clutter/actor: Make get_transformed_paint_volume() transfer full

Transfer none was achieved using a stack GArray in the stage which
would get resized to 0 at the end of every frame to "free" it.
In the case of direct scanout however, painting the next frame only
happens after leaving fullscreen again. Until then the array just kept
growing and because GArrays don't reallocate when shrunk, this memory
remained allocated even after leaving fullscreen.

There is no cache benefit from storing paint volumes this way, because
nothing accesses them after their immediate use in the calling code.
Also the reduced overhead from avoiding malloc calls seems negligible as
according to heaptrack this only makes up about 2-3% of the temporary
allocations.

Changing this to transfer full and removing the stack array simplifies
the code and fixes the "leak".

Closes: https://gitlab.gnome.org/GNOME/mutter/-/issues/3191
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3442>

clutter/clutter/clutter-actor.c

@@ -1675,7 +1675,7 @@ set_show_on_set_parent (ClutterActor *self,
 static void
 clutter_actor_queue_redraw_on_parent (ClutterActor *self)
 {
-  const ClutterPaintVolume *pv;
+  g_autoptr (ClutterPaintVolume) pv = NULL;
 
   if (!self->priv->parent)
     return;
@@ -5584,7 +5584,7 @@ clutter_actor_real_get_paint_volume (ClutterActor       *self,
        child != NULL;
        child = child->priv->next_sibling)
     {
-      const ClutterPaintVolume *child_volume;
+      g_autoptr (ClutterPaintVolume) child_volume = NULL;
 
       /* we ignore unmapped children, since they won't be painted.
        *
@@ -14517,12 +14517,10 @@ clutter_actor_get_paint_volume (ClutterActor *self)
  * transformed paint volume of all of its children and union them
  * together using clutter_paint_volume_union().
  *
- * Return value: (transfer none) (nullable): a pointer to a #ClutterPaintVolume,
+ * Return value: (transfer full) (nullable): a pointer to a #ClutterPaintVolume,
- *   or %NULL if no volume could be determined. The returned pointer is
+ *   or %NULL if no volume could be determined.
- *   not guaranteed to be valid across multiple frames; if you wish to
- *   keep it, you will have to copy it using clutter_paint_volume_copy().
  */
-const ClutterPaintVolume *
+ClutterPaintVolume *
 clutter_actor_get_transformed_paint_volume (ClutterActor *self,
                                             ClutterActor *relative_to_ancestor)
 {
@@ -14541,10 +14539,7 @@ clutter_actor_get_transformed_paint_volume (ClutterActor *self,
   if (volume == NULL)
     return NULL;
 
-  transformed_volume =
+  transformed_volume = clutter_paint_volume_copy (volume);
-    _clutter_stage_paint_volume_stack_allocate (CLUTTER_STAGE (stage));
-
-  _clutter_paint_volume_copy_static (volume, transformed_volume);
 
   _clutter_paint_volume_transform_relative (transformed_volume,
                                             relative_to_ancestor);

clutter/clutter/clutter-actor.h

@@ -589,7 +589,7 @@ void                            clutter_actor_get_background_color
 CLUTTER_EXPORT
 const ClutterPaintVolume *      clutter_actor_get_paint_volume                  (ClutterActor               *self);
 CLUTTER_EXPORT
-const ClutterPaintVolume *      clutter_actor_get_transformed_paint_volume      (ClutterActor               *self,
+ClutterPaintVolume *            clutter_actor_get_transformed_paint_volume      (ClutterActor               *self,
                                                                                  ClutterActor               *relative_to_ancestor);
 
 /* Events */

clutter/clutter/clutter-stage.c

@@ -126,8 +126,6 @@ struct _ClutterStagePrivate
   GPtrArray *cur_event_actors;
   GArray *cur_event_emission_chain;
 
-  GArray *paint_volume_stack;
-
   GSList *pending_relayouts;
 
   int update_freeze_count;
@@ -441,8 +439,6 @@ clutter_stage_do_paint_view (ClutterStage     *stage,
       g_array_append_val (clip_frusta, clip_frustum);
     }
 
-  _clutter_stage_paint_volume_stack_free_all (stage);
-
   paint_flags = clutter_stage_view_get_default_paint_flags (view);
 
   paint_context = clutter_paint_context_new_for_view (view,
@@ -1290,8 +1286,6 @@ clutter_stage_finalize (GObject *object)
 
   g_free (priv->title);
 
-  g_array_free (priv->paint_volume_stack, TRUE);
-
   G_OBJECT_CLASS (clutter_stage_parent_class)->finalize (object);
 }
 
@@ -1694,9 +1688,6 @@ clutter_stage_init (ClutterStage *self)
   clutter_stage_set_title (self, g_get_prgname ());
   clutter_stage_set_key_focus (self, NULL);
   clutter_stage_set_viewport (self, geom.width, geom.height);
-
-  priv->paint_volume_stack =
-    g_array_new (FALSE, FALSE, sizeof (ClutterPaintVolume));
 }
 
 static void
@@ -2529,35 +2520,6 @@ clutter_stage_schedule_update (ClutterStage *stage)
   priv->update_scheduled = TRUE;
 }
 
-ClutterPaintVolume *
-_clutter_stage_paint_volume_stack_allocate (ClutterStage *stage)
-{
-  GArray *paint_volume_stack = stage->priv->paint_volume_stack;
-
-  g_array_set_size (paint_volume_stack,
-                    paint_volume_stack->len+1);
-
-  return &g_array_index (paint_volume_stack,
-                         ClutterPaintVolume,
-                         paint_volume_stack->len - 1);
-}
-
-void
-_clutter_stage_paint_volume_stack_free_all (ClutterStage *stage)
-{
-  GArray *paint_volume_stack = stage->priv->paint_volume_stack;
-  int i;
-
-  for (i = 0; i < paint_volume_stack->len; i++)
-    {
-      ClutterPaintVolume *pv =
-        &g_array_index (paint_volume_stack, ClutterPaintVolume, i);
-      clutter_paint_volume_free (pv);
-    }
-
-  g_array_set_size (paint_volume_stack, 0);
-}
-
 void
 clutter_stage_add_to_redraw_clip (ClutterStage       *stage,
                                   ClutterPaintVolume *redraw_clip)

src/compositor/meta-window-actor-x11.c

@@ -1351,7 +1351,7 @@ meta_window_actor_x11_get_paint_volume (ClutterActor       *actor,
   if (surface)
     {
       ClutterActor *surface_actor = CLUTTER_ACTOR (surface);
-      const ClutterPaintVolume *child_volume;
+      g_autoptr (ClutterPaintVolume) child_volume = NULL;
 
       child_volume = clutter_actor_get_transformed_paint_volume (surface_actor,
                                                                  actor);

src/compositor/meta-window-group.c

@@ -146,7 +146,7 @@ meta_window_group_get_paint_volume (ClutterActor       *self,
   clutter_actor_iter_init (&iter, self);
   while (clutter_actor_iter_next (&iter, &child))
     {
-      const ClutterPaintVolume *child_volume;
+      g_autoptr (ClutterPaintVolume) child_volume = NULL;
 
       if (!clutter_actor_is_mapped (child))
         continue;