Make SVG painting independent of GraphicsContext's alpha state

Source/platform/graphics/GraphicsContextState.cpp

 // Copyright (c) 2014 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.
 
 #include "config.h"
 #include "platform/graphics/GraphicsContextState.h"
 
 #include "platform/graphics/skia/SkiaUtils.h"
 
 namespace blink {
@@ skipping 81 matching lines @@
 
 void GraphicsContextState::setStrokeColor(const Color& color)
 {
     m_strokeGradient.clear();
     m_strokePattern.clear();
     m_strokeColor = color;
     m_strokePaint.setColor(applyAlpha(color.rgb()));
     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());
 }
 
 void GraphicsContextState::clearStrokeGradient()
 {
     m_strokeGradient.clear();
     ASSERT(!m_strokePattern);
     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());
 }
 
 void GraphicsContextState::clearStrokePattern()
 {
     m_strokePattern.clear();
     ASSERT(!m_strokeGradient);
     m_strokePaint.setColor(applyAlpha(m_strokeColor.rgb()));
 }
 
@@ skipping 17 matching lines @@
 
 void GraphicsContextState::setFillColor(const Color& color)
 {
     m_fillColor = color;
     m_fillGradient.clear();
     m_fillPattern.clear();
     m_fillPaint.setColor(applyAlpha(color.rgb()));
     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());
 }
 
 void GraphicsContextState::clearFillGradient()
 {
     m_fillGradient.clear();
     ASSERT(!m_fillPattern);
     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());
 }
 
 void GraphicsContextState::clearFillPattern()
 {
     m_fillPattern.clear();
     ASSERT(!m_fillGradient);
     m_fillPaint.setColor(applyAlpha(m_fillColor.rgb()));
 }
 
@@ skipping 17 matching lines @@
     m_dropShadowImageFilter = dropShadowImageFilter;
 }
 
 void GraphicsContextState::clearDropShadowImageFilter()
 {
     m_dropShadowImageFilter.clear();
 }
 
 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()));
 }
 
 void GraphicsContextState::setLineDash(const DashArray& dashes, float dashOffset)
 {
     m_strokeData.setLineDash(dashes, dashOffset);
 }
 
 void GraphicsContextState::setColorFilter(PassRefPtr<SkColorFilter> colorFilter)
@@ skipping 29 matching lines @@
     return m_hasComplexClip;
 }
 
 void GraphicsContextState::setHasComplexClip()
 {
     m_hasComplexClip = true;
 }
 
 
 } // namespace blink