[mutter/wip/carlosg/performance-improvements: 34/38] compositor: Ensure to clip partial shadow redraws

[Carlos Garnacho <carlosg src gnome org>]

commit fa8e4f60f66019e9bbaa2b75ee5bc6257979ce1f
Author: Carlos Garnacho <carlosg gnome org>
Date:   Sat May 6 17:34:56 2017 +0200

    compositor: Ensure to clip partial shadow redraws
    
    Otherwise we end up drawing too far outside the clip area, which
    brings in artifacts now that we have tighter regions instead of
    an overlapping rect.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=782344

 src/compositor/meta-window-actor.c |   14 +++++++++++++-
 1 files changed, 13 insertions(+), 1 deletions(-)
---
diff --git a/src/compositor/meta-window-actor.c b/src/compositor/meta-window-actor.c
index 69d39c8..3dd9d46 100644
--- a/src/compositor/meta-window-actor.c
+++ b/src/compositor/meta-window-actor.c
@@ -715,6 +715,7 @@ meta_window_actor_paint (ClutterActor *actor)
       cairo_rectangle_int_t shape_bounds;
       cairo_region_t *clip = priv->shadow_clip;
       MetaWindow *window = priv->window;
+      gboolean partially_drawn = FALSE;
 
       meta_window_actor_get_shape_bounds (self, &shape_bounds);
       meta_window_actor_get_shadow_params (self, appears_focused, &params);
@@ -732,6 +733,17 @@ meta_window_actor_paint (ClutterActor *actor)
 
           cairo_region_subtract (clip, frame_bounds);
         }
+      else if (clip)
+        {
+          cairo_rectangle_int_t shadow_bounds;
+          cairo_region_t *shadow_region;
+
+          meta_window_actor_get_shadow_bounds (self, appears_focused, &shadow_bounds);
+          shadow_region = cairo_region_create_rectangle (&shadow_bounds);
+          cairo_region_intersect (shadow_region, clip);
+          partially_drawn = !cairo_region_is_empty (shadow_region);
+          cairo_region_destroy (shadow_region);
+        }
 
       meta_shadow_paint (shadow,
                          params.x_offset + shape_bounds.x,
@@ -740,7 +752,7 @@ meta_window_actor_paint (ClutterActor *actor)
                          shape_bounds.height,
                          (clutter_actor_get_paint_opacity (actor) * params.opacity * window->opacity) / (255 
* 255),
                          clip,
-                         clip_shadow_under_window (self)); /* clip_strictly - not just as an optimization */
+                         clip_shadow_under_window (self) || partially_drawn);
 
       if (clip && clip != priv->shadow_clip)
         cairo_region_destroy (clip);