Don't update graphics layer positions during coordinated scrolling

Source/core/rendering/RenderLayerBacking.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 661 matching lines @@
         ASSERT(m_scrollingContentsLayer);
         RenderBox* renderBox = toRenderBox(renderer());
         IntRect clientBox = enclosingIntRect(renderBox->clientBoxRect());
         // FIXME: We should make RenderBox::clientBoxRect consider scrollbar placement.
         if (style->shouldPlaceBlockDirectionScrollbarOnLogicalLeft())
             clientBox.move(renderBox->verticalScrollbarWidth(), 0);
 
         IntSize adjustedScrollOffset = m_owningLayer->adjustedScrollOffset();
         m_scrollingLayer->setPosition(FloatPoint(clientBox.location() - localCompositingBounds.location()));
         m_scrollingLayer->setSize(clientBox.size());
-        m_scrollingContentsLayer->setPosition(FloatPoint(-adjustedScrollOffset.width(), -adjustedScrollOffset.height()));
 
         IntSize oldScrollingLayerOffset = m_scrollingLayer->offsetFromRenderer();
         m_scrollingLayer->setOffsetFromRenderer(-toIntSize(clientBox.location()));
 
         bool clientBoxOffsetChanged = oldScrollingLayerOffset != m_scrollingLayer->offsetFromRenderer();
 
         IntSize scrollSize(m_owningLayer->scrollWidth(), m_owningLayer->scrollHeight());
         if (scrollSize != m_scrollingContentsLayer->size() || clientBoxOffsetChanged)
             m_scrollingContentsLayer->setNeedsDisplay();
 
         IntSize scrollingContentsOffset = toIntSize(clientBox.location() - adjustedScrollOffset);
-        if (scrollingContentsOffset != m_scrollingContentsLayer->offsetFromRenderer() || scrollSize != m_scrollingContentsLayer->size())
-            compositor()->scrollingLayerDidChange(m_owningLayer);
+        if (scrollingContentsOffset != m_scrollingContentsLayer->offsetFromRenderer() || scrollSize != m_scrollingContentsLayer->size()) {
+            bool scrollingCoordinatorHandlesOffset = compositor()->scrollingLayerDidChange(m_owningLayer);
+
+#ifndef BLINK_SCROLLING_POSITION_NO_OFFSET

[jamesr, 2013/07/09 23:39:38]

i think you want to add something to core.gyp to set this #define sometimes,
right?

[enne (OOO), 2013/07/09 23:43:47]

I added a define here: https://codereview.chromium.org/18400003/

+            // FIXME: Remove when possible.
+            // Only required to stage multi-repo change.
+            scrollingCoordinatorHandlesOffset = false;
+#endif
+            if (scrollingCoordinatorHandlesOffset)
+                m_scrollingContentsLayer->setPosition(-m_owningLayer->scrollOrigin());
+            else
+                m_scrollingContentsLayer->setPosition(FloatPoint(-adjustedScrollOffset));
+        }
 
         m_scrollingContentsLayer->setSize(scrollSize);
         // FIXME: The paint offset and the scroll offset should really be separate concepts.
         m_scrollingContentsLayer->setOffsetFromRenderer(scrollingContentsOffset, GraphicsLayer::DontSetNeedsDisplay);
 
         if (m_foregroundLayer) {
             if (m_foregroundLayer->size() != m_scrollingContentsLayer->size())
                 m_foregroundLayer->setSize(m_scrollingContentsLayer->size());
             m_foregroundLayer->setNeedsDisplay();
             m_foregroundLayer->setOffsetFromRenderer(m_scrollingContentsLayer->offsetFromRenderer());
@@ skipping 1220 matching lines @@
     info.addMember(m_childContainmentLayer, "childContainmentLayer");
     info.addMember(m_maskLayer, "maskLayer");
     info.addMember(m_layerForHorizontalScrollbar, "layerForHorizontalScrollbar");
     info.addMember(m_layerForVerticalScrollbar, "layerForVerticalScrollbar");
     info.addMember(m_layerForScrollCorner, "layerForScrollCorner");
     info.addMember(m_scrollingLayer, "scrollingLayer");
     info.addMember(m_scrollingContentsLayer, "scrollingContentsLayer");
 }
 
 } // namespace WebCore