window-actor: Add a new can_freeze_commits() API

Mutter freezes Xwayland commits when resizing windows, and thaw them in
the window actors' after_paint() for X11.

Yet, after_paint() could be never called, as when a new window is mapped
while the overview is active in gnome-shell.

As a result, the content of the X11 window will remain invisible to the
overview.

Add a new window actor API to tell whether commits can be frozen. For
Wayland window actors, this always return FALSE, whereas for X11 window
actors, it checks whether the Clutter actor is mapped.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1678>

src/compositor/meta-window-actor-private.h

@@ -32,6 +32,7 @@ struct _MetaWindowActorClass
   void (*set_frozen) (MetaWindowActor *actor,
                       gboolean         frozen);
   void (*update_regions) (MetaWindowActor *actor);
+  gboolean (*can_freeze_commits) (MetaWindowActor *actor);
 };
 
 typedef enum
@@ -96,4 +97,6 @@ gboolean meta_window_actor_is_opaque (MetaWindowActor *self);
 
 void meta_window_actor_update_regions (MetaWindowActor *self);
 
+gboolean meta_window_actor_can_freeze_commits (MetaWindowActor *self);
+
 #endif /* META_WINDOW_ACTOR_PRIVATE_H */

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

@@ -146,6 +146,12 @@ meta_window_actor_wayland_update_regions (MetaWindowActor *actor)
 {
 }
 
+static gboolean
+meta_window_actor_wayland_can_freeze_commits (MetaWindowActor *actor)
+{
+  return FALSE;
+}
+
 static void
 meta_window_actor_wayland_class_init (MetaWindowActorWaylandClass *klass)
 {
@@ -159,6 +165,7 @@ meta_window_actor_wayland_class_init (MetaWindowActorWaylandClass *klass)
   window_actor_class->queue_destroy = meta_window_actor_wayland_queue_destroy;
   window_actor_class->set_frozen = meta_window_actor_wayland_set_frozen;
   window_actor_class->update_regions = meta_window_actor_wayland_update_regions;
+  window_actor_class->can_freeze_commits = meta_window_actor_wayland_can_freeze_commits;
 }
 
 static void

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

@@ -1458,6 +1458,14 @@ meta_window_actor_x11_update_regions (MetaWindowActor *actor)
   update_regions (META_WINDOW_ACTOR_X11 (actor));
 }
 
+static gboolean
+meta_window_actor_x11_can_freeze_commits (MetaWindowActor *actor)
+{
+  ClutterActor *clutter_actor = CLUTTER_ACTOR (actor);
+
+  return clutter_actor_is_mapped (clutter_actor);
+}
+
 static void
 meta_window_actor_x11_set_property (GObject      *object,
                                     guint         prop_id,
@@ -1632,6 +1640,7 @@ meta_window_actor_x11_class_init (MetaWindowActorX11Class *klass)
   window_actor_class->queue_destroy = meta_window_actor_x11_queue_destroy;
   window_actor_class->set_frozen = meta_window_actor_x11_set_frozen;
   window_actor_class->update_regions = meta_window_actor_x11_update_regions;
+  window_actor_class->can_freeze_commits = meta_window_actor_x11_can_freeze_commits;
 
   actor_class->paint = meta_window_actor_x11_paint;
   actor_class->get_paint_volume = meta_window_actor_x11_get_paint_volume;

src/compositor/meta-window-actor.c

@@ -257,6 +257,14 @@ meta_window_actor_update_regions (MetaWindowActor *self)
   META_WINDOW_ACTOR_GET_CLASS (self)->update_regions (self);
 }
 
+gboolean
+meta_window_actor_can_freeze_commits (MetaWindowActor *self)
+{
+  g_return_val_if_fail (META_IS_WINDOW_ACTOR (self), FALSE);
+
+  return META_WINDOW_ACTOR_GET_CLASS (self)->can_freeze_commits (self);
+}
+
 static void
 meta_window_actor_set_frozen (MetaWindowActor *self,
                               gboolean         frozen)