Make SVG painting independent of GraphicsContext's alpha state

Source/platform/graphics/GraphicsContextState.cpp

Index: Source/platform/graphics/GraphicsContextState.cpp
diff --git a/Source/platform/graphics/GraphicsContextState.cpp b/Source/platform/graphics/GraphicsContextState.cpp
index a87bafe2a852ecdb0f916795e79e5982ed1f8cec..39fbf89eb777a7d04d525a3e7f735a17696ebbe2 100644
--- a/Source/platform/graphics/GraphicsContextState.cpp
+++ b/Source/platform/graphics/GraphicsContextState.cpp
@@ -99,12 +99,12 @@ void GraphicsContextState::setStrokeColor(const Color& color)
     m_strokePaint.setShader(0);
 }
 
-void GraphicsContextState::setStrokeGradient(const PassRefPtr<Gradient> gradient)
+void GraphicsContextState::setStrokeGradient(const PassRefPtr<Gradient> gradient, float additionalAlpha)
 {
     m_strokeColor = Color::black;
     m_strokePattern.clear();
     m_strokeGradient = gradient;
-    m_strokePaint.setColor(applyAlpha(SK_ColorBLACK));
+    m_strokePaint.setColor(combineWithAlpha(applyAlpha(SK_ColorBLACK), additionalAlpha));
     m_strokePaint.setShader(m_strokeGradient->shader());
 }
 
@@ -115,12 +115,12 @@ void GraphicsContextState::clearStrokeGradient()
     m_strokePaint.setColor(applyAlpha(m_strokeColor.rgb()));
 }
 
-void GraphicsContextState::setStrokePattern(const PassRefPtr<Pattern> pattern)
+void GraphicsContextState::setStrokePattern(const PassRefPtr<Pattern> pattern, float additionalAlpha)
 {
     m_strokeColor = Color::black;
     m_strokeGradient.clear();
     m_strokePattern = pattern;
-    m_strokePaint.setColor(applyAlpha(SK_ColorBLACK));
+    m_strokePaint.setColor(combineWithAlpha(applyAlpha(SK_ColorBLACK), additionalAlpha));
     m_strokePaint.setShader(m_strokePattern->shader());
 }
 
@@ -158,12 +158,12 @@ void GraphicsContextState::setFillColor(const Color& color)
     m_fillPaint.setShader(0);
 }
 
-void GraphicsContextState::setFillGradient(const PassRefPtr<Gradient> gradient)
+void GraphicsContextState::setFillGradient(const PassRefPtr<Gradient> gradient, float additionalAlpha)
 {
     m_fillColor = Color::black;
     m_fillPattern.clear();
     m_fillGradient = gradient;
-    m_fillPaint.setColor(applyAlpha(SK_ColorBLACK));
+    m_fillPaint.setColor(combineWithAlpha(applyAlpha(SK_ColorBLACK), additionalAlpha));
     m_fillPaint.setShader(m_fillGradient->shader());
 }
 
@@ -174,12 +174,12 @@ void GraphicsContextState::clearFillGradient()
     m_fillPaint.setColor(applyAlpha(m_fillColor.rgb()));
 }
 
-void GraphicsContextState::setFillPattern(const PassRefPtr<Pattern> pattern)
+void GraphicsContextState::setFillPattern(const PassRefPtr<Pattern> pattern, float additionalAlpha)
 {
     m_fillColor = Color::black;
     m_fillGradient.clear();
     m_fillPattern = pattern;
-    m_fillPaint.setColor(applyAlpha(SK_ColorBLACK));
+    m_fillPaint.setColor(combineWithAlpha(applyAlpha(SK_ColorBLACK), additionalAlpha));
     m_fillPaint.setShader(m_fillPattern->shader());
 }
 
@@ -217,13 +217,7 @@ void GraphicsContextState::clearDropShadowImageFilter()
 
 void GraphicsContextState::setAlphaAsFloat(float alpha)
 {
-    if (alpha < 0) {
-        m_alpha = 0;
-    } else {
-        m_alpha = roundf(alpha * 256);
-        if (m_alpha > 256)
-            m_alpha = 256;
-    }
+    m_alpha = clampedAlphaForBlending(alpha);

[chrishtr, 2015/02/02 23:14:54]

This is the one place that reads m_alpha it seems:

https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

Painting video into a transparency canvas? What is this?

[pdr., 2015/02/03 00:09:48]

GraphicsContext::preparePaintForDrawRectToRect is probably the most important
user. I think this is primarily for canvas where you can control the global
alpha state. Instead of passing the alpha through all of the drawImage calls, we
just set it on the canvas and then read it before drawing images/videos.

     m_strokePaint.setColor(applyAlpha(m_strokeColor.rgb()));
     m_fillPaint.setColor(applyAlpha(m_fillColor.rgb()));
 }