Fix pixel snapping issues when layers become composited

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 32 matching lines @@
     NormalCompositingLayer, // non-tiled layer with backing store
     MediaCompositingLayer, // layer that contains an image, video, webGL or plugin
     ContainerCompositingLayer // layer with no backing store
 };
 
 
 // A GraphicsLayerPaintInfo contains all the info needed to paint a partial subtree of RenderLayers into a GraphicsLayer.
 struct GraphicsLayerPaintInfo {
     RenderLayer* renderLayer;
 
-    IntRect compositedBounds;
+    LayoutRect compositedBounds;
 
     IntSize offsetFromRenderer;
 
     GraphicsLayerPaintingPhase paintingPhase;
 
     bool isBackgroundLayer;
 };
 
 // CompositedLayerMapping keeps track of how RenderLayers of the render tree correspond to
 // GraphicsLayers of the composited layer tree. Each instance of CompositedLayerMapping
@@ skipping 73 matching lines @@
 
     // Interface to start, finish, suspend and resume animations and transitions
     bool startTransition(double, CSSPropertyID, const RenderStyle* fromStyle, const RenderStyle* toStyle);
     void transitionPaused(double timeOffset, CSSPropertyID);
     void transitionFinished(CSSPropertyID);
 
     bool startAnimation(double timeOffset, const CSSAnimationData*, const KeyframeList& keyframes);
     void animationPaused(double timeOffset, const String& name);
     void animationFinished(const String& name);
 
-    IntRect compositedBounds() const;
-    void setCompositedBounds(const IntRect&);
+    LayoutRect compositedBounds() const;
+    void setCompositedBounds(const LayoutRect&);
     void updateCompositedBounds();
 
     void updateAfterWidgetResize();
     void positionOverflowControlsLayers(const IntSize& offsetFromRoot);
     bool hasUnpositionedOverflowControlsLayers() const;
 
     // GraphicsLayerClient interface
     virtual void notifyAnimationStarted(const GraphicsLayer*, double startTime) OVERRIDE;
 
     virtual void paintContents(const GraphicsLayer*, GraphicsContext&, GraphicsLayerPaintingPhase, const IntRect& clip) OVERRIDE;
 
     virtual void didCommitChangesForLayer(const GraphicsLayer*) const OVERRIDE;
     virtual bool getCurrentTransform(const GraphicsLayer*, TransformationMatrix&) const OVERRIDE;
 
     virtual bool isTrackingRepaints() const OVERRIDE;
 
     PassOwnPtr<Vector<FloatRect> > collectTrackedRepaintRects() const;
 
 #ifndef NDEBUG
     virtual void verifyNotPainting();
 #endif
 
-    IntRect contentsBox() const;
+    LayoutRect contentsBox() const;
     IntRect backgroundBox() const;
 
     // For informative purposes only.
     CompositingLayerType compositingLayerType() const;
 
     GraphicsLayer* layerForHorizontalScrollbar() const { return m_layerForHorizontalScrollbar.get(); }
     GraphicsLayer* layerForVerticalScrollbar() const { return m_layerForVerticalScrollbar.get(); }
     GraphicsLayer* layerForScrollCorner() const { return m_layerForScrollCorner.get(); }
 
     void updateFilters(const RenderStyle*);
     bool canCompositeFilters() const { return m_canCompositeFilters; }
 
     // Return an estimate of the backing store area (in pixels) allocated by this object's GraphicsLayers.
     double backingStoreMemoryEstimate() const;
 
     void setBlendMode(BlendMode);
 
     virtual String debugName(const GraphicsLayer*) OVERRIDE;
 
+    LayoutSize subpixelAccumulation() const { return m_subpixelAccumulation; }
 private:
     void createPrimaryGraphicsLayer();
     void destroyGraphicsLayers();
 
     PassOwnPtr<GraphicsLayer> createGraphicsLayer(CompositingReasons);
 
     RenderLayerModelObject* renderer() const { return m_owningLayer->renderer(); }
     RenderLayerCompositor* compositor() const { return m_owningLayer->compositor(); }
 
     void updateInternalHierarchy();
     bool updateClippingLayers(bool needsAncestorClip, bool needsDescendantClip);
     bool updateOverflowControlsLayers(bool needsHorizontalScrollbarLayer, bool needsVerticalScrollbarLayer, bool needsScrollCornerLayer);
     bool updateForegroundLayer(bool needsForegroundLayer);
     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*);
     void updateDrawsContent(bool isSimpleContainer);
     void registerScrollingLayers();
 
+    void adjustBoundsForSubPixelAccumulation(const RenderLayer* compositedAncestor, IntRect& localCompositingBounds, IntRect& relativeCompositingBounds, IntPoint& delta);
+
     void setBackgroundLayerPaintsFixedRootBackground(bool);
 
     GraphicsLayerPaintingPhase paintingPhaseForPrimaryLayer() const;
 
-    IntSize contentOffsetInCompostingLayer() 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 updateOpacity(const RenderStyle*);
     void updateTransform(const RenderStyle*);
     void updateLayerBlendMode(const RenderStyle*);
     // Return the opacity value that this layer should use for compositing.
     float compositingOpacity(float rendererOpacity) const;
@@ skipping 90 matching lines @@
     // the background layer (or repainting).
     OwnPtr<GraphicsLayer> m_foregroundLayer; // Only used in cases where we need to draw the foreground separately.
     OwnPtr<GraphicsLayer> m_backgroundLayer; // Only used in cases where we need to draw the background separately.
 
     OwnPtr<GraphicsLayer> m_layerForHorizontalScrollbar;
     OwnPtr<GraphicsLayer> m_layerForVerticalScrollbar;
     OwnPtr<GraphicsLayer> m_layerForScrollCorner;
 
     OwnPtr<WebAnimationProvider> m_animationProvider;
 
-    IntRect m_compositedBounds;
+    LayoutRect m_compositedBounds;
+    LayoutSize m_subpixelAccumulation; // The accumulated subpixel offset of the compositedBounds compared to absolute coordinates.
 
     bool m_artificiallyInflatedBounds; // bounds had to be made non-zero to make transform-origin work
     bool m_boundsConstrainedByClipping;
     bool m_isMainFrameRenderViewLayer;
     bool m_requiresOwnBackingStoreForIntrinsicReasons;
     bool m_requiresOwnBackingStoreForAncestorReasons;
     bool m_canCompositeFilters;
     bool m_backgroundLayerPaintsFixedRootBackground;
 };
 
 } // namespace WebCore
 
 #endif // CompositedLayerMapping_h