[mutter] window-group: Improve performance by hacking around Clutter

[Jasper St. Pierre <jstpierre src gnome org>]

commit ccca810daf08c0f7ef415afb6b6c7389f6553d35
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Sun Jul 5 19:18:22 2015 -0700

    window-group: Improve performance by hacking around Clutter
    
    The comment explains it better, but Clutter tries to be smart and
    repaint actors when their allocations change. Since the window group's
    allocation changes when windows move around, this means that moving a
    window will always cause a full-stage repaint, which is super slow.
    
    Hack around this for now.

 src/compositor/meta-window-group.c |   34 +++++++++++++++++++++++++++++++++-
 1 files changed, 33 insertions(+), 1 deletions(-)
---
diff --git a/src/compositor/meta-window-group.c b/src/compositor/meta-window-group.c
index cb4ade4..3a024b2 100644
--- a/src/compositor/meta-window-group.c
+++ b/src/compositor/meta-window-group.c
@@ -145,13 +145,45 @@ meta_window_group_get_paint_volume (ClutterActor       *self,
   return TRUE;
 }
 
+/* This is a workaround for Clutter's awful allocation tracking.
+ * Without this, any time the window group changed size, which is
+ * any time windows are dragged around, we'll do a full repaint
+ * of the window group, which includes the background actor, meaning
+ * a full-stage repaint.
+ *
+ * Since actors are allowed to paint outside their allocation, and
+ * since child actors are allowed to be outside their parents, this
+ * doesn't affect anything, but it means that we'll get much more
+ * sane and consistent clipped repaints from Clutter. */
+static void
+meta_window_group_get_preferred_width (ClutterActor *actor,
+                                       gfloat        for_height,
+                                       gfloat       *min_width,
+                                       gfloat       *nat_width)
+{
+  *min_width = 0;
+  *nat_width = 0;
+}
+
+static void
+meta_window_group_get_preferred_height (ClutterActor *actor,
+                                        gfloat        for_width,
+                                        gfloat       *min_height,
+                                        gfloat       *nat_height)
+{
+  *min_height = 0;
+  *nat_height = 0;
+}
+
 static void
 meta_window_group_class_init (MetaWindowGroupClass *klass)
 {
   ClutterActorClass *actor_class = CLUTTER_ACTOR_CLASS (klass);
 
-  actor_class->paint = meta_window_group_paint;
+  if (0) actor_class->paint = meta_window_group_paint;
   actor_class->get_paint_volume = meta_window_group_get_paint_volume;
+  actor_class->get_preferred_width = meta_window_group_get_preferred_width;
+  actor_class->get_preferred_height = meta_window_group_get_preferred_height;
 }
 
 static void