Add image-rendering: pixelated.

Source/core/rendering/RenderHTMLCanvas.cpp

 /*
  * Copyright (C) 2004, 2006, 2007 Apple Inc. 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.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 49 matching lines @@
 
     bool clip = !contentRect.contains(paintRect);
     if (clip) {
         // Not allowed to overflow the content box.
         paintInfo.context->save();
         paintInfo.context->clip(pixelSnappedIntRect(contentRect));
     }
 
     // FIXME: InterpolationNone should be used if ImageRenderingOptimizeContrast is set.
     // See bug for more details: crbug.com/353716.
-    InterpolationQuality interpolationQuality = style()->imageRendering() == ImageRenderingOptimizeContrast ? InterpolationLow : CanvasDefaultInterpolationQuality;
+    InterpolationQuality interpolationQuality;
+    switch (style()->imageRendering()) {
+    case ImageRenderingOptimizeContrast:
+        interpolationQuality = InterpolationLow;

[Mike Lawther (Google), 2014/06/20 04:26:50]

These should really be the same, ie InterpolationNone. From memory, it was only
set to InterpolationLow because that was the value that CoreGraphics used to
mean 'nearest neighbour'

[jackhou, 2014/06/20 07:14:44]

Done.

[jackhou, 2014/06/20 08:35:42]

I realized this would require updating all the tests, which differ by platform.
Also, it would be shipped immediately, whereas pixelated is still experimental.
So probably best to leave it unchanged for now and address it in the follow-up
CL.

+        break;
+    case ImageRenderingPixelated:
+        interpolationQuality = InterpolationNone;

[Mike Lawther (Google), 2014/06/20 04:26:50]

Strictly according to spec, we only use nearest neighbour if we are scaling up.
If we are scaling down, then we should be using the default scaling (quoth the
spec: "When scaling the image up, the "nearest neighbor" or similar algorithm
must be used, so that the image appears to be simply composed of very large
pixels. When scaling down, this is the same as auto.").

I'm fine with filing a bug about this with a FIXME.

[jackhou, 2014/06/20 07:14:44]

Done.

+        break;
+    default:
+        interpolationQuality = CanvasDefaultInterpolationQuality;
+    }
+
     InterpolationQuality previousInterpolationQuality = context->imageInterpolationQuality();
     context->setImageInterpolationQuality(interpolationQuality);
     toHTMLCanvasElement(node())->paint(context, paintRect);
     context->setImageInterpolationQuality(previousInterpolationQuality);
 
     if (clip)
         context->restore();
 }
 
 void RenderHTMLCanvas::canvasSizeChanged()
@@ skipping 28 matching lines @@
         return CompositingReasonNone;
 
     HTMLCanvasElement* canvas = toHTMLCanvasElement(node());
     if (canvas->renderingContext() && canvas->renderingContext()->isAccelerated())
         return CompositingReasonCanvas;
 
     return CompositingReasonNone;
 }
 
 } // namespace WebCore