Implement Asynchronous image encoding for Canvas.toBlob

third_party/WebKit/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 28 matching lines @@
 #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/Task.h"
+#include "platform/ThreadSafeFunctional.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.
 const int DefaultWidth = 300;
 const int DefaultHeight = 150;
 
 // Firefox limits width/height to 32767 pixels, but slows down dramatically before it
 // reaches that limit. We limit by area instead, giving us larger maximum dimensions,
 // in exchange for a smaller maximum canvas size.
 const int MaxCanvasArea = 32768 * 8192; // Maximum canvas area in CSS pixels
 
 // In Skia, we will also limit width/height to 32767.
 const int MaxSkiaDim = 32767; // Maximum width/height in CSS pixels.
 
+// A default value of quality argument for toDataURL and toBlob
+// It is in an invalid range (outside 0.0 - 1.0) so that it will not be misinterpreted as a user-input value
+const int UndefinedQualityValue = -1.0;
+
 bool canCreateImageBuffer(const IntSize& size)
 {
     if (size.isEmpty())
         return false;
     if (size.width() * size.height() > MaxCanvasArea)
         return false;
     if (size.width() > MaxSkiaDim || size.height() > MaxSkiaDim)
         return false;
     return true;
 }
@@ skipping 30 matching lines @@
 {
     v8::Isolate::GetCurrent()->AdjustAmountOfExternalAllocatedMemory(-m_externallyAllocatedMemory);
 #if !ENABLE(OILPAN)
     for (CanvasObserver* canvasObserver : m_observers)
         canvasObserver->canvasDestroyed(this);
     // Ensure these go away before the ImageBuffer.
     m_context.clear();
 #endif
 }
 
+OwnPtr<WebThread>& HTMLCanvasElement::getToBlobThreadInstance()
+{
+    DEFINE_STATIC_LOCAL(OwnPtr<WebThread>, s_toBlobThread, ());
+    if (!s_toBlobThread) {
+        s_toBlobThread = adoptPtr(Platform::current()->createThread("Async toBlob"));
+    }
+    return s_toBlobThread;

[Justin Novosad, 2015/09/25 16:47:33]

Returning an "OwnPtr<WebThread>&" is not appropriate. The return type should be
WebThread* and it should return s_toBlobThread.get(). Otherwise, this looks good
to me.

+}
+
 void HTMLCanvasElement::parseAttribute(const QualifiedName& name, const AtomicString& value)
 {
     if (name == widthAttr || name == heightAttr)
         reset();
     HTMLElement::parseAttribute(name, value);
 }
 
 LayoutObject* HTMLCanvasElement::createLayoutObject(const ComputedStyle& style)
 {
     LocalFrame* frame = document().frame();
@@ skipping 369 matching lines @@
     ASSERT(m_context->is2d());
     RefPtr<SkImage> snapshot = buffer()->newSkImageSnapshot(PreferNoAcceleration);
     if (snapshot) {
         SkImageInfo imageInfo = SkImageInfo::Make(width(), height(), kRGBA_8888_SkColorType, kUnpremul_SkAlphaType);
         snapshot->readPixels(imageInfo, imageData->data()->data(), imageInfo.minRowBytes(), 0, 0);
     }
 
     return imageData;
 }
 
-String HTMLCanvasElement::toDataURLInternal(const String& mimeType, const double* quality, SourceDrawingBuffer sourceBuffer) const
+String HTMLCanvasElement::toDataURLInternal(const String& mimeType, const double& quality, SourceDrawingBuffer sourceBuffer) const
 {
     if (!isPaintable())
         return String("data:,");
 
     String encodingMimeType = toEncodingMimeType(mimeType);
 
     ImageData* imageData = toImageData(sourceBuffer);
     ScopedDisposal<ImageData> disposer(imageData);
 
     return ImageDataBuffer(imageData->size(), imageData->data()->data()).toDataURL(encodingMimeType, quality);
 }
 
 String HTMLCanvasElement::toDataURL(const String& mimeType, const ScriptValue& qualityArgument, ExceptionState& exceptionState) const
 {
     if (!originClean()) {
         exceptionState.throwSecurityError("Tainted canvases may not be exported.");
         return String();
     }
-    double quality;
-    double* qualityPtr = nullptr;
+    double quality = UndefinedQualityValue;
     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);
+    return toDataURLInternal(mimeType, quality, BackBuffer);
 }
 
