Make SVG painting independent of GraphicsContext's alpha state

Source/platform/graphics/GraphicsContext.h

 /*
  * Copyright (C) 2003, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2008-2009 Torch Mobile, Inc.
  * Copyright (C) 2013 Google 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.
@@ skipping 102 matching lines @@
     void setStrokeThickness(float thickness) { mutableState()->setStrokeThickness(thickness); }
 
     StrokeStyle strokeStyle() const { return immutableState()->strokeData().style(); }
     void setStrokeStyle(StrokeStyle style) { mutableState()->setStrokeStyle(style); }
 
     Color strokeColor() const { return immutableState()->strokeColor(); }
     void setStrokeColor(const Color& color) { mutableState()->setStrokeColor(color); }
     SkColor effectiveStrokeColor() const { return immutableState()->effectiveStrokeColor(); }
 
     Pattern* strokePattern() const { return immutableState()->strokePattern(); }
-    void setStrokePattern(PassRefPtr<Pattern>);
+    void setStrokePattern(PassRefPtr<Pattern>, float additionalAlpha = 1);
 
     Gradient* strokeGradient() const { return immutableState()->strokeGradient(); }
-    void setStrokeGradient(PassRefPtr<Gradient>);
+    void setStrokeGradient(PassRefPtr<Gradient>, float additionalAlpha = 1);
 
     void setLineCap(LineCap cap) { mutableState()->setLineCap(cap); }
     void setLineDash(const DashArray& dashes, float dashOffset) { mutableState()->setLineDash(dashes, dashOffset); }
     void setLineJoin(LineJoin join) { mutableState()->setLineJoin(join); }
     void setMiterLimit(float limit) { mutableState()->setMiterLimit(limit); }
 
     WindRule fillRule() const { return immutableState()->fillRule(); }
     void setFillRule(WindRule fillRule) { mutableState()->setFillRule(fillRule); }
 
     Color fillColor() const { return immutableState()->fillColor(); }
     void setFillColor(const Color& color) { mutableState()->setFillColor(color); }
     SkColor effectiveFillColor() const { return immutableState()->effectiveFillColor(); }
 
-    void setFillPattern(PassRefPtr<Pattern>);
+    void setFillPattern(PassRefPtr<Pattern>, float additionalAlpha = 1);
     Pattern* fillPattern() const { return immutableState()->fillPattern(); }
 
-    void setFillGradient(PassRefPtr<Gradient>);
+    void setFillGradient(PassRefPtr<Gradient>, float additionalAlpha = 1);
     Gradient* fillGradient() const { return immutableState()->fillGradient(); }
 
     SkDrawLooper* drawLooper() const { return immutableState()->drawLooper(); }
 
     bool getTransformedClipBounds(FloatRect* bounds) const;
     SkMatrix getTotalMatrix() const;
 
     void setShouldAntialias(bool antialias) { mutableState()->setShouldAntialias(antialias); }
     bool shouldAntialias() const { return immutableState()->shouldAntialias(); }
 
@@ skipping 235 matching lines @@
         return focusRingOutset(offset) + (focusRingWidth(width) + 1) / 2;
     }
 
     // public decl needed for OwnPtr wrapper.
     class RecordingState;
 
 #if ENABLE(ASSERT)
     void setInDrawingRecorder(bool);
 #endif
 
+    // Multiply a color's alpha channel by an additional alpha factor. This is
+    // similar to Color::combineWithAlpha but uses Skia's rounding approach.
+    static SkColor combineWithAlpha(SkColor color, float alpha)
+    {
+        return GraphicsContextState::combineWithAlpha(color, alpha);
+    }
+
 private:
     const GraphicsContextState* immutableState() const { return m_paintState; }
 
     GraphicsContextState* mutableState()
     {
         realizePaintSave();
         return m_paintState;
     }
 
     static void setPathFromPoints(SkPath*, size_t, const FloatPoint*);
@@ skipping 99 matching lines @@
 
     unsigned m_accelerated : 1;
     unsigned m_isCertainlyOpaque : 1;
     unsigned m_printing : 1;
     unsigned m_antialiasHairlineImages : 1;
 };
 
 } // namespace blink
 
 #endif // GraphicsContext_h