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

Source/bindings/v8/custom/V8HTMLCanvasElementCustom.cpp

 /*
  * Copyright (C) 2007-2009 Google Inc. All rights reserved.
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 19 matching lines @@
  */
 
 #include "config.h"
 #include "V8HTMLCanvasElement.h"
 
 #include "V8CanvasRenderingContext2D.h"
 #include "V8Node.h"
 #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"
 #include "wtf/MathExtras.h"
 #include "wtf/text/WTFString.h"
 
 namespace WebCore {
 
 v8::Handle<v8::Value> V8HTMLCanvasElement::getContextMethodCustom(const v8::Arguments& args)
 {
@@ skipping 18 matching lines @@
             v8::Handle<v8::String> antialias = v8::String::NewSymbol("antialias");
             if (jsAttrs->Has(antialias))
                 webGLAttrs->setAntialias(jsAttrs->Get(antialias)->BooleanValue());
             v8::Handle<v8::String> premultipliedAlpha = v8::String::NewSymbol("premultipliedAlpha");
             if (jsAttrs->Has(premultipliedAlpha))
                 webGLAttrs->setPremultipliedAlpha(jsAttrs->Get(premultipliedAlpha)->BooleanValue());
             v8::Handle<v8::String> preserveDrawingBuffer = v8::String::NewSymbol("preserveDrawingBuffer");
             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)
         return v8Null(args.GetIsolate());
     else if (result->is2d()) {
         v8::Handle<v8::Value> v8Result = toV8Fast(static_cast<CanvasRenderingContext2D*>(result), args, imp);
         if (InspectorInstrumentation::canvasAgentEnabled(imp->document())) {
             ScriptState* scriptState = ScriptState::forContext(v8::Context::GetCurrent());
             ScriptObject context(scriptState, v8::Handle<v8::Object>::Cast(v8Result));
             ScriptObject wrapped = InspectorInstrumentation::wrapCanvas2DRenderingContextForInstrumentation(imp->document(), context);
@@ skipping 30 matching lines @@
         quality = args[1]->NumberValue();
         qualityPtr = &quality;
     }
 
     String result = canvas->toDataURL(type, qualityPtr, ec);
     setDOMException(ec, args.GetIsolate());
     return v8StringOrUndefined(result, args.GetIsolate());
 }
 
 } // namespace WebCore