Offset rects by origin when projecting from composited to graphics layer.

Source/core/page/scrolling/ScrollingCoordinator.cpp

 /*
  * Copyright (C) 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 429 matching lines @@
 
         // Find the appropriate GraphicsLayer for the composited RenderLayer.
         GraphicsLayer* graphicsLayer;
         LayoutSize extraOffset;
         if (compositedLayer->compositingState() == PaintsIntoGroupedBacking) {
             graphicsLayer = compositedLayer->groupedMapping()->squashingLayer();
             extraOffset = -compositedLayer->offsetFromSquashingLayerOrigin();
         } else {
             ASSERT(compositedLayer->hasCompositedLayerMapping());
             CompositedLayerMappingPtr compositedLayerMapping = compositedLayer->compositedLayerMapping();
+            // The origin for the graphics layer does not have to be the same
+            // as the composited layer (e.g. when a child layer has negative
+            // offset and paints into this layer), so when projecting rects to
+            // graphics layer space they have to be offset by the origin for
+            // the composited layer.
+            LayoutPoint graphicsLayerOffset  = compositedLayerMapping->compositedBounds().location();

[Ian Vollick, 2014/04/23 20:18:38]

It sounds like you want exactly
CompositedLayerMapping::contentOffsetInCompositingLayer. Perhaps this can be
made public.

[Zeeshan Qureshi, 2014/04/24 02:32:40]

Excellent idea, done.

+            extraOffset = LayoutSize(-graphicsLayerOffset.x(), -graphicsLayerOffset.y());
             // If the layer is using composited scrolling, then it's the contents that these
             // rects apply to.
             graphicsLayer = compositedLayerMapping->scrollingContentsLayer();
             if (!graphicsLayer)
                 graphicsLayer = compositedLayerMapping->mainGraphicsLayer();
         }
 
         GraphicsLayerHitTestRects::iterator glIter = graphicsRects.find(graphicsLayer);
         Vector<LayoutRect>* glRects;
         if (glIter == graphicsRects.end())
@@ skipping 505 matching lines @@
     bool frameIsScrollable = frameView && frameView->isScrollable();
     if (frameIsScrollable != m_wasFrameScrollable)
         return true;
 
     if (WebLayer* scrollLayer = frameView ? toWebLayer(frameView->layerForScrolling()) : 0)
         return blink::WebSize(frameView->contentsSize()) != scrollLayer->bounds();
     return false;
 }
 
 } // namespace WebCore