From f7768874e5ec2a808ccec424ed9e238e3dc13987 Mon Sep 17 00:00:00 2001
From: Robert Mader <robert.mader@posteo.de>
Date: Fri, 16 Apr 2021 15:15:41 +0200
Subject: [PATCH] window-actor/wayland: Cleaner subsurface reordering

Currently when reordering subsurfaces, we un- and reparent all child
actors of the window actor. This is unnecessarily wasteful and
triggers bugs in clutter. While the underlying issue should be fixed
eventually, simply reorder the actors with the tools clutter provides
us with, avoiding those bugs and likely being faster as well.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1831>
---
 src/compositor/meta-window-actor-wayland.c | 67 +++++++++++-----------
 1 file changed, 32 insertions(+), 35 deletions(-)

diff --git a/src/compositor/meta-window-actor-wayland.c b/src/compositor/meta-window-actor-wayland.c
index 7c3be5690..b1fe61641 100644
--- a/src/compositor/meta-window-actor-wayland.c
+++ b/src/compositor/meta-window-actor-wayland.c
@@ -32,37 +32,36 @@ struct _MetaWindowActorWayland
 
 G_DEFINE_TYPE (MetaWindowActorWayland, meta_window_actor_wayland, META_TYPE_WINDOW_ACTOR)
 
+typedef struct _SurfaceTreeTraverseData
+{
+  MetaWindowActor *window_actor;
+  int index;
+} SurfaceTreeTraverseData;
+
 static gboolean
-remove_surface_actor_from_children (GNode    *node,
-                                    gpointer  data)
+set_surface_actor_index (GNode    *node,
+                         gpointer  data)
 {
   MetaWaylandSurface *surface = node->data;
   MetaSurfaceActor *surface_actor = meta_wayland_surface_get_actor (surface);
-  MetaWindowActor *window_actor = data;
-  ClutterActor *parent;
+  SurfaceTreeTraverseData *traverse_data = data;
 
-  parent = clutter_actor_get_parent (CLUTTER_ACTOR (surface_actor));
-  if (!parent)
-    return FALSE;
-
-  g_return_val_if_fail (parent == CLUTTER_ACTOR (window_actor), FALSE);
-
-  clutter_actor_remove_child (CLUTTER_ACTOR (window_actor),
-                              CLUTTER_ACTOR (surface_actor));
-
-  return FALSE;
-}
-
-static gboolean
-add_surface_actor_to_children (GNode    *node,
-                               gpointer  data)
-{
-  MetaWaylandSurface *surface = node->data;
-  MetaSurfaceActor *surface_actor = meta_wayland_surface_get_actor (surface);
-  MetaWindowActor *window_actor = data;
-
-  clutter_actor_add_child (CLUTTER_ACTOR (window_actor),
-                           CLUTTER_ACTOR (surface_actor));
+  if (clutter_actor_contains (CLUTTER_ACTOR (traverse_data->window_actor),
+                              CLUTTER_ACTOR (surface_actor)))
+    {
+      clutter_actor_set_child_at_index (
+        CLUTTER_ACTOR (traverse_data->window_actor),
+        CLUTTER_ACTOR (surface_actor),
+        traverse_data->index);
+    }
+  else
+    {
+      clutter_actor_insert_child_at_index (
+        CLUTTER_ACTOR (traverse_data->window_actor),
+        CLUTTER_ACTOR (surface_actor),
+        traverse_data->index);
+    }
+  traverse_data->index++;
 
   return FALSE;
 }
@@ -75,20 +74,18 @@ meta_window_actor_wayland_rebuild_surface_tree (MetaWindowActor *actor)
   MetaWaylandSurface *surface = meta_surface_actor_wayland_get_surface (
     META_SURFACE_ACTOR_WAYLAND (surface_actor));
   GNode *root_node = surface->subsurface_branch_node;
+  SurfaceTreeTraverseData traverse_data;
 
+  traverse_data = (SurfaceTreeTraverseData) {
+    .window_actor = actor,
+    .index = 0,
+  };
   g_node_traverse (root_node,
                    G_IN_ORDER,
                    G_TRAVERSE_LEAVES,
                    -1,
-                   remove_surface_actor_from_children,
-                   actor);
-
-  g_node_traverse (root_node,
-                   G_IN_ORDER,
-                   G_TRAVERSE_LEAVES,
-                   -1,
-                   add_surface_actor_to_children,
-                   actor);
+                   set_surface_actor_index,
+                   &traverse_data);
 }
 
 static void