[mutter] compositor: Skip windows not visible to the compositor

[Olivier Fourdan <ofourdan src gnome org>]

commit 2fb3db7659caa3627a473fefabc4d6a87f688cee
Author: Olivier Fourdan <ofourdan redhat com>
Date:   Wed Sep 19 16:08:52 2018 +0200

    compositor: Skip windows not visible to the compositor
    
    The compositor will automatically unredirect the top most window which
    is fully visible on screen. When unredirecting windows, it also shapes
    the compositor overlay window (COW) so that other redirected windows
    still shows correctly.
    
    The function `get_top_visible_window_actor()` however will simply walks
    down the window list, so if a window is placed on a layer above and
    unredirected, then iconified by the client, it will still be picked up
    by `get_top_visible_window_actor()` and he compositor will reckon it's
    still unredirected while not in a visible state anymore, thus leaving a
    black area on screen.
    
    Make sure we skip the windows not known to the compositor while picking
    the top visible window actor to avoid this issue.
    
    Closes: https://gitlab.gnome.org/GNOME/mutter/issues/306

 src/compositor/compositor.c | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/src/compositor/compositor.c b/src/compositor/compositor.c
index e45d10c00..e1f597346 100644
--- a/src/compositor/compositor.c
+++ b/src/compositor/compositor.c
@@ -804,6 +804,7 @@ meta_compositor_hide_window (MetaCompositor *compositor,
 {
   MetaWindowActor *window_actor = META_WINDOW_ACTOR (meta_window_get_compositor_private (window));
   meta_window_actor_hide (window_actor, effect);
+  meta_stack_tracker_queue_sync_stack (compositor->display->stack_tracker);
 }
 
 void
@@ -951,6 +952,9 @@ get_top_visible_window_actor (MetaCompositor *compositor)
       MetaRectangle buffer_rect;
       MetaRectangle display_rect = { 0 };
 
+      if (!window->visible_to_compositor)
+        continue;
+
       meta_window_get_buffer_rect (window, &buffer_rect);
       meta_display_get_size (compositor->display,
                              &display_rect.width, &display_rect.height);