[mutter] Distinguish "no delay" frames from spontaneous drawing

[Owen Taylor <otaylor src gnome org>]

commit 87fe9685b50c81481589b6748c188d152e8f0bd1
Author: Owen W. Taylor <otaylor fishsoup net>
Date:   Thu Nov 15 17:49:57 2012 -0500

    Distinguish "no delay" frames from spontaneous drawing
    
    When a client is drawing as hard as possible (without sleeping
    between frames) we need to draw as soon possible, since sleeping
    will decrease the effective frame rate shown to the user, and
    can also result in the system never kicking out of power-saving
    mode because it doesn't look fully utilized.
    
    Use the amount the client increments the counter value by when
    ending the frame to distinguish these cases:
    
     - Increment by 1: a no-delay frame
     - Increment by more than 1: a non-urgent frame, handle normally
    
    https://bugzilla.gnome.org/show_bug.cgi?id=685463

 src/compositor/meta-window-actor.c |    6 ++++++
 src/core/window-private.h          |    5 +++++
 src/core/window.c                  |    8 ++++++--
 3 files changed, 17 insertions(+), 2 deletions(-)
---
diff --git a/src/compositor/meta-window-actor.c b/src/compositor/meta-window-actor.c
index ce4ee59..f28452e 100644
--- a/src/compositor/meta-window-actor.c
+++ b/src/compositor/meta-window-actor.c
@@ -2355,6 +2355,12 @@ meta_window_actor_handle_updates (MetaWindowActor *self)
       priv->frames = g_list_prepend (priv->frames, frame);
 
       priv->window->needs_frame_drawn = FALSE;
+
+      if (priv->window->no_delay_frame)
+        {
+          ClutterActor *stage = clutter_actor_get_stage (CLUTTER_ACTOR (self));
+          clutter_stage_skip_sync_delay (CLUTTER_STAGE (stage));
+        }
     }
 }
 
diff --git a/src/core/window-private.h b/src/core/window-private.h
index 97b06ac..676a6ee 100644
--- a/src/core/window-private.h
+++ b/src/core/window-private.h
@@ -360,6 +360,11 @@ struct _MetaWindow
    * last update the sync request counter */
   guint needs_frame_drawn : 1;
 
+  /* if TRUE, the frame that was just drawn was drawn without any delay
+   * on the client's part and thus is high-priority - if we add delay
+   * we might cause the client to miss it's target frame rate */
+  guint no_delay_frame : 1;
+
   /* Note: can be NULL */
   GSList *struts;
 
diff --git a/src/core/window.c b/src/core/window.c
index 4b76e47..3c4026f 100644
--- a/src/core/window.c
+++ b/src/core/window.c
@@ -9509,8 +9509,12 @@ void
 meta_window_update_sync_request_counter (MetaWindow *window,
                                          gint64      new_counter_value)
 {
-  if (window->extended_sync_request_counter)
-    window->needs_frame_drawn = TRUE;
+  if (window->extended_sync_request_counter &&
+      new_counter_value % 2 == 0)
+    {
+      window->needs_frame_drawn = TRUE;
+      window->no_delay_frame = new_counter_value == window->sync_request_serial + 1;
+    }
 
   window->sync_request_serial = new_counter_value;
   meta_compositor_set_updates_frozen (window->display->compositor, window,