[mutter] window-actor/x11: Get frame rect from the buffer size

[Robert Mader <rmader src gnome org>]

commit 1ce933e281ec6d9333b318ef485465e1cdf8b9c1
Author: Olivier Fourdan <ofourdan redhat com>
Date:   Fri Jan 17 18:11:03 2020 +0100

    window-actor/x11: Get frame rect from the buffer size
    
    When building the frame mask, the current reported frame size may not
    match when is actually on screen if the buffer has not been updated
    yet.
    
    So instead of getting the frame size from the meta window, deduce it
    from the texture size.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/1009

 src/compositor/meta-window-actor-x11.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)
---
diff --git a/src/compositor/meta-window-actor-x11.c b/src/compositor/meta-window-actor-x11.c
index cd2aa2edd..4f20336d8 100644
--- a/src/compositor/meta-window-actor-x11.c
+++ b/src/compositor/meta-window-actor-x11.c
@@ -892,7 +892,16 @@ build_and_scan_frame_mask (MetaWindowActorX11    *actor_x11,
       cairo_rectangle_int_t rect = { 0, 0, tex_width, tex_height };
       cairo_rectangle_int_t frame_rect;
 
-      meta_window_get_frame_rect (window, &frame_rect);
+      /* If we update the shape regardless of the frozen state of the actor,
+       * as with Xwayland to avoid the black shadow effect, we ought to base
+       * the frame size on the buffer size rather than the reported window's
+       * frame size, as the buffer may not have been committed yet at this
+       * point.
+       */
+      if (meta_window_x11_always_update_shape (window))
+        meta_window_x11_buffer_rect_to_frame_rect (window, &rect, &frame_rect);
+      else
+        meta_window_get_frame_rect (window, &frame_rect);
 
       /* Make sure we don't paint the frame over the client window. */
       frame_paint_region = cairo_region_create_rectangle (&rect);