Preserve fractional scroll offset for JS scrolling API

Source/core/rendering/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 875 matching lines @@
 
 void CompositedLayerMapping::updateScrollingLayerGeometry(const IntRect& localCompositingBounds)
 {
     if (!m_scrollingLayer)
         return;
 
     ASSERT(m_scrollingContentsLayer);
     RenderBox* renderBox = toRenderBox(renderer());
     IntRect clientBox = enclosingIntRect(renderBox->clientBoxRect());
 
-    IntSize adjustedScrollOffset = m_owningLayer.scrollableArea()->adjustedScrollOffset();
+    IntSize adjustedScrollOffset = flooredIntSize(m_owningLayer.scrollableArea()->adjustedScrollOffset());

[Rick Byers, 2014/10/02 21:44:06]

Add FIXME?

[Yufeng Shen (Slow to review), 2014/10/02 23:34:34]

Done.

     m_scrollingLayer->setPosition(FloatPoint(clientBox.location() - localCompositingBounds.location() + roundedIntSize(m_owningLayer.subpixelAccumulation())));
     m_scrollingLayer->setSize(clientBox.size());
 
     IntSize oldScrollingLayerOffset = m_scrollingLayer->offsetFromRenderer();
     m_scrollingLayer->setOffsetFromRenderer(-toIntSize(clientBox.location()));
 
     if (m_childClippingMaskLayer && !renderer()->style()->clipPath()) {
         m_childClippingMaskLayer->setPosition(m_scrollingLayer->position());
         m_childClippingMaskLayer->setSize(m_scrollingLayer->size());
         m_childClippingMaskLayer->setOffsetFromRenderer(toIntSize(clientBox.location()));
@@ skipping 236 matching lines @@
         m_scrollingBlockSelectionLayer->setDrawsContent(false);
         return;
     }
 
     const IntRect blockSelectionGapsBounds = m_owningLayer.blockSelectionGapsBounds();
     const bool shouldDrawContent = !blockSelectionGapsBounds.isEmpty();
     m_scrollingBlockSelectionLayer->setDrawsContent(!paintsIntoCompositedAncestor() && shouldDrawContent);
     if (!shouldDrawContent)
         return;
 
-    const IntPoint position = blockSelectionGapsBounds.location() + m_owningLayer.scrollableArea()->adjustedScrollOffset();
+    const IntPoint position = blockSelectionGapsBounds.location() + flooredIntSize(m_owningLayer.scrollableArea()->adjustedScrollOffset());

[Rick Byers, 2014/10/02 21:44:06]

add FIXME?

[Yufeng Shen (Slow to review), 2014/10/02 23:34:35]

Done.

     if (m_scrollingBlockSelectionLayer->size() == blockSelectionGapsBounds.size() && m_scrollingBlockSelectionLayer->position() == position)
         return;
 
     m_scrollingBlockSelectionLayer->setPosition(position);
     m_scrollingBlockSelectionLayer->setSize(blockSelectionGapsBounds.size());
     m_scrollingBlockSelectionLayer->setOffsetFromRenderer(toIntSize(blockSelectionGapsBounds.location()), GraphicsLayer::SetNeedsDisplay);
 }
 
 void CompositedLayerMapping::updateDrawsContent()
 {
@@ skipping 1197 matching lines @@
     } else if (graphicsLayer == m_scrollingBlockSelectionLayer.get()) {
         name = "Scrolling Block Selection Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink