Implement image-rendering:pixelated for accelerated 2D canvases.

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 135 matching lines @@
     return HTMLElement::createRenderer(style);
 }
 
 void HTMLCanvasElement::didRecalcStyle(StyleRecalcChange)
 {
     SkPaint::FilterLevel filterLevel = computedStyle()->imageRendering() == ImageRenderingPixelated ? SkPaint::kNone_FilterLevel : SkPaint::kLow_FilterLevel;
     if (m_context && m_context->is3d()) {
         toWebGLRenderingContext(m_context.get())->setFilterLevel(filterLevel);
         setNeedsCompositingUpdate();
     }
+    if (hasImageBuffer())
+        m_imageBuffer->setFilterLevel(filterLevel);
 }
 
 Node::InsertionNotificationRequest HTMLCanvasElement::insertedInto(ContainerNode* node)
 {
     setIsInCanvasSubtree(true);
     return HTMLElement::insertedInto(node);
 }
 
 void HTMLCanvasElement::addObserver(CanvasObserver* observer)
 {
@@ skipping 451 matching lines @@
     m_imageBufferIsClear = true;
 
     if (!canCreateImageBuffer(size()))
         return;
 
     int msaaSampleCount;
     OwnPtr<ImageBufferSurface> surface = createImageBufferSurface(size(), &msaaSampleCount);
     if (!surface->isValid())
         return;
 
+    document().updateRenderTreeIfNeeded();
+    RenderStyle* style = computedStyle();
+    bool pixelated = style && (style->imageRendering() == ImageRenderingPixelated || style->imageRendering() == ImageRenderingOptimizeContrast);
+
     m_imageBuffer = ImageBuffer::create(surface.release());
     m_imageBuffer->setClient(this);
+    m_imageBuffer->setFilterLevel(pixelated ? SkPaint::kNone_FilterLevel : SkPaint::kLow_FilterLevel);

[esprehn, 2014/12/16 19:22:32]

You don't need this line or the bool pixelated or the computedStyle() call. Just
invoke updateRenderTreeIfNeeded on this line after seting m_imageBuffer and the
willRecalcStyle callback will do this work.

[jackhou1, 2014/12/17 01:28:09]

This is what I tried earlier but it didn't work. I may have done something
wrong. I've uploaded it as Patch Set 25 if you want to take a look. My
understanding is that the style may already be calculated before
createImageBufferInternal is called, but setFilterLevel is not called because
there was no image buffer at the time; when the image buffer is created,
updateRenderTreeIfNeeded doesn't recalc the style because it thinks it's already
done. 

 
     m_didFailToCreateImageBuffer = false;
 
     updateExternallyAllocatedMemory();
 
     if (is3D()) {
         // Early out for WebGL canvases
         return;
     }
 
     m_imageBuffer->setClient(this);
     m_imageBuffer->context()->setShouldClampToSourceRect(false);
     m_imageBuffer->context()->disableAntialiasingOptimizationForHairlineImages();
-    m_imageBuffer->context()->setImageInterpolationQuality(CanvasDefaultInterpolationQuality);
+    m_imageBuffer->context()->setImageInterpolationQuality(pixelated ? InterpolationLow : CanvasDefaultInterpolationQuality);

[esprehn, 2014/12/16 19:22:32]

Doesn't this need to be dynamically updated in willRecalcStyle?

[jackhou1, 2014/12/17 01:28:09]

Done.

     // Enabling MSAA overrides a request to disable antialiasing. This is true regardless of whether the
     // rendering mode is accelerated or not. For consistency, we don't want to apply AA in accelerated
     // canvases but not in unaccelerated canvases.
     if (!msaaSampleCount && document().settings() && !document().settings()->antialiased2dCanvasEnabled())
         m_imageBuffer->context()->setShouldAntialias(false);
     // GraphicsContext's defaults don't always agree with the 2d canvas spec.
     // See CanvasRenderingContext2D::State::State() for more information.
     m_imageBuffer->context()->setMiterLimit(10);
     m_imageBuffer->context()->setStrokeThickness(1);
 #if ENABLE(ASSERT)
@@ skipping 150 matching lines @@
     if (!isPaintable()) {
         *status = InvalidSourceImageStatus;
         return nullptr;
     }
 
     if (!m_context) {
         *status = NormalSourceImageStatus;
         return createTransparentImage(size());
     }
 
+    m_imageBuffer->willAccessPixels();
+
     if (m_context->is3d()) {
         m_context->paintRenderingResultsToCanvas(BackBuffer);
         *status = ExternalSourceImageStatus;
 
         // can't create SkImage from WebGLImageBufferSurface (contains only SkBitmap)
         return buffer()->copyImage(DontCopyBackingStore, Unscaled);
     }
 
     RefPtr<SkImage> image = buffer()->newImageSnapshot();
     if (image) {
         *status = NormalSourceImageStatus;
         return StaticBitmapImage::create(image.release());
     }
 
     *status = InvalidSourceImageStatus;
     return nullptr;
 }
 
 bool HTMLCanvasElement::wouldTaintOrigin(SecurityOrigin*) const
 {
     return !originClean();
 }
 
 FloatSize HTMLCanvasElement::sourceSize() const
 {
     return FloatSize(width(), height());
 }
 
 }