[mutter/gnome-3-28] clutter: Avoid rounding compensation when invalidating 2D actors

[Marco Trevisan <marcotrevi src gnome org>]

commit 56a4f33da0484778a9254e67e34cc32736585254
Author: Carlos Garnacho <carlosg gnome org>
Date:   Fri May 5 12:15:30 2017 +0000

    clutter: Avoid rounding compensation when invalidating 2D actors
    
    This allows the redraw clip to be more constrained, so MetaCullable doesn't
    end up rendering portions of window shadows, frame and background when a
    window invalidates (part of) its contents.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=782344
    
    
    (cherry picked from commit a7df459416dc46321204c98197e4fd84724976e0)

 clutter/clutter/clutter-paint-volume.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)
---
diff --git a/clutter/clutter/clutter-paint-volume.c b/clutter/clutter/clutter-paint-volume.c
index b48f7f9d6..f3405138b 100644
--- a/clutter/clutter/clutter-paint-volume.c
+++ b/clutter/clutter/clutter-paint-volume.c
@@ -1166,6 +1166,21 @@ _clutter_paint_volume_get_stage_paint_box (ClutterPaintVolume *pv,
 
   _clutter_paint_volume_get_bounding_box (&projected_pv, box);
 
+  if (pv->is_2d && pv->actor &&
+      clutter_actor_get_z_position (pv->actor) == 0)
+    {
+      /* If the volume/actor are perfectly 2D, take the bounding box as
+       * good. We won't need to add any extra room for sub-pixel positioning
+       * in this case.
+       */
+      clutter_paint_volume_free (&projected_pv);
+      box->x1 = CLUTTER_NEARBYINT (box->x1);
+      box->y1 = CLUTTER_NEARBYINT (box->y1);
+      box->x2 = CLUTTER_NEARBYINT (box->x2);
+      box->y2 = CLUTTER_NEARBYINT (box->y2);
+      return;
+    }
+
   /* The aim here is that for a given rectangle defined with floating point
    * coordinates we want to determine a stable quantized size in pixels
    * that doesn't vary due to the original box's sub-pixel position.