screen-cast/window: Add API to check if stream-cast is active

Screen-casted windows need to be considered visible in various situations
but existing APIs such as `clutter_actor_is_effectively_on_stage_view()`
don't do so. Add new API that allows checking if a surface belongs to a
screen-casted window for the respective cases.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2789>

src/backends/meta-screen-cast-window-stream.c

@@ -198,6 +198,16 @@ meta_screen_cast_window_stream_finalize (GObject *object)
 {
   MetaScreenCastWindowStream *window_stream =
     META_SCREEN_CAST_WINDOW_STREAM (object);
+  MetaWindowActor *window_actor;
+
+  window_actor = meta_window_actor_from_window (window_stream->window);
+  if (window_actor)
+    {
+      MetaScreenCastWindow *screen_cast_window;
+
+      screen_cast_window = META_SCREEN_CAST_WINDOW (window_actor);
+      meta_screen_cast_window_dec_usage (screen_cast_window);
+    }
 
   g_clear_signal_handler (&window_stream->window_unmanaged_handler_id,
                           window_stream->window);
@@ -218,6 +228,8 @@ meta_screen_cast_window_stream_initable_init (GInitable     *initable,
     meta_screen_cast_session_get_screen_cast (session);
   MetaBackend *backend = meta_screen_cast_get_backend (screen_cast);
   MetaWindow *window = window_stream->window;
+  MetaScreenCastWindow *screen_cast_window =
+    META_SCREEN_CAST_WINDOW (meta_window_actor_from_window (window));
   MetaLogicalMonitor *logical_monitor;
   int scale;
 
@@ -248,6 +260,8 @@ meta_screen_cast_window_stream_initable_init (GInitable     *initable,
   window_stream->stream_width = logical_monitor->rect.width * scale;
   window_stream->stream_height = logical_monitor->rect.height * scale;
 
+  meta_screen_cast_window_inc_usage (screen_cast_window);
+
   return initable_parent_iface->init (initable, cancellable, error);
 }
 

src/backends/meta-screen-cast-window.c

@@ -99,3 +99,15 @@ meta_screen_cast_window_has_damage (MetaScreenCastWindow *screen_cast_window)
 
   return iface->has_damage (screen_cast_window);
 }
+
+void
+meta_screen_cast_window_inc_usage (MetaScreenCastWindow *screen_cast_window)
+{
+  META_SCREEN_CAST_WINDOW_GET_IFACE (screen_cast_window)->inc_usage (screen_cast_window);
+}
+
+void
+meta_screen_cast_window_dec_usage (MetaScreenCastWindow *screen_cast_window)
+{
+  META_SCREEN_CAST_WINDOW_GET_IFACE (screen_cast_window)->dec_usage (screen_cast_window);
+}

src/backends/meta-screen-cast-window.h

@@ -62,6 +62,9 @@ struct _MetaScreenCastWindowInterface
                                    CoglFramebuffer      *framebuffer);
 
   gboolean (*has_damage) (MetaScreenCastWindow *screen_cast_window);
+
+  void (*inc_usage) (MetaScreenCastWindow *screen_cast_window);
+  void (*dec_usage) (MetaScreenCastWindow *screen_cast_window);
 };
 
 void meta_screen_cast_window_get_buffer_bounds (MetaScreenCastWindow *screen_cast_window,
@@ -90,6 +93,9 @@ gboolean meta_screen_cast_window_blit_to_framebuffer (MetaScreenCastWindow *scre
 
 gboolean meta_screen_cast_window_has_damage (MetaScreenCastWindow *screen_cast_window);
 
+void meta_screen_cast_window_inc_usage (MetaScreenCastWindow *screen_cast_window);
+void meta_screen_cast_window_dec_usage (MetaScreenCastWindow *screen_cast_window);
+
 G_END_DECLS
 
 #endif /* META_SCREEN_CAST_WINDOW_H */

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

@@ -101,6 +101,8 @@ void meta_window_actor_set_geometry_scale (MetaWindowActor *window_actor,
 
 int meta_window_actor_get_geometry_scale (MetaWindowActor *window_actor);
 
+gboolean meta_window_actor_is_streaming (MetaWindowActor *window_actor);
+
 void meta_window_actor_notify_damaged (MetaWindowActor *window_actor);
 
 gboolean meta_window_actor_is_frozen (MetaWindowActor *self);

src/compositor/meta-window-actor.c

@@ -69,6 +69,7 @@ typedef struct _MetaWindowActorPrivate
   gint              destroy_in_progress;
 
   guint             freeze_count;
+  guint             screen_cast_usage_count;
 
   guint		    visible                : 1;
   guint		    disposed               : 1;
@@ -1357,6 +1358,26 @@ meta_window_actor_has_damage (MetaScreenCastWindow *screen_cast_window)
   return clutter_actor_has_damage (CLUTTER_ACTOR (screen_cast_window));
 }
 
+static void
+meta_window_actor_inc_screen_cast_usage (MetaScreenCastWindow *screen_cast_window)
+{
+  MetaWindowActor *window_actor = META_WINDOW_ACTOR (screen_cast_window);
+  MetaWindowActorPrivate *priv =
+    meta_window_actor_get_instance_private (window_actor);
+
+  priv->screen_cast_usage_count++;
+}
+
+static void
+meta_window_actor_dec_screen_cast_usage (MetaScreenCastWindow *screen_cast_window)
+{
+  MetaWindowActor *window_actor = META_WINDOW_ACTOR (screen_cast_window);
+  MetaWindowActorPrivate *priv =
+    meta_window_actor_get_instance_private (window_actor);
+
+  priv->screen_cast_usage_count--;
+}
+
 static void
 screen_cast_window_iface_init (MetaScreenCastWindowInterface *iface)
 {
@@ -1366,6 +1387,17 @@ screen_cast_window_iface_init (MetaScreenCastWindowInterface *iface)
   iface->capture_into = meta_window_actor_capture_into;
   iface->blit_to_framebuffer = meta_window_actor_blit_to_framebuffer;
   iface->has_damage = meta_window_actor_has_damage;
+  iface->inc_usage = meta_window_actor_inc_screen_cast_usage;
+  iface->dec_usage = meta_window_actor_dec_screen_cast_usage;
+}
+
+gboolean
+meta_window_actor_is_streaming (MetaWindowActor *window_actor)
+{
+  MetaWindowActorPrivate *priv =
+    meta_window_actor_get_instance_private (window_actor);
+
+  return priv->screen_cast_usage_count > 0;
 }
 
 MetaWindowActor *