[HTMLCanvasElement.toBlob] Default callback version without scheduler

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 16 matching lines @@
 
 #include "config.h"
 #include "core/html/HTMLCanvasElement.h"
 
 #include "bindings/core/v8/ExceptionMessages.h"
 #include "bindings/core/v8/ExceptionState.h"
 #include "bindings/core/v8/ScriptController.h"
 #include "core/HTMLNames.h"
 #include "core/dom/Document.h"
 #include "core/dom/ExceptionCode.h"
+#include "core/fileapi/File.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
 #include "core/html/ImageData.h"
 #include "core/html/canvas/CanvasContextCreationAttributes.h"
 #include "core/html/canvas/CanvasFontCache.h"
 #include "core/html/canvas/CanvasRenderingContext.h"
 #include "core/html/canvas/CanvasRenderingContextFactory.h"
 #include "core/layout/LayoutHTMLCanvas.h"
 #include "core/paint/DeprecatedPaintLayer.h"
 #include "platform/MIMETypeRegistry.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/graphics/Canvas2DImageBufferSurface.h"
 #include "platform/graphics/ExpensiveCanvasHeuristicParameters.h"
 #include "platform/graphics/ImageBuffer.h"
 #include "platform/graphics/RecordingImageBufferSurface.h"
 #include "platform/graphics/StaticBitmapImage.h"
 #include "platform/graphics/UnacceleratedImageBufferSurface.h"
 #include "platform/graphics/gpu/AcceleratedImageBufferSurface.h"
 #include "platform/transforms/AffineTransform.h"
 #include "public/platform/Platform.h"
+#include "public/platform/WebTraceLocation.h"
+#include "wtf/Functional.h"
 #include <math.h>
 #include <v8.h>
 
 namespace blink {
 
 using namespace HTMLNames;
 
 namespace {
 
 // These values come from the WhatWG spec.
@@ skipping 464 matching lines @@
     if (!qualityArgument.isEmpty()) {
         v8::Local<v8::Value> v8Value = qualityArgument.v8Value();
         if (v8Value->IsNumber()) {
             quality = v8Value.As<v8::Number>()->Value();
             qualityPtr = &quality;
         }
     }
     return toDataURLInternal(mimeType, qualityPtr, BackBuffer);
 }
 
+void HTMLCanvasElement::toBlob(FileCallback* callback, const String& mimeType, const ScriptValue& qualityArgument, ExceptionState& exceptionState) const
+{
+    if (!originClean()) {
+        exceptionState.throwSecurityError("Tainted canvases may not be exported.");
+        return;
+    }
+
+    File* resultBlob = nullptr;
+    if (!isPaintable()) {
+        // If the canvas element's bitmap has no pixels
+        return;

[Noel Gordon, 2015/08/28 08:53:47]

I don't think the spec allows us to just return here.  What does the spec say to
do in this case?

[xlai (Olivia), 2015/08/28 19:54:19]

Acknowledged. The spec says "If the canvas element's bitmap has no pixels (i.e.
either its horizontal dimension or its vertical dimension is zero) then let
result be null.". I think I need to fix this in the next round of code review
issue by passing the null resultBlob to the call back function.

+    }
+
+    double quality;
+    if (!qualityArgument.isEmpty()) {
+        v8::Local<v8::Value> v8Value = qualityArgument.v8Value();
+        if (v8Value->IsNumber()) {
+            quality = v8Value.As<v8::Number>()->Value();
+        }
+    }
+
+    String encodingMimeType = toEncodingMimeType(mimeType);
+
+    ImageData* imageData = toImageData(BackBuffer);
+    ScopedDisposal<ImageData> disposer(imageData);
+
+    // Perform image encoding
+    Vector<char> encodedImage;
+    ImageDataBuffer(imageData->size(), imageData->data()->data()).encodeImage(encodingMimeType, &quality, &encodedImage);

[Noel Gordon, 2015/08/28 08:53:47]

encodeImage is bool returning (success/failure).  toDataURL must return "data:,"
on failure, and the <canvas> spec requires that  toBlob similarly handle the
failure case.  What does the spec say to do on failure?

Secondly, the image is encoded on the main thread here, which is not really in
the spirit of the toBlob spec (wants an aysnc encode). Is there a plan to ensure
that this image encode does not jank the main thread?  No point doing toBlob
otherwise.

[xlai (Olivia), 2015/08/28 19:54:19]

Acknowledged. I will explain in the overall message I sent to you.

+    resultBlob = File::create(encodedImage.data(), encodedImage.size(), encodingMimeType);
+
+    Platform::current()->mainThread()->postTask(FROM_HERE, bind(&FileCallback::handleEvent, callback, resultBlob));
+}
+
 SecurityOrigin* HTMLCanvasElement::securityOrigin() const
 {
     return document().securityOrigin();
 }
 
 bool HTMLCanvasElement::originClean() const
 {
     if (document().settings() && document().settings()->disableReadingFromCanvas())
         return false;
     return m_originClean;
@@ skipping 353 matching lines @@
 {
     return FloatSize(width(), height());
 }
 
 bool HTMLCanvasElement::isOpaque() const
 {
     return m_context && !m_context->hasAlpha();
 }
 
 } // blink