);
+  gtk_box_append (GTK_BOX (hbox), toggle);
+  gtk_widget_set_hexpand (toggle, TRUE);
+  toggle2 = gtk_check_button_new_with_label ("Stroke");
+  gtk_widget_set_hexpand (toggle2, TRUE);
+  gtk_box_append (GTK_BOX (hbox), toggle2);
+  gtk_check_button_set_group (GTK_CHECK_BUTTON (toggle2), GTK_CHECK_BUTTON (toggle));
+  g_signal_connect (toggle2, "toggled", G_CALLBACK (stroke_toggled), demo);
+  toggle3 = gtk_check_button_new_with_label ("Offset");
+  gtk_widget_set_hexpand (toggle3, TRUE);
+  gtk_box_append (GTK_BOX (hbox), toggle3);
+  gtk_check_button_set_group (GTK_CHECK_BUTTON (toggle3), GTK_CHECK_BUTTON (toggle));
+  g_signal_connect (toggle3, "toggled", G_CALLBACK (offset_toggled), demo);
+  gtk_grid_attach (GTK_GRID (grid), hbox, 0, row++, 2, 1);
+
+  gtk_grid_attach (GTK_GRID (grid), gtk_label_new ("Fill rule"), 0, row, 1, 1);
+
+  combo = gtk_drop_down_new_from_strings ((const char *[]){"Winding", "Even-Odd", NULL });
+  g_signal_connect (combo, "notify::selected", G_CALLBACK (fill_rule_changed), demo);
+  gtk_grid_attach (GTK_GRID (grid), combo, 1, row++, 1, 1);
+
+  gtk_grid_attach (GTK_GRID (grid), gtk_label_new ("Line cap:"), 0, row, 1, 1);
+  combo = gtk_drop_down_new_from_strings ((const char *[]){"Butt", "Round", "Square", NULL});
+  g_signal_connect (combo, "notify::selected", G_CALLBACK (cap_changed), demo);
+  gtk_grid_attach (GTK_GRID (grid), combo, 1, row++, 1, 1);
+
+  gtk_grid_attach (GTK_GRID (grid), gtk_label_new ("Line join:"), 0, row, 1, 1);
+  combo = gtk_drop_down_new_from_strings ((const char *[]){"Miter", "Miter-clip", "Round", "Bevel", "Arcs", NULL});
+  g_signal_connect (combo, "notify::selected", G_CALLBACK (join_changed), demo);
+  gtk_grid_attach (GTK_GRID (grid), combo, 1, row++, 1, 1);
+
+  gtk_grid_attach (GTK_GRID (grid), gtk_label_new ("Miter limit:"), 0, row, 1, 1);
+  spin = gtk_spin_button_new_with_range (0, 10, 1);
+  gtk_spin_button_set_digits (GTK_SPIN_BUTTON (spin), 1);
+  gtk_spin_button_set_value (GTK_SPIN_BUTTON (spin), 4);
+  g_signal_connect (spin, "value-changed", G_CALLBACK (limit_changed), demo);
+  gtk_grid_attach (GTK_GRID (grid), spin, 1, row++, 1, 1);
+
+  gtk_grid_attach (GTK_GRID (grid), gtk_label_new ("Stroke width:"), 0, row, 1, 1);
+  spin = gtk_spin_button_new_with_range (1, 40, 1);
+  gtk_spin_button_set_value (GTK_SPIN_BUTTON (spin), 20);
+  g_signal_connect (spin, "value-changed", G_CALLBACK (stroke_width_changed), demo);
+  gtk_grid_attach (GTK_GRID (grid), spin, 1, row++, 1, 1);
+
+  gtk_grid_attach (GTK_GRID (grid), gtk_label_new ("Line width:"), 0, row, 1, 1);
+  spin = gtk_spin_button_new_with_range (1, 20, 1);
+  gtk_spin_button_set_value (GTK_SPIN_BUTTON (spin), 1);
