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

Source/core/html/canvas/CanvasRenderingContext2D.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008 Dirk Schulze <krit@webkit.org>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  * Copyright (C) 2012 Intel Corporation. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
@@ skipping 18 matching lines @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "config.h"
 #include "CanvasRenderingContext2D.h"
 
 #include "CSSFontSelector.h"
 #include "CSSParser.h"
 #include "CSSPropertyNames.h"
+#include "Canvas2DContextAttributes.h"
 #include "CanvasGradient.h"
 #include "CanvasPattern.h"
 #include "CanvasStyle.h"
 #include "DOMPath.h"
 #include "ExceptionCode.h"
 #include "ExceptionCodePlaceholder.h"
 #include "HTMLCanvasElement.h"
 #include "HTMLImageElement.h"
 #include "HTMLMediaElement.h"
 #include "HTMLNames.h"
@@ skipping 61 matching lines @@
         DashArray convertedLineDash(lineDash.size());
         for (size_t i = 0; i < lineDash.size(); ++i)
             convertedLineDash[i] = static_cast<DashArrayElement>(lineDash[i]);
         c->setLineDash(convertedLineDash, m_canvasContext->lineDashOffset());
     }
 
 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);
 }
 
 void CanvasRenderingContext2D::unwindStateStack()
 {
     // Ensure that the state stack in the ImageBuffer's context
     // is cleared before destruction, to avoid assertions in the
     // GraphicsContext dtor.
     if (size_t stackSize = m_stateStack.size()) {
@@ skipping 2108 matching lines @@
     if (enabled == state().m_imageSmoothingEnabled)
         return;
 
     realizeSaves();
     modifiableState().m_imageSmoothingEnabled = enabled;
     GraphicsContext* c = drawingContext();
     if (c)
         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