[mutter] clutter/actor: Don't traverse whole actor tree for updating stage-views

[Carlos Garnacho <carlosg src gnome org>]

commit 0f97196d84c038562fe3c8d11f9ef0e7593c412c
Author: Jonas Dreßler <verdre v0yd nl>
Date:   Fri Apr 10 01:19:00 2020 +0200

    clutter/actor: Don't traverse whole actor tree for updating stage-views
    
    We currently go through the whole tree of mapped actors on every paint
    cycle to update the stage views actors are on. Even if no actors need
    updating of their stage views, traversing the actor tree is still quite
    expensive and shows up when using a profiler.
    
    So tone down the amounts of full-tree traversals we have to do on every
    paint cycle and only traverse a subtree if it includes an actor which
    actually needs updating of its stage views.
    
    We do that by setting the `needs_update_stage_views` flag to TRUE
    recursively for all parents up to the stage when the stage-views list of
    an actor gets invalidated. This way we end up updating a few more actors
    than necessary, but can avoid searching the whole actor tree for actors
    which have `needs_update_stage_views` set to TRUE.
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1196

 clutter/clutter/clutter-actor.c | 40 ++++++++++++++++++++++++++++++++++------
 1 file changed, 34 insertions(+), 6 deletions(-)
---
diff --git a/clutter/clutter/clutter-actor.c b/clutter/clutter/clutter-actor.c
index dd7b1ba740..fe02d3abdd 100644
--- a/clutter/clutter/clutter-actor.c
+++ b/clutter/clutter/clutter-actor.c
@@ -1618,6 +1618,22 @@ clutter_actor_update_map_state (ClutterActor  *self,
 #endif
 }
 
+static void
+queue_update_stage_views (ClutterActor *actor)
+{
+  while (actor && !actor->priv->needs_update_stage_views)
+    {
+      actor->priv->needs_update_stage_views = TRUE;
+
+      /* We don't really need to update the stage-views of the actors up the
+       * hierarchy, we set the flag anyway though so we can avoid traversing
+       * the whole scenegraph when looking for actors which need an update
+       * in clutter_actor_update_stage_views().
+       */
+      actor = actor->priv->parent;
+    }
+}
+
 static void
 clutter_actor_real_map (ClutterActor *self)
 {
@@ -1632,6 +1648,18 @@ clutter_actor_real_map (ClutterActor *self)
 
   self->priv->needs_paint_volume_update = TRUE;
 
+  /* We skip unmapped actors when updating the stage-views list, so if
+   * an actors list got invalidated while it was unmapped make sure to
+   * set priv->needs_update_stage_views to TRUE for all actors up the
+   * hierarchy now.
+   */
+  if (self->priv->needs_update_stage_views)
+    {
+      /* Avoid the early return in queue_update_stage_views() */
+      self->priv->needs_update_stage_views = FALSE;
+      queue_update_stage_views (self);
+    }
+
   clutter_actor_ensure_resource_scale (self);
 
   /* notify on parent mapped before potentially mapping
@@ -2569,7 +2597,7 @@ static void
 absolute_allocation_changed (ClutterActor *actor)
 {
   actor->priv->needs_compute_resource_scale = TRUE;
-  actor->priv->needs_update_stage_views = TRUE;
+  queue_update_stage_views (actor);
 }
 
 static ClutterActorTraverseVisitFlags
@@ -17748,12 +17776,12 @@ clutter_actor_update_stage_views (ClutterActor *self)
       CLUTTER_ACTOR_IN_DESTRUCTION (self))
     return;
 
-  if (priv->needs_update_stage_views)
-    {
-      update_stage_views (self);
+  if (!priv->needs_update_stage_views)
+    return;
 
-      priv->needs_update_stage_views = FALSE;
-    }
+  update_stage_views (self);
+
+  priv->needs_update_stage_views = FALSE;
 
   for (child = priv->first_child; child; child = child->priv->next_sibling)
     clutter_actor_update_stage_views (child);