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

Source/core/html/HTMLCanvasElement.cpp

Index: Source/core/html/HTMLCanvasElement.cpp
diff --git a/Source/core/html/HTMLCanvasElement.cpp b/Source/core/html/HTMLCanvasElement.cpp
index 0bbefb7132038931f62c17e0fbc5c1dc773dc6cf..f8fa78de4095cdd2e013d71345da109b8541f8e8 100644
--- a/Source/core/html/HTMLCanvasElement.cpp
+++ b/Source/core/html/HTMLCanvasElement.cpp
@@ -31,7 +31,7 @@
 #include <math.h>
 #include <stdio.h>
 #include "Attribute.h"
-#include "CanvasContextAttributes.h"
+#include "Canvas2DContextAttributes.h"
 #include "CanvasGradient.h"
 #include "CanvasPattern.h"
 #include "CanvasRenderingContext2D.h"
@@ -45,6 +45,7 @@
 #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"
@@ -160,11 +161,12 @@ CanvasRenderingContext* HTMLCanvasElement::getContext(const String& type, Canvas
     // 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();
     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);
@@ -173,7 +175,6 @@ CanvasRenderingContext* HTMLCanvasElement::getContext(const String& type, Canvas
         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.
@@ -333,9 +334,9 @@ void HTMLCanvasElement::paint(GraphicsContext* context, const LayoutRect& r, boo
         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);
             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);
         }
     }
 
@@ -503,8 +504,8 @@ void HTMLCanvasElement::createImageBuffer() const
         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);