[mutter/gnome-42] window-actor: Add API to get the surface actor candidate for scanout

[Robert Mader <rmader src gnome org>]

commit c06962c7b36c4e419b31e6378d73a7faecb27cba
Author: Sebastian Keller <skeller gnome org>
Date:   Wed May 11 22:32:33 2022 +0200

    window-actor: Add API to get the surface actor candidate for scanout
    
    This replaces the API to get the topmost surface actor with an API to
    get the surface actor that could be a candidate for direct scanout. The
    advantage of this is that it allows X11 and Wayland specific
    restrictions for these actors.
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2409>
    
    (cherry picked from commit 9c8948fc047b8b99908a548a390f2acd1ccf8a55)

 src/compositor/meta-compositor-native.c    |  8 +++-----
 src/compositor/meta-window-actor-private.h |  4 ++--
 src/compositor/meta-window-actor-wayland.c | 19 +++++++++----------
 src/compositor/meta-window-actor-x11.c     | 18 ++++++++++++++++++
 src/compositor/meta-window-actor.c         | 12 ++++++------
 5 files changed, 38 insertions(+), 23 deletions(-)
---
diff --git a/src/compositor/meta-compositor-native.c b/src/compositor/meta-compositor-native.c
index 84e7a75d8b..bc17704e1b 100644
--- a/src/compositor/meta-compositor-native.c
+++ b/src/compositor/meta-compositor-native.c
@@ -114,13 +114,11 @@ maybe_assign_primary_plane (MetaCompositor *compositor)
   if (!COGL_IS_ONSCREEN (framebuffer))
     goto done;
 
-  surface_actor = meta_window_actor_get_topmost_surface (window_actor);
-  if (!surface_actor ||
-      CLUTTER_ACTOR (surface_actor) !=
-      clutter_actor_get_last_child (CLUTTER_ACTOR (window_actor)))
+  surface_actor = meta_window_actor_get_scanout_candidate (window_actor);
+  if (!surface_actor)
     goto done;
-  surface_actor_wayland = META_SURFACE_ACTOR_WAYLAND (surface_actor);
 
+  surface_actor_wayland = META_SURFACE_ACTOR_WAYLAND (surface_actor);
   surface = meta_surface_actor_wayland_get_surface (surface_actor_wayland);
   if (!surface)
     goto done;
diff --git a/src/compositor/meta-window-actor-private.h b/src/compositor/meta-window-actor-private.h
index 138ce2c832..8aa206bb83 100644
--- a/src/compositor/meta-window-actor-private.h
+++ b/src/compositor/meta-window-actor-private.h
@@ -15,7 +15,7 @@ struct _MetaWindowActorClass
                           ClutterFrameInfo *frame_info,
                           int64_t           presentation_time);
 
-  MetaSurfaceActor * (*get_topmost_surface) (MetaWindowActor *actor);
+  MetaSurfaceActor * (*get_scanout_candidate) (MetaWindowActor *actor);
 
   void (*assign_surface_actor) (MetaWindowActor  *actor,
                                 MetaSurfaceActor *surface_actor);
@@ -80,7 +80,7 @@ void meta_window_actor_effect_completed (MetaWindowActor  *actor,
 
 MetaSurfaceActor *meta_window_actor_get_surface (MetaWindowActor *self);
 
-MetaSurfaceActor * meta_window_actor_get_topmost_surface (MetaWindowActor *self);
+MetaSurfaceActor *meta_window_actor_get_scanout_candidate (MetaWindowActor *self);
 
 void meta_window_actor_assign_surface_actor (MetaWindowActor  *self,
                                              MetaSurfaceActor *surface_actor);
diff --git a/src/compositor/meta-window-actor-wayland.c b/src/compositor/meta-window-actor-wayland.c
index 468229751f..4b87fd11fb 100644
--- a/src/compositor/meta-window-actor-wayland.c
+++ b/src/compositor/meta-window-actor-wayland.c
@@ -89,19 +89,18 @@ meta_window_actor_wayland_rebuild_surface_tree (MetaWindowActor *actor)
 }
 
 static MetaSurfaceActor *
-meta_window_actor_wayland_get_topmost_surface (MetaWindowActor *actor)
+meta_window_actor_wayland_get_scanout_candidate (MetaWindowActor *actor)
 {
   ClutterActor *child_actor;
+  MetaSurfaceActor *topmost_surface_actor;
 
-  for (child_actor = clutter_actor_get_last_child (CLUTTER_ACTOR (actor));
-       child_actor;
-       child_actor = clutter_actor_get_previous_sibling (child_actor))
-    {
-      if (META_IS_SURFACE_ACTOR_WAYLAND (child_actor))
-        return META_SURFACE_ACTOR (child_actor);
-    }
+  child_actor = clutter_actor_get_last_child (CLUTTER_ACTOR (actor));
+  if (!child_actor || !META_IS_SURFACE_ACTOR_WAYLAND (child_actor))
+    return NULL;
+
+  topmost_surface_actor = META_SURFACE_ACTOR (child_actor);
 
