f7658ac5f0
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 (cherry picked from commit 2fb3db7659caa3627a473fefabc4d6a87f688cee)