+  g_signal_connect (spin, "value-changed", G_CALLBACK (line_width_changed), demo);
+  gtk_grid_attach (GTK_GRID (grid), spin, 1, row++, 1, 1);
+
+  gtk_grid_attach (GTK_GRID (grid), gtk_label_new ("Dash pattern:"), 0, row, 1, 1);
+  entry = gtk_entry_new ();
+  g_signal_connect (entry, "changed", G_CALLBACK (dash_changed), demo);
+  gtk_grid_attach (GTK_GRID (grid), entry, 1, row++, 1, 1);
+
+  gtk_grid_attach (GTK_GRID (grid), gtk_label_new ("Dash offset:"), 0, row, 1, 1);
+  spin = gtk_spin_button_new_with_range (-1000, 1000, 10);
+  gtk_spin_button_set_digits (GTK_SPIN_BUTTON (spin), 1);
+  gtk_spin_button_set_value (GTK_SPIN_BUTTON (spin), 0);
+  g_signal_connect (spin, "value-changed", G_CALLBACK (dash_offset_changed), demo);
+  gtk_grid_attach (GTK_GRID (grid), spin, 1, row++, 1, 1);
+
+  toggle = gtk_check_button_new_with_label ("Show closest point");
+  g_signal_connect (toggle, "toggled", G_CALLBACK (track_toggled), demo);
+  gtk_grid_attach (GTK_GRID (grid), toggle, 1, row++, 1, 1);
+
+  toggle = gtk_check_button_new_with_label ("Show bounding box");
+  g_signal_connect (toggle, "toggled", G_CALLBACK (bb_toggled), demo);
+  gtk_grid_attach (GTK_GRID (grid), toggle, 1, row++, 1, 1);
+
+  toggle = gtk_check_button_new_with_label ("Highlight on hover");
+  g_signal_connect (toggle, "toggled", G_CALLBACK (fill_toggled), demo);
+  gtk_grid_attach (GTK_GRID (grid), toggle, 1, row++, 1, 1);
+
+  toggle = gtk_check_button_new_with_label ("Compare cairo stroke");
+  g_signal_connect (toggle, "toggled", G_CALLBACK (cairo_toggled), demo);
+  gtk_grid_attach (GTK_GRID (grid), toggle, 1, row++, 1, 1);
+
+  entry = gtk_entry_new ();
+  g_signal_connect (entry, "activate", G_CALLBACK (activate), demo);
+  gtk_box_append (GTK_BOX (box), entry);
+
+  start_scale = gtk_scale_new_with_range (GTK_ORIENTATION_HORIZONTAL, 0, 1, 0.01);
+  g_signal_connect (start_scale, "value-changed", G_CALLBACK (range_changed), demo);
+  gtk_box_append (GTK_BOX (box), start_scale);
+
+  end_scale = gtk_scale_new_with_range (GTK_ORIENTATION_HORIZONTAL, 0, 1, 0.01);
+  gtk_range_set_value (GTK_RANGE (end_scale), 1);
+  g_signal_connect (end_scale, "value-changed", G_CALLBACK (range_changed), demo);
+  gtk_box_append (GTK_BOX (box), end_scale);
+
+  init_demo (DEMO_WIDGET (demo), GTK_EDITABLE (entry));
+
+  gtk_window_present (GTK_WINDOW (window));
+
+  while (g_list_model_get_n_items (gtk_window_get_toplevels ()) > 0)
+    g_main_context_iteration (NULL, TRUE);
+
+  return 0;
+}

tests/meson.build

@@ -5,6 +5,8 @@ gtk_tests = [
   ['blur-performance', ['../gsk/gskcairoblur.c']],
   ['motion-compression'],
   ['overlayscroll'],
+  ['curve', ['curve.c', 'curve-editor.c']],
+  ['curve2'],
   ['testupload'],
   ['testtransform'],
   ['testdropdown'],