Introduce API to get the preferred visual

Unless GDK_RGBA=0 is set, this will be the RGBA visual.
The new function is called gdk_screen_get_preferred_visual().

https://bugzilla.gnome.org/show_bug.cgi?id=630217

3 files changed, 33 insertions, 0 deletions

diff --git a/gdk/gdkscreen.c b/gdk/gdkscreen.c
index 743b850bd5..113d2a4052 100644
--- a/gdk/gdkscreen.c
+++ b/gdk/gdkscreen.c
@@ -913,6 +913,36 @@ gdk_screen_get_rgba_visual (GdkScreen *screen)
 }
 
 /**
+ * gdk_screen_get_preferred_visual:
+ * @screen: a #GdkScreen
+ *
+ * Returns the visual that is preferred when creating windows.
+ *
+ * This will be the visual returned by gdk_screen_get_rgba_visual()
+ * unless that is not available, or unless the environment
+ * variable <envar>GDK_RGBA</envar> is set to 0.
+ *
+ * Return value: (transfer none): the preferred visual to use
+ *     for windows
+ *
+ * Since: 3.12
+ */
+GdkVisual *
+gdk_screen_get_preferred_visual (GdkScreen *screen)
+{
+  GdkVisual *visual;
+
+  g_return_val_if_fail (GDK_IS_SCREEN (screen), NULL);
+
+  visual = gdk_screen_get_rgba_visual (screen);
+
+  if (visual == NULL || g_strcmp0 (g_getenv ("GDK_RGBA"), "0") == 0)
+    visual = gdk_screen_get_system_visual (screen);
+
+  return visual;
+}
+
+/**
  * gdk_screen_is_composited:
  * @screen: a #GdkScreen
  *
diff --git a/gdk/gdkscreen.h b/gdk/gdkscreen.h
index dde5524fa4..57d613245b 100644
--- a/gdk/gdkscreen.h
+++ b/gdk/gdkscreen.h
@@ -45,6 +45,8 @@ GDK_AVAILABLE_IN_ALL
 GdkVisual *  gdk_screen_get_system_visual     (GdkScreen   *screen);
 GDK_AVAILABLE_IN_ALL
 GdkVisual *  gdk_screen_get_rgba_visual       (GdkScreen   *screen);
+GDK_AVAILABLE_IN_3_12
+GdkVisual *  gdk_screen_get_preferred_visual  (GdkScreen   *screen);
 GDK_AVAILABLE_IN_ALL
 gboolean     gdk_screen_is_composited         (GdkScreen   *screen);
 
diff --git a/gdk/gdkscreenprivate.h b/gdk/gdkscreenprivate.h
index 23cf1bdae2..b73a0926f0 100644
--- a/gdk/gdkscreenprivate.h
+++ b/gdk/gdkscreenprivate.h
@@ -66,6 +66,7 @@ struct _GdkScreenClass
   GList *      (* list_visuals)          (GdkScreen *screen);
   GdkVisual *  (* get_system_visual)     (GdkScreen *screen);
   GdkVisual *  (* get_rgba_visual)       (GdkScreen *screen);
+  GdkVisual *  (* get_preferred_visual)  (GdkScreen *screen);
   gboolean     (* is_composited)         (GdkScreen *screen);
   gchar *      (* make_display_name)     (GdkScreen *screen);
   GdkWindow *  (* get_active_window)     (GdkScreen *screen);