Comment 10 for bug 1751593

Quick update - I have been looking into this lately to see if we could use Pekka's proposal of adding an _XWAYLAND_ALLOW_COMMITS property to tell Xwayland when to commit the surface:

  https://lists.x.org/archives/xorg-devel/2016-November/051913.html
  https://lists.x.org/archives/xorg-devel/2016-December/051947.html

and

  https://patchwork.freedesktop.org/series/16610/

Before so, I tried to understand what would be causing the back border issue in the first place and traced it down to meta_window_actor_update_opaque_region().

And it's not called from the same code path when using an application that uses _NET_WM_SYNC protocol (e.g. gtk-demo from gtk2) and one who doesn't (e.g. plain old xterm).

With XSync protocol:

  meta_window_x11_update_sync_request_counter()
    meta_compositor_sync_updates_frozen()
      meta_window_actor_sync_updates_frozen()
        meta_window_actor_set_updates_frozen()
          meta_window_actor_thaw()
              meta_window_actor_handle_updates()
              check_needs_reshape()
                meta_window_actor_update_opaque_region();

Without XSync protocol:

  clutter_clock_dispatch()
    master_clock_update_stages()
      _clutter_run_repaint_functions()
        meta_window_actor_pre_paint()
          meta_window_actor_handle_updates()
            check_needs_reshape()
              meta_window_actor_update_opaque_region();