-void HTMLCanvasElement::toBlob(FileCallback* callback, const String& mimeType, const ScriptValue& qualityArgument, ExceptionState& exceptionState) const
+void HTMLCanvasElement::encodeImageAsync(DOMUint8ClampedArray* imageData, IntSize imageSize, FileCallback* callback, const String& mimeType, double quality)
+{
+    OwnPtr<Vector<char>> encodedImage(adoptPtr(new Vector<char>()));
+
+    if (!ImageDataBuffer(imageSize, imageData->data()).encodeImage(mimeType, quality, encodedImage.get())) {
+        Platform::current()->mainThread()->taskRunner()->postTask(FROM_HERE, bind(&FileCallback::handleEvent, callback, nullptr));
+    } else {
+        Platform::current()->mainThread()->taskRunner()->postTask(FROM_HERE, threadSafeBind(&HTMLCanvasElement::createBlobAndCall, AllowCrossThreadAccess(this), encodedImage.release(), mimeType, AllowCrossThreadAccess(callback)));
+    }
+}
+
+void HTMLCanvasElement::createBlobAndCall(PassOwnPtr<Vector<char>> encodedImage, const String& mimeType, FileCallback* callback)
+{
+    // The main thread takes ownership of encoded image vector
+    OwnPtr<Vector<char>> enc(encodedImage);
+
+    File* resultBlob = File::create(enc->data(), enc->size(), mimeType);
+    Platform::current()->mainThread()->taskRunner()->postTask(FROM_HERE, bind(&FileCallback::handleEvent, callback, resultBlob));
+}
+
+void HTMLCanvasElement::toBlob(FileCallback* callback, const String& mimeType, const ScriptValue& qualityArgument, ExceptionState& exceptionState)
 {
     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
+        Platform::current()->mainThread()->taskRunner()->postTask(FROM_HERE, bind(&FileCallback::handleEvent, callback, nullptr));
         return;
     }
 
-    double quality;
-    double* qualityPtr = nullptr;
+    double quality = UndefinedQualityValue;
     if (!qualityArgument.isEmpty()) {
         v8::Local<v8::Value> v8Value = qualityArgument.v8Value();
         if (v8Value->IsNumber()) {
             quality = v8Value.As<v8::Number>()->Value();
-            qualityPtr = &quality;
         }
     }
 
     String encodingMimeType = toEncodingMimeType(mimeType);
 
     ImageData* imageData = toImageData(BackBuffer);
+    // imageData unref its data, which we still keep alive for the async toBlob thread
     ScopedDisposal<ImageData> disposer(imageData);
 
-    // Perform image encoding
-    Vector<char> encodedImage;
-    ImageDataBuffer(imageData->size(), imageData->data()->data()).encodeImage(encodingMimeType, qualityPtr, &encodedImage);
-    resultBlob = File::create(encodedImage.data(), encodedImage.size(), encodingMimeType);
+    // Add a ref to keep image data alive until completion of encoding
+    RefPtr<DOMUint8ClampedArray> imageDataRef(imageData->data());
 
-    Platform::current()->mainThread()->taskRunner()->postTask(FROM_HERE, bind(&FileCallback::handleEvent, callback, resultBlob));
+    // TODO: We cannot guarantee that 'this' will stay alive long enough. 
+    getToBlobThreadInstance()->taskRunner()->postTask(FROM_HERE, new Task(threadSafeBind(&HTMLCanvasElement::encodeImageAsync, AllowCrossThreadAccess(this), AllowCrossThreadAccess(imageDataRef.release().leakRef()), imageData->size(), AllowCrossThreadAccess(callback), encodingMimeType, quality)));
 }
 
 SecurityOrigin* HTMLCanvasElement::securityOrigin() const
 {
     return document().securityOrigin();
 }
 
 bool HTMLCanvasElement::originClean() const
 {
     if (document().settings() && document().settings()->disableReadingFromCanvas())
@@ skipping 355 matching lines @@
 {
     return FloatSize(width(), height());
 }
 
 bool HTMLCanvasElement::isOpaque() const
 {
     return m_context && !m_context->hasAlpha();
 }
 
 } // blink