Drop background color optimization for composited layers

Source/core/rendering/CompositedLayerMapping.h

 /*
  * 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 215 matching lines @@
     bool updateBackgroundLayer(bool needsBackgroundLayer);
     bool updateMaskLayer(bool needsMaskLayer);
     bool updateClippingMaskLayers(bool needsChildClippingMaskLayer);
     bool requiresHorizontalScrollbarLayer() const { return m_owningLayer->scrollableArea() && m_owningLayer->scrollableArea()->horizontalScrollbar(); }
     bool requiresVerticalScrollbarLayer() const { return m_owningLayer->scrollableArea() && m_owningLayer->scrollableArea()->verticalScrollbar(); }
     bool requiresScrollCornerLayer() const { return m_owningLayer->scrollableArea() && !m_owningLayer->scrollableArea()->scrollCornerAndResizerRect().isEmpty(); }
     bool updateScrollingLayers(bool scrollingLayers);
     void updateScrollParent(RenderLayer*);
     void updateClipParent(RenderLayer*);
     bool updateSquashingLayers(bool needsSquashingLayers);
-    void updateDrawsContent(bool isSimpleContainer);
+    void updateDrawsContent();
     void updateChildrenTransform();
     void registerScrollingLayers();
 
     void adjustBoundsForSubPixelAccumulation(const RenderLayer* compositedAncestor, IntRect& localCompositingBounds, IntRect& relativeCompositingBounds, IntPoint& delta);
 
     void setBackgroundLayerPaintsFixedRootBackground(bool);
 
     GraphicsLayerPaintingPhase paintingPhaseForPrimaryLayer() const;
 
     LayoutSize contentOffsetInCompostingLayer() const;
     // Result is transform origin in pixels.
     FloatPoint3D computeTransformOrigin(const IntRect& borderBox) const;
     // Result is perspective origin in pixels.
     FloatPoint computePerspectiveOrigin(const IntRect& borderBox) const;
 
     void updateSquashingLayerGeometry(const IntPoint& delta);
 
     void updateOpacity(const RenderStyle*);
     void updateTransform(const RenderStyle*);
     void updateLayerBlendMode(const RenderStyle*);
     void updateIsRootForIsolatedGroup();
     // Return the opacity value that this layer should use for compositing.
     float compositingOpacity(float rendererOpacity) const;
 
     bool isMainFrameRenderViewLayer() const;
 
-    bool paintsBoxDecorations() const;
     bool paintsChildren() const;
 
-    // Returns true if this compositing layer has no visible content.
-    bool isSimpleContainerCompositingLayer() const;
     // Returns true if this layer has content that needs to be rendered by painting into the backing store.
-    bool containsPaintedContent(bool isSimpleContainer) const;
+    bool containsPaintedContent() const;
+    bool paintsIntoOwningLayer() const;

[alokp, 2014/02/26 22:11:16]

I do not understand what this function is returning. Who paints into owning
layer? Please add a comment.

     // Returns true if the RenderLayer just contains an image that we can composite directly.
     bool isDirectlyCompositedImage() const;
     void updateImageContents();
 
     Color rendererBackgroundColor() const;
-    void updateBackgroundColor(bool isSimpleContainer);
-    void updateContentsRect(bool isSimpleContainer);
+    void updateBackgroundColor();
+    void updateContentsRect();
 
     void updateCompositingReasons();
 
     bool hasVisibleNonCompositingDescendantLayers() const;
 
     bool shouldClipCompositedBounds() const;
 
     void paintsIntoCompositedAncestorChanged();
 
     void doPaintTask(GraphicsLayerPaintInfo&, GraphicsContext*, const IntRect& clip);
@@ skipping 80 matching lines @@
     bool m_isMainFrameRenderViewLayer;
     bool m_requiresOwnBackingStoreForIntrinsicReasons;
     bool m_requiresOwnBackingStoreForAncestorReasons;
     bool m_canCompositeFilters;
     bool m_backgroundLayerPaintsFixedRootBackground;
 };
 
 } // namespace WebCore
 
 #endif // CompositedLayerMapping_h