[gdk] Add gdk_window_has_native() function

https://bugzilla.gnome.org/show_bug.cgi?id=622677

docs/reference/gdk/gdk-sections.txt

@@ -674,6 +674,7 @@ gdk_window_move_resize
 gdk_window_scroll
 gdk_window_move_region
 gdk_window_flush
+gdk_window_has_native
 gdk_window_ensure_native
 gdk_window_reparent
 gdk_window_clear

gdk/gdk.symbols

@@ -727,6 +727,7 @@ gdk_window_get_toplevels
 gdk_window_get_update_area
 gdk_window_get_user_data
 gdk_window_get_window_type
+gdk_window_has_native
 gdk_window_invalidate_maybe_recurse
 gdk_window_invalidate_rect
 gdk_window_invalidate_region

gdk/gdkwindow.c

@@ -2261,6 +2261,29 @@ from_embedder (GdkWindowObject *window,
                  offscreen_x, offscreen_y);
 }
 
+/**
+ * gdk_window_has_native:
+ * @window: a #GdkWindow
+ *
+ * Checks whether the window has a native window or not. Note that
+ * you can use gdk_window_ensure_native() if a native window is needed.
+ *
+ * Returns: %TRUE if the %window has a native window, %FALSE otherwise.
+ *
+ * Since: 2.22
+ */
+gboolean
+gdk_window_has_native (GdkWindow *window)
+{
+  GdkWindowObject *w;
+
+  g_return_val_if_fail (GDK_IS_WINDOW (window), FALSE);
+
+  w = GDK_WINDOW_OBJECT (window);
+
+  return w->parent == NULL || w->parent->impl != w->impl;
+}
+
 /**
  * gdk_window_get_position:
  * @window: a #GdkWindow

gdk/gdkwindow.h

@@ -480,6 +480,7 @@ GdkWindow*    gdk_window_lookup_for_display (GdkDisplay      *display,
 
 /* GdkWindow */
 
+gboolean      gdk_window_has_native      (GdkWindow       *window);
 #ifndef GDK_DISABLE_DEPRECATED
 void	      gdk_window_set_hints	 (GdkWindow	  *window,
 					  gint		   x,