Invalidate scrolling contents on scrolling contents layer only

third_party/WebKit/Source/core/layout/LayoutBoxModelObject.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 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 389 matching lines @@
         layer()->compositedLayerMapping()->setContentsNeedDisplayInRect(r, invalidationReason);
     }
 }
 
 void LayoutBoxModelObject::invalidateDisplayItemClientOnBacking(const DisplayItemClientWrapper& displayItemClient, PaintInvalidationReason invalidationReason, const LayoutRect& previousPaintInvalidationRect, const LayoutRect& newPaintInvalidationRect) const
 {
     if (layer()->groupedMapping()) {
         if (GraphicsLayer* squashingLayer = layer()->groupedMapping()->squashingLayer())
             squashingLayer->invalidateDisplayItemClient(displayItemClient, invalidationReason, enclosingIntRect(previousPaintInvalidationRect), enclosingIntRect(newPaintInvalidationRect));
     } else if (CompositedLayerMapping* compositedLayerMapping = layer()->compositedLayerMapping()) {
-        compositedLayerMapping->invalidateDisplayItemClient(displayItemClient, invalidationReason, previousPaintInvalidationRect, newPaintInvalidationRect);
+        if (this->displayItemClient() != displayItemClient.displayItemClient() && isBox() && toLayoutBox(this)->usesCompositedScrolling())
+            compositedLayerMapping->invalidateDisplayItemClientOnScrollingContentsLayer(displayItemClient, invalidationReason, previousPaintInvalidationRect, newPaintInvalidationRect);

[chrishtr, 2015/10/16 00:55:38]

This conditional doesn't need to be protected by
SlimmingPaintSynchronizedPaintingEnabled? Why is it correct to not invalidate
even without the flag?

[Xianzhu, 2015/10/16 17:38:05]

A scrolling content is on the scrolling contents layer, so it's correct not to
invalidate the scrolling container layer, regardless of the flag.

Invalidating on both layers is a bug (crbug.com/416535) which is not fixed
because of crbug.com/429845 and because it is not a big issue. With this CL, we
still invalidate both layers if the invalidation is issued by the container
(while the rect may be for contents but we can't distinguish) to avoid
crbug.com/429845. If an invalidation is issued by scrolling content, we
invalidate the scrolling contents layer only.

crbug.com/416535 doesn't apply for spv2.

+        else
+            compositedLayerMapping->invalidateDisplayItemClient(displayItemClient, invalidationReason, previousPaintInvalidationRect, newPaintInvalidationRect);
     }
 }
 
 void LayoutBoxModelObject::addOutlineRectsForNormalChildren(Vector<LayoutRect>& rects, const LayoutPoint& additionalOffset, IncludeBlockVisualOverflowOrNot includeBlockOverflows) const
 {
     for (LayoutObject* child = slowFirstChild(); child; child = child->nextSibling()) {
         // Outlines of out-of-flow positioned descendants are handled in LayoutBlock::addOutlineRects().
         if (child->isOutOfFlowPositioned())
             continue;
 
@@ skipping 629 matching lines @@
     if (rootElementStyle->hasBackground())
         return false;
 
     if (node() != document().firstBodyElement())
         return false;
 
     return true;
 }
 
 } // namespace blink