Paint local attachment backgrounds into composited scrolling contents layer

third_party/WebKit/Source/core/layout/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 291 matching lines @@
         if (!context->hasAlpha())
             m_graphicsLayer->setContentsOpaque(true);
         else if (WebLayer* layer = context->platformLayer())
             m_graphicsLayer->setContentsOpaque(!Color(layer->backgroundColor()).hasAlpha());
         else
             m_graphicsLayer->setContentsOpaque(false);
     } else if (m_backgroundLayer) {
         m_graphicsLayer->setContentsOpaque(false);
         m_backgroundLayer->setContentsOpaque(m_owningLayer.backgroundIsKnownToBeOpaqueInRect(compositedBounds()));
     } else {
-        // For non-root layers, background is always painted by the primary graphics layer.
+        // For non-root layers, background is painted by the scrolling contents layer if all backgrounds
+        // are background attachment local, otherwise background is painted by the primary graphics layer.
+        if (hasScrollingLayer() && m_owningLayer.shouldPaintBackgroundOntoForeground()) {
+            // Backgrounds painted onto the foreground are clipped by the padding box rect.
+            // TODO(flackr): Check the entire overflow rect.
+            m_scrollingContentsLayer->setContentsOpaque(m_owningLayer.backgroundIsKnownToBeOpaqueInRect(toLayoutBox(layoutObject())->paddingBoxRect()));
+        }
+        // The border is always painted by the m_graphicsLayer, so we check if it is known to be
+        // opaque separately.
         m_graphicsLayer->setContentsOpaque(m_owningLayer.backgroundIsKnownToBeOpaqueInRect(compositedBounds()));
     }
 }
 
 void CompositedLayerMapping::updateCompositedBounds()
 {
     ASSERT(m_owningLayer.compositor()->lifecycle().state() == DocumentLifecycle::InCompositingUpdate);
     // FIXME: if this is really needed for performance, it would be better to store it on Layer.
     m_compositedBounds = m_owningLayer.boundingBoxForCompositing();
     m_contentOffsetInCompositingLayerDirty = true;
@@ skipping 2091 matching lines @@
     if (graphicsLayerPaintingPhase & GraphicsLayerPaintBackground)
         paintLayerFlags |= PaintLayerPaintingCompositingBackgroundPhase;
     if (graphicsLayerPaintingPhase & GraphicsLayerPaintForeground)
         paintLayerFlags |= PaintLayerPaintingCompositingForegroundPhase;
     if (graphicsLayerPaintingPhase & GraphicsLayerPaintMask)
         paintLayerFlags |= PaintLayerPaintingCompositingMaskPhase;
     if (graphicsLayerPaintingPhase & GraphicsLayerPaintChildClippingMask)
         paintLayerFlags |= PaintLayerPaintingChildClippingMaskPhase;
     if (graphicsLayerPaintingPhase & GraphicsLayerPaintOverflowContents)
         paintLayerFlags |= PaintLayerPaintingOverflowContents;
-    if (graphicsLayerPaintingPhase & GraphicsLayerPaintCompositedScroll)
+    if (graphicsLayerPaintingPhase & GraphicsLayerPaintCompositedScroll) {
         paintLayerFlags |= PaintLayerPaintingCompositingScrollingPhase;
+        if (m_owningLayer.shouldPaintBackgroundOntoForeground())
+            paintLayerFlags |= PaintLayerPaintingBackgroundOntoForeground;
+    }
 
     if (graphicsLayer == m_backgroundLayer.get())
         paintLayerFlags |= (PaintLayerPaintingRootBackgroundOnly | PaintLayerPaintingCompositingForegroundPhase); // Need PaintLayerPaintingCompositingForegroundPhase to walk child layers.
     else if (compositor()->fixedRootBackgroundLayer())
         paintLayerFlags |= PaintLayerPaintingSkipRootBackground;
 
     if (graphicsLayer == m_graphicsLayer.get()
         || graphicsLayer == m_foregroundLayer.get()
         || graphicsLayer == m_backgroundLayer.get()
         || graphicsLayer == m_maskLayer.get()
@@ skipping 224 matching lines @@
     } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
         name = "Scrolling Contents Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink