broadway: Sync surface updates with paint clock

We now only update surface data after we have painted. Before we painted
in an idle, which meant we might send black data some times if we e.g.
resized the window and had not painted yet. Also, it means we're updating
less often to the daemon, saving resources.

We still have to queue a flush in the idle for non-draw operations,
otherwise e.g. resize of a toplevel will never be flushed if the clock
is frozen (e.g. during toplevel resize).

gdk/broadway/gdkwindow-broadway.c

@@ -83,18 +83,16 @@ G_DEFINE_TYPE (GdkWindowImplBroadway,
 	       gdk_window_impl_broadway,
 	       GDK_TYPE_WINDOW_IMPL)
 
-static guint dirty_flush_id = 0;
-
-static gboolean
-dirty_flush_idle (gpointer data)
+static void
+update_dirty_windows_and_sync (void)
 {
   GList *l;
   GdkBroadwayDisplay *display;
-
-  dirty_flush_id = 0;
+  gboolean updated_surface;
 
   display = GDK_BROADWAY_DISPLAY (gdk_display_get_default ());
 
+  updated_surface = FALSE;
   for (l = display->toplevels; l != NULL; l = l->next)
     {
       GdkWindowImplBroadway *impl = l->data;
@@ -102,6 +100,7 @@ dirty_flush_idle (gpointer data)
       if (impl->dirty)
 	{
 	  impl->dirty = FALSE;
+	  updated_surface = TRUE;
 	  _gdk_broadway_server_window_update (display->server,
 					      impl->id,
 					      impl->surface);
@@ -110,16 +109,32 @@ dirty_flush_idle (gpointer data)
 
   /* We sync here to ensure all references to the impl->surface memory
      is done, as we may later paint new data in them. */
-  gdk_display_sync (GDK_DISPLAY (display));
+  if (updated_surface)
+    gdk_display_sync (GDK_DISPLAY (display));
+  else
+    gdk_display_flush (GDK_DISPLAY (display));
+}
+
+static guint flush_id = 0;
+
+static gboolean
+flush_idle (gpointer data)
+{
+  flush_id = 0;
+
+  gdk_display_flush (gdk_display_get_default ());
 
   return FALSE;
 }
 
+/* We need to flush in an idle rather than AFTER_PAINT, as the clock
+   is frozen during e.g. window resizes so the paint will not happen
+   and the window resize request is never flushed. */
 static void
-queue_dirty_flush (GdkBroadwayDisplay *display)
+queue_flush (GdkWindow *window)
 {
-  if (dirty_flush_id == 0)
-    dirty_flush_id = gdk_threads_add_idle (dirty_flush_idle, NULL);
+  if (flush_id == 0)
+    flush_id = gdk_threads_add_idle (flush_idle, NULL);
 }
 
 static void
@@ -197,6 +212,25 @@ _gdk_broadway_screen_init_root_window (GdkScreen * screen)
   _gdk_window_update_size (broadway_screen->root_window);
 }
 
+static void
+on_frame_clock_after_paint (GdkFrameClock *clock,
+                            GdkWindow     *window)
+{
+  update_dirty_windows_and_sync ();
+}
+
+static void
+connect_frame_clock (GdkWindow *window)
+{
+  if (WINDOW_IS_TOPLEVEL (window))
+    {
+      GdkFrameClock *frame_clock = gdk_window_get_frame_clock (window);
+
+      g_signal_connect (frame_clock, "after-paint",
+                        G_CALLBACK (on_frame_clock_after_paint), window);
+    }
+}
+
 void
 _gdk_broadway_display_create_window_impl (GdkDisplay    *display,
 					  GdkWindow     *window,
@@ -229,6 +263,8 @@ _gdk_broadway_display_create_window_impl (GdkDisplay    *display,
   g_assert (GDK_WINDOW_TYPE (window->parent) == GDK_WINDOW_ROOT);
 
   broadway_display->toplevels = g_list_prepend (broadway_display->toplevels, impl);
+
+  connect_frame_clock (window);
 }
 
 void
@@ -384,7 +420,7 @@ gdk_window_broadway_show (GdkWindow *window, gboolean already_mapped)
 
   broadway_display = GDK_BROADWAY_DISPLAY (gdk_window_get_display (window));
   if (_gdk_broadway_server_window_show (broadway_display->server, impl->id))
-    queue_dirty_flush (broadway_display);
+    queue_flush (window);
 
 }
 
@@ -405,7 +441,7 @@ gdk_window_broadway_hide (GdkWindow *window)
 
   broadway_display = GDK_BROADWAY_DISPLAY (gdk_window_get_display (window));
   if (_gdk_broadway_server_window_hide (broadway_display->server, impl->id))
-    queue_dirty_flush (broadway_display);
+    queue_flush (window);
 
   _gdk_window_clear_update_area (window);
 }
@@ -460,7 +496,7 @@ gdk_window_broadway_move_resize (GdkWindow *window,
 					   with_move,
 					   x, y,
 					   window->width, window->height);
-  queue_dirty_flush (broadway_display);
+  queue_flush (window);
   if (size_changed)
     window->resize_count++;
 }
@@ -1327,7 +1363,6 @@ gdk_broadway_window_process_updates_recurse (GdkWindow *window,
 
   impl = GDK_WINDOW_IMPL_BROADWAY (window->impl);
   impl->dirty = TRUE;
-  queue_dirty_flush (GDK_BROADWAY_DISPLAY (gdk_window_get_display (window)));
 }
 
 void
@@ -1393,7 +1428,7 @@ _gdk_broadway_window_translate (GdkWindow      *window,
       if (_gdk_broadway_server_window_translate (broadway_display->server,
 						 impl->id,
 						 area, dx, dy))
-	queue_dirty_flush (broadway_display);
+	queue_flush (window);
     }
 }