Anti-aliased box borders (overdraw)

Source/core/paint/BoxBorderPainter.h

Index: Source/core/paint/BoxBorderPainter.h
diff --git a/Source/core/paint/BoxBorderPainter.h b/Source/core/paint/BoxBorderPainter.h
new file mode 100644
index 0000000000000000000000000000000000000000..21af6d97084823ce95e62b7536e22b07b813a790
--- /dev/null
+++ b/Source/core/paint/BoxBorderPainter.h
@@ -0,0 +1,80 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BoxBorderPainter_h
+#define BoxBorderPainter_h
+
+#include "core/layout/LayoutBoxModelObject.h"
+#include "core/style/BorderEdge.h"
+
+namespace blink {
+
+enum BorderEdgeFlag {
+    TopBorderEdge = 1 << BSTop,
+    RightBorderEdge = 1 << BSRight,
+    BottomBorderEdge = 1 << BSBottom,
+    LeftBorderEdge = 1 << BSLeft,
+    AllBorderEdges = TopBorderEdge | BottomBorderEdge | LeftBorderEdge | RightBorderEdge
+};
+
+struct BoxBorderInfo {
+    STACK_ALLOCATED();
+public:
+    BoxBorderInfo(const ComputedStyle&, BackgroundBleedAvoidance,
+        bool includeLogicalLeftEdge, bool includeLogicalRightEdge);
+
+    const ComputedStyle& style;
+    const BackgroundBleedAvoidance bleedAvoidance;
+    const bool includeLogicalLeftEdge;
+    const bool includeLogicalRightEdge;
+
+    BorderEdge edges[4];
+
+    unsigned visibleEdgeCount;
+    unsigned firstVisibleEdge;
+    BorderEdgeFlags visibleEdgeSet;
+
+    bool isUniformStyle;
+    bool isUniformWidth;
+    bool isUniformColor;
+    bool hasAlpha;
+};
+
+class BoxBorderPainter {
+    STACK_ALLOCATED();
+public:
+    BoxBorderPainter(const BoxBorderInfo&, const FloatRoundedRect& outer,
+        const FloatRoundedRect& inner);
+
+    void paint(GraphicsContext*) const;
+
+private:
+    struct OpacityGroup {
+        Vector<BoxSide, 4> sides;
+        BorderEdgeFlags edgeFlags;
+        unsigned alpha;
+    };
+
+    enum MitreType { NoMitre, AntiAliasedMitre, NonAntiAliasedMitre };
+
+    MitreType computeMitre(BoxSide, BoxSide adjacentSide, BorderEdgeFlags paintedSides) const;
+    bool colorNeedsAntiAliasAtCorner(BoxSide, BoxSide adjacentSide, Color) const;
+    void paintSide(GraphicsContext*, BoxSide, unsigned alpha, BorderEdgeFlags paintedSides) const;
+
+    BorderEdgeFlags paintGroup(GraphicsContext*, unsigned index, float opacity) const;
+    void clipBorderSidePolygon(GraphicsContext*, BoxSide, MitreType mitre1, MitreType mitre2) const;
+
+    const BoxBorderInfo& m_borderInfo;
+    const FloatRoundedRect& m_outer;
+    const FloatRoundedRect& m_inner;
+
+    Path m_roundedPath;
+    Vector<OpacityGroup, 4> m_opacityGroups;
+    Vector<size_t, 4> m_opacityGroupIndices;
+    bool m_hasRadii[4]; // TopLeft, TopRight, BottomRight, BottomLeft
+};
+
+} // namespace blink
+
+#endif