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

Source/bindings/v8/custom/V8HTMLCanvasElementCustom.cpp

Index: Source/bindings/v8/custom/V8HTMLCanvasElementCustom.cpp
diff --git a/Source/bindings/v8/custom/V8HTMLCanvasElementCustom.cpp b/Source/bindings/v8/custom/V8HTMLCanvasElementCustom.cpp
index dda0c9eb235930887d1d7ee858264ddbadcf3359..e19af3a7633895adbe99289dd6df8425bf125e3b 100644
--- a/Source/bindings/v8/custom/V8HTMLCanvasElementCustom.cpp
+++ b/Source/bindings/v8/custom/V8HTMLCanvasElementCustom.cpp
@@ -37,7 +37,7 @@
 #include "V8WebGLRenderingContext.h"
 #include "bindings/v8/V8Binding.h"
 #include "core/html/HTMLCanvasElement.h"
-#include "core/html/canvas/CanvasContextAttributes.h"
+#include "core/html/canvas/Canvas2DContextAttributes.h"
 #include "core/html/canvas/CanvasRenderingContext.h"
 #include "core/html/canvas/WebGLContextAttributes.h"
 #include "core/inspector/InspectorCanvasInstrumentation.h"
@@ -76,6 +76,15 @@ v8::Handle<v8::Value> V8HTMLCanvasElement::getContextMethodCustom(const v8::Argu
             if (jsAttrs->Has(preserveDrawingBuffer))
                 webGLAttrs->setPreserveDrawingBuffer(jsAttrs->Get(preserveDrawingBuffer)->BooleanValue());
         }
+    } else {
+        attrs = Canvas2DContextAttributes::create();
+        Canvas2DContextAttributes* canvas2DAttrs = static_cast<Canvas2DContextAttributes*>(attrs.get());

[jamesr, 2013/04/26 00:41:31]

do you have to downcast? can you just keep a more specific pointer and then
assign it to the base attrs after the fact?

[Stephen White, 2013/04/26 15:51:03]

Good point. I was blindly following the pattern of the WebGL case above. I've
changed them both.

+        if (args.Length() > 1 && args[1]->IsObject()) {
+            v8::Handle<v8::Object> jsAttrs = args[1]->ToObject();
+            v8::Handle<v8::String> alpha = v8::String::NewSymbol("alpha");
+            if (jsAttrs->Has(alpha))
+                canvas2DAttrs->setAlpha(jsAttrs->Get(alpha)->BooleanValue());

[jamesr, 2013/04/26 00:41:31]

this seems to imply that the default value for 'alpha' is false, but don't 2d
canvases get an alpha channel by default?

[Stephen White, 2013/04/26 15:51:03]

I think this should work: Canvas2DContextAttributes::m_alpha is set to true in
the constructor, so if the object isn't specified, or if it doesn't contain an
"alpha" property, it should default to true.  I've added a test case for the
latter (the former is test case 1).

+        }
     }
     CanvasRenderingContext* result = imp->getContext(contextId, attrs.get());
     if (!result)