[mutter] stage: Queue redraw previous Rect only if it has changed

[Jonas Ådahl <jadahl src gnome org>]

commit 42953a50bbe5bd7f6318c6a9f6a588a874392094
Author: Marco Trevisan (Treviño) <mail 3v1n0 net>
Date:   Thu Feb 28 23:02:59 2019 +0100

    stage: Queue redraw previous Rect only if it has changed
    
    No need to queue redraw the same area multiple times, so we can avoid the
    computation involved with it.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/3

 src/backends/meta-stage.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)
---
diff --git a/src/backends/meta-stage.c b/src/backends/meta-stage.c
index 425926a7c..1f0d9c050 100644
--- a/src/backends/meta-stage.c
+++ b/src/backends/meta-stage.c
@@ -123,8 +123,11 @@ meta_overlay_paint (MetaOverlay *overlay)
                                    (overlay->current_rect.origin.y +
                                     overlay->current_rect.size.height));
 
-  overlay->previous_rect = overlay->current_rect;
-  overlay->previous_is_valid = TRUE;
+  if (!clutter_rect_equals (&overlay->previous_rect, &overlay->current_rect))
+    {
+      overlay->previous_rect = overlay->current_rect;
+      overlay->previous_is_valid = TRUE;
+    }
 }
 
 static void