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

Source/core/html/HTMLCanvasElement.cpp

 /*
  * Copyright (C) 2004, 2006, 2007 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 13 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 "HTMLCanvasElement.h"
 
 #include <math.h>
 #include <stdio.h>
 #include "Attribute.h"
-#include "CanvasContextAttributes.h"
+#include "Canvas2DContextAttributes.h"
 #include "CanvasGradient.h"
 #include "CanvasPattern.h"
 #include "CanvasRenderingContext2D.h"
 #include "CanvasStyle.h"
 #include "Document.h"
 #include "ExceptionCode.h"
 #include "HTMLNames.h"
 #include "ImageData.h"
 #include "ScriptController.h"
 #include "WebCoreMemoryInstrumentation.h"
 #include "core/page/Chrome.h"
 #include "core/page/Frame.h"
 #include "core/page/Page.h"
+#include "core/page/RuntimeEnabledFeatures.h"
 #include "core/page/Settings.h"
 #include "core/platform/MIMETypeRegistry.h"
 #include "core/platform/graphics/GraphicsContext.h"
 #include "core/platform/graphics/ImageBuffer.h"
 #include "core/rendering/RenderHTMLCanvas.h"
 
 #include "WebGLContextAttributes.h"
 #include "WebGLRenderingContext.h"
 
 #include <public/Platform.h>
@@ skipping 95 matching lines @@
 CanvasRenderingContext* HTMLCanvasElement::getContext(const String& type, CanvasContextAttributes* attrs)
 {
     // A Canvas can either be "2D" or "webgl" but never both. If you request a 2D canvas and the existing
     // context is already 2D, just return that. If the existing context is WebGL, then destroy it
     // before creating a new 2D context. Vice versa when requesting a WebGL canvas. Requesting a
     // context with any other type string will destroy any existing context.
     
     // FIXME - The code depends on the context not going away once created, to prevent JS from
     // seeing a dangling pointer. So for now we will disallow the context from being changed
     // once it is created.
+    Settings* settings = document()->settings();

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

not sure why this moved, it doesn't appear to be used

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

Leftover from an earlier change.  Reverted.

     if (type == "2d") {
         if (m_context && !m_context->is2d())
             return 0;
         if (!m_context) {
-            m_context = CanvasRenderingContext2D::create(this, document()->inQuirksMode());
+            m_context = CanvasRenderingContext2D::create(this, RuntimeEnabledFeatures::experimentalCanvasFeaturesEnabled() ? static_cast<Canvas2DContextAttributes*>(attrs) : 0, document()->inQuirksMode());
             if (m_context) {
                 // Need to make sure a RenderLayer and compositing layer get created for the Canvas
                 setNeedsStyleRecalc(SyntheticStyleChange);
             }
         }
         return m_context.get();
     }
 
-    Settings* settings = document()->settings();
     if (settings && settings->webGLEnabled()) {
 
         // Accept the legacy "webkit-3d" name as well as the provisional "experimental-webgl" name.
         bool is3dContext = (type == "webkit-3d") || (type == "experimental-webgl");
 
 #if !OS(ANDROID)
         // Now that WebGL is ratified, we will also accept "webgl" as the context name in Chrome.
         is3dContext |= (type == "webgl");
 #endif
 
@@ skipping 139 matching lines @@
     if (m_context) {
         if (!paintsIntoCanvasBuffer() && !document()->printing())
             return;
         m_context->paintRenderingResultsToCanvas();
     }
 
     if (hasCreatedImageBuffer()) {
         ImageBuffer* imageBuffer = buffer();
         if (imageBuffer) {
             if (m_presentedImage)
-                context->drawImage(m_presentedImage.get(), ColorSpaceDeviceRGB, pixelSnappedIntRect(r), CompositeSourceOver, DoNotRespectImageOrientation, useLowQualityScale);
+                context->drawImage(m_presentedImage.get(), ColorSpaceDeviceRGB, pixelSnappedIntRect(r), !m_context || m_context->hasAlpha() ? CompositeSourceOver : CompositeCopy, DoNotRespectImageOrientation, useLowQualityScale);

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

i'd suggest moving the ternary bit out to a local since it's duplicated in both
the if and else branches

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

Done.

             else
-                context->drawImageBuffer(imageBuffer, ColorSpaceDeviceRGB, pixelSnappedIntRect(r), CompositeSourceOver, BlendModeNormal, useLowQualityScale);
+                context->drawImageBuffer(imageBuffer, ColorSpaceDeviceRGB, pixelSnappedIntRect(r), !m_context || m_context->hasAlpha() ? CompositeSourceOver : CompositeCopy, BlendModeNormal, useLowQualityScale);
         }
     }
 
     if (is3D())
         static_cast<WebGLRenderingContext*>(m_context.get())->markLayerComposited();
 }
 
 bool HTMLCanvasElement::is3D() const
 {
     return m_context && m_context->is3d();
@@ skipping 147 matching lines @@
         return;
 
     if (deviceSize.width() > MaxSkiaDim || deviceSize.height() > MaxSkiaDim)
         return;
 
     IntSize bufferSize(deviceSize.width(), deviceSize.height());
     if (!bufferSize.width() || !bufferSize.height())
         return;
 
     RenderingMode renderingMode = shouldAccelerate(bufferSize) ? Accelerated : UnacceleratedNonPlatformBuffer;
-
-    m_imageBuffer = ImageBuffer::create(size(), m_deviceScaleFactor, ColorSpaceDeviceRGB, renderingMode);
+    OpacityMode opacityMode = !m_context || m_context->hasAlpha() ? NonOpaque : Opaque;
+    m_imageBuffer = ImageBuffer::create(size(), m_deviceScaleFactor, ColorSpaceDeviceRGB, renderingMode, opacityMode);
     if (!m_imageBuffer)
         return;
     m_imageBuffer->context()->setShadowsIgnoreTransforms(true);
     m_imageBuffer->context()->setImageInterpolationQuality(DefaultInterpolationQuality);
     if (document()->settings() && !document()->settings()->antialiased2dCanvasEnabled())
         m_imageBuffer->context()->setShouldAntialias(false);
     m_imageBuffer->context()->setStrokeThickness(1);
     m_contextStateSaver = adoptPtr(new GraphicsContextStateSaver(*m_imageBuffer->context()));
 
     if (m_context && m_context->is2d()) {
@@ skipping 71 matching lines @@
     HTMLElement::reportMemoryUsage(memoryObjectInfo);
     info.addMember(m_observers, "observers");
     info.addMember(m_context, "context");
     info.addMember(m_imageBuffer, "imageBuffer");
     info.addMember(m_contextStateSaver, "contextStateSaver");
     info.addMember(m_presentedImage, "presentedImage");
     info.addMember(m_copiedImage, "copiedImage");
 }
 
 }