[mutter] Optimize out restacks that don't change actor order

[Owen Taylor <otaylor src gnome org>]

commit bac668d287deebee928f73d8938cc32ac73646ef
Author: Owen W. Taylor <otaylor fishsoup net>
Date:   Sat Nov 13 14:45:01 2010 -0500

    Optimize out restacks that don't change actor order
    
    For various reasons (mostly the stack tracker correctly predicting the
    stacking order before getting events, but also because of the processing
    that the compositor does to get the actor stacking order) the compositor
    can be told to sync the stack when it has nothing to do. Detect this
    at the last moment before actually telling Clutter to restack to avoid
    triggering unnecessary redraws.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=634771

 src/compositor/compositor.c |   49 ++++++++++++++++++++++++++++++++++++------
 1 files changed, 42 insertions(+), 7 deletions(-)
---
diff --git a/src/compositor/compositor.c b/src/compositor/compositor.c
index ad964b6..7eb10de 100644
--- a/src/compositor/compositor.c
+++ b/src/compositor/compositor.c
@@ -34,7 +34,7 @@ composite_at_least_version (MetaDisplay *display, int maj, int min)
   return (major > maj || (major == maj && minor >= min));
 }
 
-static void sync_actor_stacking (GList *windows);
+static void sync_actor_stacking (MetaCompScreen *info);
 
 static void
 meta_finish_workspace_switch (MetaCompScreen *info)
@@ -48,7 +48,7 @@ meta_finish_workspace_switch (MetaCompScreen *info)
   /*
    * Fix up stacking order in case the plugin messed it up.
    */
-  sync_actor_stacking (info->windows);
+  sync_actor_stacking (info);
 
 /*   printf ("... FINISHED DESKTOP SWITCH\n"); */
 
@@ -87,7 +87,7 @@ add_win (MetaWindow *window)
 
   meta_window_actor_new (window);
 
-  sync_actor_stacking (info->windows);
+  sync_actor_stacking (info);
 }
 
 static void
@@ -827,13 +827,48 @@ meta_compositor_switch_workspace (MetaCompositor     *compositor,
 }
 
 static void
-sync_actor_stacking (GList *windows)
+sync_actor_stacking (MetaCompScreen *info)
 {
+  GList *children;
   GList *tmp;
+  GList *old;
+  gboolean reordered;
 
-  /* NB: The first entry in the list is stacked the lowest */
+  /* NB: The first entries in the lists are stacked the lowest */
 
-  for (tmp = g_list_last (windows); tmp != NULL; tmp = tmp->prev)
+  /* Restacking will trigger full screen redraws, so it's worth a
+   * little effort to make sure we actually need to restack before
+   * we go ahead and do it */
+
+  children = clutter_container_get_children (CLUTTER_CONTAINER (info->window_group));
+  reordered = FALSE;
+
+  old = children;
+  for (tmp = info->windows; tmp != NULL; tmp = tmp->next)
+    {
+      while (old && !META_IS_WINDOW_ACTOR (old->data))
+        old = old->next;
+
+      /* old == NULL: someone reparented a window out of the window group,
+       * order undefined, always restack */
+      if (old == NULL || old->data != tmp->data)
+        {
+          reordered = TRUE;
+          break;
+        }
+
+      old = old->next;
+    }
+
+  if (old != NULL) /* An extra MetaWindowActor??? .... restack */
+    reordered = TRUE;
+
+  g_list_free (children);
+
+  if (!reordered)
+    return;
+
+  for (tmp = g_list_last (info->windows); tmp != NULL; tmp = tmp->prev)
     {
       MetaWindowActor *window_actor = tmp->data;
 
@@ -927,7 +962,7 @@ meta_compositor_sync_stack (MetaCompositor  *compositor,
       old_stack = g_list_remove (old_stack, actor);
     }
 
-  sync_actor_stacking (info->windows);
+  sync_actor_stacking (info);
 }
 
 void