-  return NULL;
+  return topmost_surface_actor;
 }
 
 static void
@@ -193,7 +192,7 @@ meta_window_actor_wayland_class_init (MetaWindowActorWaylandClass *klass)
   MetaWindowActorClass *window_actor_class = META_WINDOW_ACTOR_CLASS (klass);
   GObjectClass *object_class = G_OBJECT_CLASS (klass);
 
-  window_actor_class->get_topmost_surface = meta_window_actor_wayland_get_topmost_surface;
+  window_actor_class->get_scanout_candidate = meta_window_actor_wayland_get_scanout_candidate;
   window_actor_class->assign_surface_actor = meta_window_actor_wayland_assign_surface_actor;
   window_actor_class->frame_complete = meta_window_actor_wayland_frame_complete;
   window_actor_class->queue_frame_drawn = meta_window_actor_wayland_queue_frame_drawn;
diff --git a/src/compositor/meta-window-actor-x11.c b/src/compositor/meta-window-actor-x11.c
index 9e64462ea8..d06855b51c 100644
--- a/src/compositor/meta-window-actor-x11.c
+++ b/src/compositor/meta-window-actor-x11.c
@@ -431,6 +431,23 @@ meta_window_actor_x11_frame_complete (MetaWindowActor  *actor,
     }
 }
 
+static MetaSurfaceActor *
+meta_window_actor_x11_get_scanout_candidate (MetaWindowActor *actor)
+{
+  MetaSurfaceActor *surface_actor;
+
+  surface_actor = meta_window_actor_get_surface (actor);
+
+  if (!surface_actor)
+    return NULL;
+
+  if (CLUTTER_ACTOR (surface_actor) !=
+      clutter_actor_get_last_child (CLUTTER_ACTOR (actor)))
+    return NULL;
+
+  return surface_actor;
+}
+
 static void
 surface_size_changed (MetaSurfaceActor *actor,
                       gpointer          user_data)
@@ -1681,6 +1698,7 @@ meta_window_actor_x11_class_init (MetaWindowActorX11Class *klass)
   GParamSpec *pspec;
 
   window_actor_class->frame_complete = meta_window_actor_x11_frame_complete;
+  window_actor_class->get_scanout_candidate = meta_window_actor_x11_get_scanout_candidate;
   window_actor_class->assign_surface_actor = meta_window_actor_x11_assign_surface_actor;
   window_actor_class->queue_frame_drawn = meta_window_actor_x11_queue_frame_drawn;
   window_actor_class->before_paint = meta_window_actor_x11_before_paint;
diff --git a/src/compositor/meta-window-actor.c b/src/compositor/meta-window-actor.c
index 9cee56a371..ae1fa4d903 100644
--- a/src/compositor/meta-window-actor.c
+++ b/src/compositor/meta-window-actor.c
@@ -107,7 +107,7 @@ static void meta_window_actor_get_property (GObject      *object,
                                             GValue       *value,
                                             GParamSpec   *pspec);
 
-static MetaSurfaceActor * meta_window_actor_real_get_topmost_surface (MetaWindowActor *self);
+static MetaSurfaceActor * meta_window_actor_real_get_scanout_candidate (MetaWindowActor *self);
 
 static void meta_window_actor_real_assign_surface_actor (MetaWindowActor  *self,
                                                          MetaSurfaceActor *surface_actor);
@@ -132,7 +132,7 @@ meta_window_actor_class_init (MetaWindowActorClass *klass)
   object_class->get_property = meta_window_actor_get_property;
   object_class->constructed  = meta_window_actor_constructed;
 
-  klass->get_topmost_surface = meta_window_actor_real_get_topmost_surface;
+  klass->get_scanout_candidate = meta_window_actor_real_get_scanout_candidate;
   klass->assign_surface_actor = meta_window_actor_real_assign_surface_actor;
 
   /**
@@ -560,15 +560,15 @@ meta_window_actor_get_surface (MetaWindowActor *self)
 }
 
 static MetaSurfaceActor *
-meta_window_actor_real_get_topmost_surface (MetaWindowActor *self)
+meta_window_actor_real_get_scanout_candidate (MetaWindowActor *self)
 {
-  return meta_window_actor_get_surface (self);
+  return NULL;
 }
 
 MetaSurfaceActor *
-meta_window_actor_get_topmost_surface (MetaWindowActor *self)
+meta_window_actor_get_scanout_candidate (MetaWindowActor *self)
 {
-  return META_WINDOW_ACTOR_GET_CLASS (self)->get_topmost_surface (self);
+  return META_WINDOW_ACTOR_GET_CLASS (self)->get_scanout_candidate (self);
 }
 
 /**