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

Source/core/page/scrolling/ScrollingCoordinator.cpp

Index: Source/core/page/scrolling/ScrollingCoordinator.cpp
diff --git a/Source/core/page/scrolling/ScrollingCoordinator.cpp b/Source/core/page/scrolling/ScrollingCoordinator.cpp
index c3e5612689532ef98719d7440df328ebf2a8041b..096f44ea7001182011306cd0fe52e414573ee898 100644
--- a/Source/core/page/scrolling/ScrollingCoordinator.cpp
+++ b/Source/core/page/scrolling/ScrollingCoordinator.cpp
@@ -447,6 +447,13 @@ static void projectRectsToGraphicsLayerSpaceRecursive(
         } 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();