Fix pixel snapping issues when layers become composited

Source/core/rendering/RenderLayer.h

 /*
  * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 597 matching lines @@
     // paints the layers that intersect the damage rect from back to
     // front.  The hitTest method looks for mouse events by walking
     // layers that intersect the point from front to back.
     void paint(GraphicsContext*, const LayoutRect& damageRect, PaintBehavior = PaintBehaviorNormal, RenderObject* paintingRoot = 0,
         RenderRegion* = 0, PaintLayerFlags = 0);
     bool hitTest(const HitTestRequest&, HitTestResult&);
     bool hitTest(const HitTestRequest&, const HitTestLocation&, HitTestResult&);
     void paintOverlayScrollbars(GraphicsContext*, const LayoutRect& damageRect, PaintBehavior, RenderObject* paintingRoot = 0);
 
     struct ClipRectsContext {
-        ClipRectsContext(const RenderLayer* inRootLayer, RenderRegion* inRegion, ClipRectsType inClipRectsType, OverlayScrollbarSizeRelevancy inOverlayScrollbarSizeRelevancy = IgnoreOverlayScrollbarSize, ShouldRespectOverflowClip inRespectOverflowClip = RespectOverflowClip)
+        ClipRectsContext(const RenderLayer* inRootLayer, RenderRegion* inRegion, ClipRectsType inClipRectsType,
+            OverlayScrollbarSizeRelevancy inOverlayScrollbarSizeRelevancy = IgnoreOverlayScrollbarSize,
+            ShouldRespectOverflowClip inRespectOverflowClip = RespectOverflowClip, const LayoutSize& inSubPixelAccumulation = LayoutSize())
             : rootLayer(inRootLayer)
             , region(inRegion)
             , clipRectsType(inClipRectsType)
             , overlayScrollbarSizeRelevancy(inOverlayScrollbarSizeRelevancy)
             , respectOverflowClip(inRespectOverflowClip)
+            , subPixelAccumulation(inSubPixelAccumulation)
         { }
         const RenderLayer* rootLayer;
         RenderRegion* region;
         ClipRectsType clipRectsType;
         OverlayScrollbarSizeRelevancy overlayScrollbarSizeRelevancy;
         ShouldRespectOverflowClip respectOverflowClip;
+        const LayoutSize& subPixelAccumulation;
     };
 
     // This method figures out our layerBounds in coordinates relative to
     // |rootLayer}.  It also computes our background and foreground clip rects
     // for painting/event handling.
     // Pass offsetFromRoot if known.
     void calculateRects(const ClipRectsContext&, const LayoutRect& paintDirtyRect, LayoutRect& layerBounds,
         ClipRect& backgroundRect, ClipRect& foregroundRect, ClipRect& outlineRect, const LayoutPoint* offsetFromRoot = 0) const;
 
     // Compute and cache clip rects computed with the given layer as the root
@@ skipping 35 matching lines @@
     IntRect absoluteBoundingBox() const;
 
     // Bounds used for layer overlap testing in RenderLayerCompositor.
     LayoutRect overlapBounds() const { return overlapBoundsIncludeChildren() ? calculateLayerBounds(this) : localBoundingBox(); }
 
     // If true, this layer's children are included in its bounds for overlap testing.
     // We can't rely on the children's positions if this layer has a filter that could have moved the children's pixels around.
     bool overlapBoundsIncludeChildren() const { return hasFilter() && renderer()->style()->filter().hasFilterThatMovesPixels(); }
 
     // Can pass offsetFromRoot if known.
-    IntRect calculateLayerBounds(const RenderLayer* ancestorLayer, const LayoutPoint* offsetFromRoot = 0, CalculateLayerBoundsFlags = DefaultCalculateLayerBoundsFlags) const;
+    LayoutRect calculateLayerBounds(const RenderLayer* ancestorLayer, const LayoutPoint* offsetFromRoot = 0, CalculateLayerBoundsFlags = DefaultCalculateLayerBoundsFlags) const;
 
