Should not repaint if a CSS property change can be composited

Source/core/rendering/RenderLayerModelObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010, 2012 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 93 matching lines @@
                 if (oldStyle->clip() != newStyle->clip())
                     layer()->clipper().clearClipRectsIncludingDescendants();
             } else if (diff == StyleDifferenceRepaint || newStyle->outlineSize() < oldStyle->outlineSize())
                 repaint();
         }
 
         if (diff == StyleDifferenceLayout || diff == StyleDifferenceSimplifiedLayout) {
             // When a layout hint happens, we go ahead and do a repaint of the layer, since the layer could
             // end up being destroyed.
             if (hasLayer()) {
-                if (oldStyle->position() != newStyle->position()
-                    || oldStyle->zIndex() != newStyle->zIndex()
-                    || oldStyle->hasAutoZIndex() != newStyle->hasAutoZIndex()
-                    || !(oldStyle->clip() == newStyle->clip())
-                    || oldStyle->hasClip() != newStyle->hasClip()
-                    || oldStyle->opacity() != newStyle->opacity()
-                    || oldStyle->transform() != newStyle->transform()
-                    || oldStyle->filter() != newStyle->filter()
-                    )
-                layer()->repainter().repaintIncludingDescendants();
+                if (oldStyle->hasClip() != newStyle->hasClip()
+                    || oldStyle->clip() != newStyle->clip()) {
+                    // Composited layers don't need to be repainted when a parent's clip changes.
+                    layer()->repainter().repaintIncludingNonCompositingDescendants(this);
+                } else if (!layer()->hasCompositedLayerMapping()) {
+                    if (oldStyle->position() != newStyle->position()
+                        || oldStyle->zIndex() != newStyle->zIndex()
+                        || oldStyle->hasAutoZIndex() != newStyle->hasAutoZIndex()
+                        || oldStyle->opacity() != newStyle->opacity()
+                        || oldStyle->transform() != newStyle->transform()
+                        || oldStyle->filter() != newStyle->filter())
+                    layer()->repainter().repaintIncludingDescendants();
+                }
             } else if (newStyle->hasTransform() || newStyle->opacity() < 1 || newStyle->hasFilter()) {
                 // If we don't have a layer yet, but we are going to get one because of transform or opacity,
                 //  then we need to repaint the old position of the object.
                 repaint();
             }
         }
     }
 
     RenderObject::styleWillChange(diff, newStyle);
 }
@@ skipping 80 matching lines @@
     return m_layer ? m_layer->hasCompositedLayerMapping() : false;
 }
 
 CompositedLayerMapping* RenderLayerModelObject::groupedMapping() const
 {
     return m_layer ? m_layer->groupedMapping() : 0;
 }
 
 } // namespace WebCore