Highlighting on UAOS - alternate approach

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 1043 matching lines @@
 void CompositedLayerMapping::updateDrawsContent()
 {
     if (m_scrollingLayer) {
         // We don't have to consider overflow controls, because we know that the scrollbars are drawn elsewhere.
         // m_graphicsLayer only needs backing store if the non-scrolling parts (background, outlines, borders, shadows etc) need to paint.
         // m_scrollingLayer never has backing store.
         // m_scrollingContentsLayer only needs backing store if the scrolled contents need to paint.
         bool hasNonScrollingPaintedContent = m_owningLayer.hasVisibleContent() && m_owningLayer.hasBoxDecorationsOrBackground();
         m_graphicsLayer->setDrawsContent(hasNonScrollingPaintedContent);
 
-        bool hasScrollingPaintedContent = m_owningLayer.hasVisibleContent() && (renderer()->hasBackground() || paintsChildren());
+        bool hasScrollingPaintedContent = m_owningLayer.hasVisibleContent() && (renderer()->hasBackground() || paintsChildren() || hasScrollChildren());
         m_scrollingContentsLayer->setDrawsContent(hasScrollingPaintedContent);
         return;
     }
 
     bool hasPaintedContent = containsPaintedContent();
     if (hasPaintedContent && isAcceleratedCanvas(renderer())) {
         CanvasRenderingContext* context = toHTMLCanvasElement(renderer()->node())->renderingContext();
         // Content layer may be null if context is lost.
         if (blink::WebLayer* contentLayer = context->platformLayer()) {
             Color bgColor(Color::transparent);
@@ skipping 400 matching lines @@
 void CompositedLayerMapping::updateScrollParent(RenderLayer* scrollParent)
 {
     if (ScrollingCoordinator* scrollingCoordinator = scrollingCoordinatorFromLayer(m_owningLayer)) {
         GraphicsLayer* topmostLayer = childForSuperlayers();
         updateScrollParentForGraphicsLayer(m_squashingContainmentLayer.get(), topmostLayer, scrollParent, scrollingCoordinator);
         updateScrollParentForGraphicsLayer(m_ancestorClippingLayer.get(), topmostLayer, scrollParent, scrollingCoordinator);
         updateScrollParentForGraphicsLayer(m_graphicsLayer.get(), topmostLayer, scrollParent, scrollingCoordinator);
     }
 }
 
+bool CompositedLayerMapping::hasScrollChildren()
+{
+    ScrollingCoordinator* scrollingCoordinator = scrollingCoordinatorFromLayer(m_owningLayer);
+    if (!scrollingCoordinator)
+        return false;
+    return scrollingCoordinator->hasScrollChildren(parentForSublayers());
+}
+
 void CompositedLayerMapping::updateClipParent(RenderLayer* clipParent)
 {
     if (ScrollingCoordinator* scrollingCoordinator = scrollingCoordinatorFromLayer(m_owningLayer))
         scrollingCoordinator->updateClipParentForGraphicsLayer(m_graphicsLayer.get(), clipParent);
 }
 
 bool CompositedLayerMapping::updateSquashingLayers(bool needsSquashingLayers)
 {
     bool layersChanged = false;
 
@@ skipping 751 matching lines @@
     } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
         name = "Scrolling Contents Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore