Add gdk_window_set_update_handler

This lets you register callbacks for when child widgets invalidate
areas of the window read it and/or change it.

For instance, this lets you do rendering effects and keeping offscreen
caches uptodate.

gdk/gdkinternals.h

@@ -266,6 +266,7 @@ struct _GdkWindow
   guint num_offscreen_children;
 
   GdkFrameClock *frame_clock; /* NULL to use from parent or default */
+  GdkWindowUpdateHandlerFunc update_handler;
 };
 
 #define GDK_WINDOW_TYPE(d) (((GDK_WINDOW (d)))->window_type)

gdk/gdkwindow.c

@@ -3662,6 +3662,13 @@ gdk_window_invalidate_rect (GdkWindow          *window,
   gdk_window_invalidate_rect_full (window, rect, invalidate_children);
 }
 
+void
+gdk_window_set_update_handler (GdkWindow *window,
+			       GdkWindowUpdateHandlerFunc handler)
+{
+  window->update_handler = handler;
+}
+
 static void
 draw_ugly_color (GdkWindow       *window,
 		 const cairo_region_t *region)
@@ -3749,8 +3756,8 @@ gdk_window_invalidate_maybe_recurse_full (GdkWindow            *window,
                                           GdkWindowChildFunc    child_func,
 					  gpointer              user_data)
 {
-  GdkWindow *impl_window;
   cairo_region_t *visible_region;
+  cairo_rectangle_int_t r;
 
   g_return_if_fail (GDK_IS_WINDOW (window));
 
@@ -3763,26 +3770,41 @@ gdk_window_invalidate_maybe_recurse_full (GdkWindow            *window,
       window->window_type == GDK_WINDOW_ROOT)
     return;
 
-  visible_region = gdk_window_get_visible_region (window);
+  r.x = 0;
-  cairo_region_intersect (visible_region, region);
+  r.y = 0;
+  r.width = window->width;
+  r.height = window->height;
+
+  visible_region = cairo_region_copy (region);
+  cairo_region_intersect_rectangle (visible_region, &r);
 
   invalidate_impl_subwindows (window, region, child_func, user_data, 0, 0);
 
-  impl_window = gdk_window_get_impl_window (window);
+  if (debug_updates)
+    draw_ugly_color (window, visible_region);
 
-  if (!cairo_region_is_empty (visible_region))
+  while (window != NULL && 
+	 !cairo_region_is_empty (visible_region))
     {
-      if (debug_updates)
+      if (gdk_window_has_impl (window))
-	draw_ugly_color (window, visible_region);
+	{
-
+	  impl_window_add_update_area (window, visible_region);
-      /* Convert to impl coords */
+	  break;
-      cairo_region_translate (visible_region, window->abs_x, window->abs_y);
+	}
-
+      else
-      /* Only invalidate area if app requested expose events or if
+	{
-	 we need to clear the area (by request or to emulate background
+	  if (window->update_handler)
-	 clearing for non-native windows or native windows with no support
+	    {
-	 for window backgrounds */
+	      if (!window->update_handler (window, visible_region))
-      impl_window_add_update_area (impl_window, visible_region);
+		break;
+	    }
+	  cairo_region_translate (visible_region,
+				  window->x, window->y);
+	  window = window->parent;
+	  r.width = window->width;
+	  r.height = window->height;
+	  cairo_region_intersect_rectangle (visible_region, &r);
+	}
     }
 
   cairo_region_destroy (visible_region);

gdk/gdkwindow.h

@@ -633,6 +633,10 @@ gboolean gdk_window_set_static_gravities (GdkWindow *window,
                                           gboolean   use_static);
 
 /* GdkWindow */
+typedef gboolean (*GdkWindowUpdateHandlerFunc)  (GdkWindow *window,
+						 cairo_region_t *region);
+void gdk_window_set_update_handler (GdkWindow *window,
+				    GdkWindowUpdateHandlerFunc handler);
 
 gboolean      gdk_window_has_native         (GdkWindow       *window);
 void              gdk_window_set_type_hint (GdkWindow        *window,