Add a "devel" CSS theme for our demos

It's useful to know if you're running the demos from an unstable version
of GTK+, so we should use a CSS fragment that updates the visual
identity of gtk-demo and gtk-widget-factory depending on the version of
GTK+ they are running against.

demos/gtk-demo/demo.gresource.xml

@@ -3,6 +3,7 @@
   <gresource prefix="/ui">
     <file preprocess="xml-stripblanks">main.ui</file>
     <file preprocess="xml-stripblanks">appmenu.ui</file>
+    <file>theme.css</file>
   </gresource>
   <gresource prefix="/application_demo">
     <file>application.c</file>

demos/gtk-demo/main.c

@@ -997,6 +997,41 @@ scrollbar_popup (GtkWidget *scrollbar, GtkWidget *menu)
   return TRUE;
 }
 
+static void
+settings__notify_gtk_theme_name (GObject *gobject,
+                                 GParamSpec *pspec,
+                                 gpointer data)
+{
+  static GtkCssProvider *css_provider;
+
+  GtkWidget *window = data;
+  char *theme_name;
+
+  g_object_get (gobject, "gtk-theme-name", &theme_name, NULL);
+  if (g_strcmp0 (theme_name, "Adwaita") == 0)
+    {
+      if (css_provider == NULL)
+        {
+          css_provider = gtk_css_provider_new ();
+          gtk_css_provider_load_from_resource (css_provider, "/ui/theme.css");
+          gtk_style_context_add_provider_for_display (gtk_widget_get_display (window),
+                                                      GTK_STYLE_PROVIDER (css_provider),
+                                                      GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);
+        }
+    }
+  else
+    {
+      if (css_provider != NULL)
+        {
+          gtk_style_context_remove_provider_for_display (gtk_widget_get_display (window),
+                                                         GTK_STYLE_PROVIDER (css_provider));
+          g_clear_object (&css_provider);
+        }
+    }
+
+  g_free (theme_name);
+}
+
 static void
 activate (GApplication *app)
 {
@@ -1029,6 +1064,20 @@ activate (GApplication *app)
                                    win_entries, G_N_ELEMENTS (win_entries),
                                    window);
 
+  g_signal_connect (gtk_settings_get_default (), "notify::gtk-theme-name",
+                    G_CALLBACK (settings__notify_gtk_theme_name),
+                    window);
+
+  if (gtk_get_minor_version () % 2 != 0)
+    {
+      GtkStyleContext *context = gtk_widget_get_style_context (GTK_WIDGET (window));
+      gtk_style_context_add_class (context, "devel");
+    }
+
+  settings__notify_gtk_theme_name (G_OBJECT (gtk_widget_get_settings (GTK_WIDGET (window))),
+                                   NULL,
+                                   window);
+
   notebook = (GtkWidget *)gtk_builder_get_object (builder, "notebook");
 
   info_view = (GtkWidget *)gtk_builder_get_object (builder, "info-textview");

demos/gtk-demo/theme.css

@@ -0,0 +1,10 @@
+window.devel headerbar {
+    background: #cbd2d9 -gtk-icontheme("system-run-symbolic") 70% 0/64px 64px no-repeat, linear-gradient(to left, #a5b1bd 0%, #a5b1bd 8%, @theme_bg_color 25%);
+    box-shadow: inset 0 1px #f1f3f5;
+    border-color: #909fae;
+    color: rgba(46, 52, 54, 0.2);
+}
+
+window.devel headerbar label {
+    color: @theme_fg_color;
+}

demos/widget-factory/widget-factory.c

@@ -1605,6 +1605,27 @@ adjustment3_value_changed (GtkAdjustment *adj, GtkProgressBar *pbar)
   gtk_progress_bar_set_fraction (pbar, fraction);
 }
 
+static void
+settings__notify_gtk_theme_name (GObject *gobject,
+                                 GParamSpec *pspec,
+                                 gpointer data)
+{
+  GtkWidget *window = data;
+  char *theme_name = NULL;
+
+  g_object_get (gobject, "gtk-theme-name", &theme_name, NULL);
+
+  if (g_strcmp0 (theme_name, "Adwaita") == 0)
+    {
+      if (gtk_get_minor_version () % 2 != 0)
+        gtk_style_context_add_class (gtk_widget_get_style_context (window), "devel");
+    }
+  else
+    gtk_style_context_remove_class (gtk_widget_get_style_context (window), "devel");
+
+  g_free (theme_name);
+}
+
 static void
 activate (GApplication *app)
 {
@@ -1680,6 +1701,13 @@ activate (GApplication *app)
                                    win_entries, G_N_ELEMENTS (win_entries),
                                    window);
 
+  g_signal_connect (gtk_settings_get_default (), "notify::gtk-theme-name",
+                    G_CALLBACK (settings__notify_gtk_theme_name),
+                    window);
+  settings__notify_gtk_theme_name (G_OBJECT (gtk_settings_get_default ()),
+                                   NULL,
+                                   window);
+
   for (i = 0; i < G_N_ELEMENTS (accels); i++)
     gtk_application_set_accels_for_action (GTK_APPLICATION (app), accels[i].action_and_target, accels[i].accelerators);
 

demos/widget-factory/widget-factory.css

@@ -24,3 +24,14 @@
 .border-ridge {
   border-width: 2px;
 }
+
+window.devel headerbar {
+    background: #cbd2d9 -gtk-icontheme("system-run-symbolic") 70% 0/64px 64px no-repeat, linear-gradient(to left, #a5b1bd 0%, #a5b1bd 8%, @theme_bg_color 25%);
+    box-shadow: inset 0 1px #f1f3f5;
+    border-color: #909fae;
+    color: rgba(46, 52, 54, 0.2);
+}
+
+window.devel headerbar label {
+    color: @theme_fg_color;
+}