GdkWindowX11: Only start a frame when we emit damage

Instead of communicating the start of a frame to the window manager
as soon as we begin a frame, start a frame only when we know we've
actually created damage to the contents of a window.

(This uses cairo_set_mime_data() as a notification mechanism - a
clever suggestion from Uli Schlachter.)

The advantage of this is that we aren't forcing the compositor to
do a frame cycle and send _NET_WM_FRAME_DRAWN - depending on how the
compositor is structured that might either cause it to do extra
work or it might send _NET_WM_FRAME_DRAWN early and upset frame
timing.

https://bugzilla.gnome.org/show_bug.cgi?id=685460

diff --git a/gdk/x11/gdkwindow-x11.c b/gdk/x11/gdkwindow-x11.c
index fbc13b56540aedb722fba3ac9f26e734328805db..f2c5735e79d5c8d26e6c7d4245c81547bbf2cf37 100644 (file)
--- a/gdk/x11/gdkwindow-x11.c
+++ b/gdk/x11/gdkwindow-x11.c
@@ -213,6 +213,70 @@ set_sync_counter(Display     *display,
     XSyncSetCounter(display, counter, sync_value);
 }
 
+static void
+window_pre_damage (GdkWindow *window)
+{
+  GdkWindow *toplevel_window = gdk_window_get_toplevel (window);
+  GdkWindowImplX11 *impl;
+
+  if (!toplevel_window || !WINDOW_IS_TOPLEVEL (toplevel_window))
+    return;
+
+  impl = GDK_WINDOW_IMPL_X11 (toplevel_window->impl);
+
+  if (impl->toplevel->in_frame &&
+      impl->toplevel->current_counter_value % 2 == 0)
+    {
+      impl->toplevel->current_counter_value += 1;
+      set_sync_counter(GDK_WINDOW_XDISPLAY (impl->wrapper),
+                      impl->toplevel->extended_update_counter,
+                      impl->toplevel->current_counter_value);
+    }
+}
+
+static void
+on_surface_changed (void *data)
+{
+  GdkWindow *window = data;
+
+  window_pre_damage (window);
+}
+
+/* We want to know when cairo drawing causes damage to the window,
+ * so we engage in the _NET_WM_FRAME_DRAWN protocol with the
+ * window only when there actually is drawing. To do that we use
+ * a technique (hack) suggested by Uli Schlachter - if we set
+ * a dummy "mime data" on the cairo surface (this facility is
+ * used to attach JPEG data to an imager), then cairo wil flush
+ * and remove the mime data before making any changes to the window.
+ */
+
+static void
+hook_surface_changed (GdkWindow *window)
+{
+  GdkWindowImplX11 *impl = GDK_WINDOW_IMPL_X11 (window->impl);
+
+  if (impl->cairo_surface)
+    cairo_surface_set_mime_data (impl->cairo_surface,
+                                 "x-gdk/change-notify",
+                                 (unsigned char *)"X",
+                                 1,
+                                 on_surface_changed,
+                                 window);
+}
+
+static void
+unhook_surface_changed (GdkWindow *window)
+{
+  GdkWindowImplX11 *impl = GDK_WINDOW_IMPL_X11 (window->impl);
+
+  if (impl->cairo_surface)
+    cairo_surface_set_mime_data (impl->cairo_surface,
+                                 "x-gdk/change-notify",
+                                 NULL, 0,
+                                 NULL, NULL);
+}
+
 static void
 gdk_x11_window_begin_frame (GdkWindow *window)
 {
@@ -226,13 +290,9 @@ gdk_x11_window_begin_frame (GdkWindow *window)
       impl->toplevel->extended_update_counter == None)
     return;
 
-  if (impl->toplevel->current_counter_value % 2 == 0)
-    {
-      impl->toplevel->current_counter_value += 1;
-      set_sync_counter(GDK_WINDOW_XDISPLAY (impl->wrapper),
-                      impl->toplevel->extended_update_counter,
-                      impl->toplevel->current_counter_value);
-    }
+  impl->toplevel->in_frame = TRUE;
+
+  hook_surface_changed (window);
 }
 
 static void
@@ -245,9 +305,12 @@ gdk_x11_window_end_frame (GdkWindow *window)
   impl = GDK_WINDOW_IMPL_X11 (window->impl);
 
   if (!WINDOW_IS_TOPLEVEL (window) ||
-      impl->toplevel->extended_update_counter == None)
+      impl->toplevel->extended_update_counter == None ||
+      !impl->toplevel->in_frame)
     return;
 
+  impl->toplevel->in_frame = FALSE;
+
   if (impl->toplevel->current_counter_value % 2 == 1)
     {
       impl->toplevel->current_counter_value += 1;
@@ -262,6 +325,8 @@ gdk_x11_window_end_frame (GdkWindow *window)
           gdk_frame_clock_freeze (gdk_window_get_frame_clock (window));
         }
     }
+
+  unhook_surface_changed (window);
 }
 
 /*****************************************************
@@ -307,6 +372,9 @@ gdk_x11_ref_cairo_surface (GdkWindow *window)
       if (impl->cairo_surface)
        cairo_surface_set_user_data (impl->cairo_surface, &gdk_x11_cairo_key,
                                     impl, gdk_x11_cairo_surface_destroy);
+
+      if (WINDOW_IS_TOPLEVEL (window) && impl->toplevel->in_frame)
+        hook_surface_changed (window);
     }
   else
     cairo_surface_reference (impl->cairo_surface);
@@ -326,6 +394,9 @@ gdk_window_impl_x11_finalize (GObject *object)
 
   wrapper = impl->wrapper;
 
+  if (WINDOW_IS_TOPLEVEL (wrapper) && impl->toplevel->in_frame)
+    unhook_surface_changed (wrapper);
+
   _gdk_x11_window_grab_check_destroy (wrapper);
 
   if (!GDK_WINDOW_DESTROYED (wrapper))
@@ -1569,6 +1640,8 @@ window_x11_move (GdkWindow *window,
 
   if (GDK_WINDOW_TYPE (window) == GDK_WINDOW_CHILD)
     {
+      /* The window isn't actually damaged, but it's parent is */
+      window_pre_damage (window);
       _gdk_x11_window_move_resize_child (window,
                                          x, y,
                                          window->width, window->height);
@@ -1598,6 +1671,8 @@ window_x11_resize (GdkWindow *window,
   if (height < 1)
     height = 1;
 
+  window_pre_damage (window);
+
   if (GDK_WINDOW_TYPE (window) == GDK_WINDOW_CHILD)
     {
       _gdk_x11_window_move_resize_child (window,
@@ -1641,6 +1716,8 @@ window_x11_move_resize (GdkWindow *window,
   if (height < 1)
     height = 1;
 
+  window_pre_damage (window);
+
   if (GDK_WINDOW_TYPE (window) == GDK_WINDOW_CHILD)
     {
       _gdk_x11_window_move_resize_child (window, x, y, width, height);

diff --git a/gdk/x11/gdkwindow-x11.h b/gdk/x11/gdkwindow-x11.h
index c42365222c98da1a2ceefc10ed1265d5636e7dc8..8dde33501197d990bbd39b43bf4b219037bfe51b 100644 (file)
--- a/gdk/x11/gdkwindow-x11.h
+++ b/gdk/x11/gdkwindow-x11.h
@@ -127,6 +127,8 @@ struct _GdkToplevelX11
    */
   guint have_focused : 1;
 
+  guint in_frame : 1;
+
   /* If we're expecting a response from the compositor after painting a frame */
   guint frame_pending : 1;