Paint invalidation of local attachment backgrounds

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp

 /*
  * Copyright (C) 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 1240 matching lines @@
     m_childClippingMaskLayer->setSize(m_scrollingLayer->size());
     m_childClippingMaskLayer->setOffsetFromLayoutObject(
         toIntSize(overflowClipRect.location()));
   }
 
   bool overflowClipRectOffsetChanged =
       oldScrollingLayerOffset != m_scrollingLayer->offsetFromLayoutObject();
 
   IntSize scrollSize(layoutBox->pixelSnappedScrollWidth(),
                      layoutBox->pixelSnappedScrollHeight());
-  if (scrollSize != m_scrollingContentsLayer->size() ||

[chrishtr, 2016/11/17 20:42:36]

Why this change?

[Xianzhu, 2016/11/17 23:36:41]

This fully invalidated the scrolling contents layer when it's resized, which
would defeat the the new code in BoxPaintInvalidator.

-      overflowClipRectOffsetChanged)
+  if (overflowClipRectOffsetChanged)
     m_scrollingContentsLayer->setNeedsDisplay();
 
   DoubleSize scrollingContentsOffset(
       overflowClipRect.location().x() - scrollPosition.x(),
       overflowClipRect.location().y() - scrollPosition.y());
   // The scroll offset change is compared using floating point so that
   // fractional scroll offset change can be propagated to compositor.
   if (scrollingContentsOffset != m_scrollingContentsOffset ||
       scrollSize != m_scrollingContentsLayer->size()) {
     bool coordinatorHandlesOffset =
@@ skipping 1978 matching lines @@
   } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
     name = "Scrolling Contents Layer";
   } else {
     ASSERT_NOT_REACHED();
   }
 
   return name;
 }
 
 }  // namespace blink