     // WARNING: This method returns the offset for the parent as this is what updateLayerPositions expects.
     LayoutPoint computeOffsetFromRoot(bool& hasLayerOffset) const;
 
     // Return a cached repaint rect, computed relative to the layer renderer's containerForRepaint.
     LayoutRect repaintRect() const { return m_repaintRect; }
     LayoutRect repaintRectIncludingNonCompositingDescendants() const;
 
     void setRepaintStatus(RepaintStatus status) { m_repaintStatus = status; }
 
@@ skipping 245 matching lines @@
     void paintLayer(GraphicsContext*, const LayerPaintingInfo&, PaintLayerFlags);
     void paintLayerContentsAndReflection(GraphicsContext*, const LayerPaintingInfo&, PaintLayerFlags);
     void paintLayerByApplyingTransform(GraphicsContext*, const LayerPaintingInfo&, PaintLayerFlags, const LayoutPoint& translationOffset = LayoutPoint());
     void paintLayerContents(GraphicsContext*, const LayerPaintingInfo&, PaintLayerFlags);
     void paintList(Vector<RenderLayer*>*, GraphicsContext*, const LayerPaintingInfo&, PaintLayerFlags);
     void paintPaginatedChildLayer(RenderLayer* childLayer, GraphicsContext*, const LayerPaintingInfo&, PaintLayerFlags);
     void paintChildLayerIntoColumns(RenderLayer* childLayer, GraphicsContext*, const LayerPaintingInfo&, PaintLayerFlags, const Vector<RenderLayer*>& columnLayers, size_t columnIndex);
 
     void collectFragments(LayerFragments&, const RenderLayer* rootLayer, RenderRegion*, const LayoutRect& dirtyRect,
         ClipRectsType, OverlayScrollbarSizeRelevancy inOverlayScrollbarSizeRelevancy = IgnoreOverlayScrollbarSize,
-        ShouldRespectOverflowClip = RespectOverflowClip, const LayoutPoint* offsetFromRoot = 0, const LayoutRect* layerBoundingBox = 0);
+        ShouldRespectOverflowClip = RespectOverflowClip, const LayoutPoint* offsetFromRoot = 0,
+        const LayoutSize& subPixelAccumulation = LayoutSize(), const LayoutRect* layerBoundingBox = 0);
     void updatePaintingInfoForFragments(LayerFragments&, const LayerPaintingInfo&, PaintLayerFlags, bool shouldPaintContent, const LayoutPoint* offsetFromRoot);
     void paintBackgroundForFragments(const LayerFragments&, GraphicsContext*, GraphicsContext* transparencyLayerContext,
         const LayoutRect& transparencyPaintDirtyRect, bool haveTransparency, const LayerPaintingInfo&, PaintBehavior, RenderObject* paintingRootForRenderer);
     void paintForegroundForFragments(const LayerFragments&, GraphicsContext*, GraphicsContext* transparencyLayerContext,
         const LayoutRect& transparencyPaintDirtyRect, bool haveTransparency, const LayerPaintingInfo&, PaintBehavior, RenderObject* paintingRootForRenderer,
         bool selectionOnly, bool forceBlackText);
     void paintForegroundForFragmentsWithPhase(PaintPhase, const LayerFragments&, GraphicsContext*, const LayerPaintingInfo&, PaintBehavior, RenderObject* paintingRootForRenderer);
     void paintOutlineForFragments(const LayerFragments&, GraphicsContext*, const LayerPaintingInfo&, PaintBehavior, RenderObject* paintingRootForRenderer);
     void paintOverflowControlsForFragments(const LayerFragments&, GraphicsContext*, const LayerPaintingInfo&);
     void paintMaskForFragments(const LayerFragments&, GraphicsContext*, const LayerPaintingInfo&, RenderObject* paintingRootForRenderer);
@@ skipping 378 matching lines @@
 
 } // namespace WebCore
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showLayerTree(const WebCore::RenderLayer*);
 void showLayerTree(const WebCore::RenderObject*);
 #endif
 
 #endif // RenderLayer_h