This CL implements the first draft of Canvas 2D Context Attributes, aka getContext('2d', { alpha: f…

Source/core/html/canvas/CanvasRenderingContext2D.cpp

Index: Source/core/html/canvas/CanvasRenderingContext2D.cpp
diff --git a/Source/core/html/canvas/CanvasRenderingContext2D.cpp b/Source/core/html/canvas/CanvasRenderingContext2D.cpp
index b5476f00e5af475c8425e7e033fdca5f6a88b8b1..18662e7fb791d45cb8871366ecec9f292e6cfae6 100644
--- a/Source/core/html/canvas/CanvasRenderingContext2D.cpp
+++ b/Source/core/html/canvas/CanvasRenderingContext2D.cpp
@@ -36,6 +36,7 @@
 #include "CSSFontSelector.h"
 #include "CSSParser.h"
 #include "CSSPropertyNames.h"
+#include "Canvas2DContextAttributes.h"
 #include "CanvasGradient.h"
 #include "CanvasPattern.h"
 #include "CanvasStyle.h"
@@ -117,11 +118,12 @@ private:
     CanvasRenderingContext2D* m_canvasContext;
 };
 
-CanvasRenderingContext2D::CanvasRenderingContext2D(HTMLCanvasElement* canvas, bool usesCSSCompatibilityParseMode)
+CanvasRenderingContext2D::CanvasRenderingContext2D(HTMLCanvasElement* canvas, const Canvas2DContextAttributes* attrs, bool usesCSSCompatibilityParseMode)
     : CanvasRenderingContext(canvas)
     , m_stateStack(1)
     , m_unrealizedSaveCount(0)
     , m_usesCSSCompatibilityParseMode(usesCSSCompatibilityParseMode)
+    , m_hasAlpha(!attrs || attrs->alpha())
 {
     ScriptWrappable::init(this);
 }
@@ -2250,4 +2252,13 @@ void CanvasRenderingContext2D::setWebkitImageSmoothingEnabled(bool enabled)
         c->setImageInterpolationQuality(enabled ? DefaultInterpolationQuality : InterpolationNone);
 }
 
+PassRefPtr<Canvas2DContextAttributes> CanvasRenderingContext2D::getContextAttributes() const
+{
+    // We always need to return a new Canvas2DContextAttributes object to
+    // prevent the user from mutating any cached version.

[jamesr, 2013/04/26 18:30:09]

i don't follow - what is the 'user' here? javascript?

[Stephen White, 2013/04/26 18:53:18]

This comment was lifted from WebGLRenderingContext::getContextAttributes().

s/user/caller/

+    RefPtr<Canvas2DContextAttributes> attributes = Canvas2DContextAttributes::create();
+    attributes->setAlpha(m_hasAlpha);
+    return attributes.release();
+}
+
 } // namespace WebCore