Refactor root element background painting

Source/core/paint/BoxPainter.h

Index: Source/core/paint/BoxPainter.h
diff --git a/Source/core/paint/BoxPainter.h b/Source/core/paint/BoxPainter.h
index e2a1cbc96c5bde3e39c95c0e21ed2e53f80d3067..20a1aa24300837aa9d9127834d5a2b0a76fc0fcd 100644
--- a/Source/core/paint/BoxPainter.h
+++ b/Source/core/paint/BoxPainter.h
@@ -25,11 +25,12 @@ public:
     void paintBoxDecorationBackground(const PaintInfo&, const LayoutPoint&);
     void paintMask(const PaintInfo&, const LayoutPoint&);
     void paintClippingMask(const PaintInfo&, const LayoutPoint&);
-    void paintFillLayers(const PaintInfo&, const Color&, const FillLayer&, const LayoutRect&, BackgroundBleedAvoidance = BackgroundBleedNone, SkXfermode::Mode = SkXfermode::kSrcOver_Mode, LayoutObject* backgroundObject = 0);
+    bool calculateFillLayerOcclusionCulling(Vector<const FillLayer*, 8> &reversedPaintList, const FillLayer&);

[Xianzhu, 2015/06/02 23:34:35]

s/ &/& /

Is there specific reason that '8' is chosen? If not, use default.

[trchen, 2015/06/03 00:06:59]

It was there in the old paintFillLayers() code. Using the default (no on-stack
buffer) may be too inefficient since we already know at least one layer will be
added, and for most layout objects exactly one will be added.

I don't know why was 8 picked in the beginning, but allocating 64 bytes on the
stack doesn't sound like a big deal to me.

+    void paintFillLayers(const PaintInfo&, const Color&, const FillLayer&, const LayoutRect&, BackgroundBleedAvoidance = BackgroundBleedNone, SkXfermode::Mode = SkXfermode::kSrcOver_Mode, LayoutObject* backgroundObject = nullptr);
     void paintMaskImages(const PaintInfo&, const LayoutRect&);
     void paintBoxDecorationBackgroundWithRect(const PaintInfo&, const LayoutPoint&, const LayoutRect&);
-    static void paintFillLayerExtended(LayoutBoxModelObject&, const PaintInfo&, const Color&, const FillLayer&, const LayoutRect&, BackgroundBleedAvoidance, InlineFlowBox* = 0, const LayoutSize& = LayoutSize(), SkXfermode::Mode = SkXfermode::kSrcOver_Mode, LayoutObject* backgroundObject = 0, bool skipBaseColor = false);
-    static void calculateBackgroundImageGeometry(LayoutBoxModelObject&, const LayoutBoxModelObject* paintContainer, const FillLayer&, const LayoutRect& paintRect, BackgroundImageGeometry&, LayoutObject* = 0);
+    static void paintFillLayerExtended(LayoutBoxModelObject&, const PaintInfo&, const Color&, const FillLayer&, const LayoutRect&, BackgroundBleedAvoidance, InlineFlowBox* = nullptr, const LayoutSize& = LayoutSize(), SkXfermode::Mode = SkXfermode::kSrcOver_Mode, LayoutObject* backgroundObject = nullptr);
+    static void calculateBackgroundImageGeometry(LayoutBoxModelObject&, const LayoutBoxModelObject* paintContainer, const FillLayer&, const LayoutRect& paintRect, BackgroundImageGeometry&, LayoutObject* backgroundObject = nullptr);
     static InterpolationQuality chooseInterpolationQuality(LayoutObject&, GraphicsContext*, Image*, const void*, const LayoutSize&);
     static bool paintNinePieceImage(LayoutBoxModelObject&, GraphicsContext*, const LayoutRect&, const ComputedStyle&, const NinePieceImage&, SkXfermode::Mode = SkXfermode::kSrcOver_Mode);
     static void paintBorder(LayoutBoxModelObject&, const PaintInfo&, const LayoutRect&, const ComputedStyle&, BackgroundBleedAvoidance = BackgroundBleedNone, bool includeLogicalLeftEdge = true, bool includeLogicalRightEdge = true);
@@ -39,13 +40,10 @@ public:
 
 private:
     void paintBackground(const PaintInfo&, const LayoutRect&, const Color& backgroundColor, BackgroundBleedAvoidance = BackgroundBleedNone);
-    void paintRootBoxFillLayers(const PaintInfo&);
-    void paintFillLayer(const PaintInfo&, const Color&, const FillLayer&, const LayoutRect&, BackgroundBleedAvoidance, SkXfermode::Mode, LayoutObject* backgroundObject, bool skipBaseColor = false);
-    static void paintRootBackgroundColor(LayoutObject&, const PaintInfo&, const LayoutRect&, const Color&);
+    void paintFillLayer(const PaintInfo&, const Color&, const FillLayer&, const LayoutRect&, BackgroundBleedAvoidance, SkXfermode::Mode, LayoutObject* backgroundObject = nullptr);
     static FloatRoundedRect backgroundRoundedRectAdjustedForBleedAvoidance(LayoutObject&, const LayoutRect&, BackgroundBleedAvoidance, InlineFlowBox*, const LayoutSize&, bool includeLogicalLeftEdge, bool includeLogicalRightEdge);
     static FloatRoundedRect getBackgroundRoundedRect(LayoutObject&, const LayoutRect&, InlineFlowBox*, LayoutUnit inlineBoxWidth, LayoutUnit inlineBoxHeight,
         bool includeLogicalLeftEdge, bool includeLogicalRightEdge);
-    static bool isDocumentElementWithOpaqueBackground(LayoutObject&);
     static void applyBoxShadowForBackground(GraphicsContext*, LayoutObject&);
     static bool fixedBackgroundPaintsInLocalCoordinates(const LayoutObject&);
     static IntSize calculateFillTileSize(const LayoutBoxModelObject&, const FillLayer&, const IntSize& scaledPositioningAreaSize);