Don't turn off anti-aliasing for image backgrounds unless the device scale factor is large enough.

Source/core/paint/ImagePainter.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/paint/ImagePainter.h"
 
 #include "core/dom/Document.h"
 #include "core/dom/Element.h"
 #include "core/editing/FrameSelection.h"
@@ skipping 182 matching lines @@
     InspectorInstrumentation::willPaintImage(&m_renderImage);
 
     InterpolationQuality previousInterpolationQuality = context->imageInterpolationQuality();
     context->setImageInterpolationQuality(interpolationQuality);
     context->drawImage(image.get(), alignedRect, CompositeSourceOver, m_renderImage.shouldRespectImageOrientation());
     context->setImageInterpolationQuality(previousInterpolationQuality);
 
     InspectorInstrumentation::didPaintImage(&m_renderImage);
 }
 
+float deviceScaleFactor(LocalFrame*);

[jbroman, 2014/11/14 19:13:47]

drive-by: Why not include Page.h? Declaring extern functions within source files
seems odd.

[enne (OOO), 2014/11/14 19:15:59]

What is this, an extern? Maybe you should just add the right include?

[chrishtr, 2014/11/14 19:16:09]

Done.

+
 void ImagePainter::paintBoxDecorationBackground(PaintInfo& paintInfo, const LayoutPoint& paintOffset)
 {
     // Don't anti-alias the background of an image. See crbug.com/423834 for the reason why.
     // However, don't turn off anti-aliasing for subclasses such as video.
-    bool shouldAntialias = !m_renderImage.isRenderImage();
+    // An additional mega-hack here is to turn off anti-aliasing only for situations with a large device scale factor
+    // The referenced bug gives more details about a device with a scale factor greater than 3.4).
+    bool shouldAntialias = !m_renderImage.isRenderImage() || blink::deviceScaleFactor(m_renderImage.frame()) < 3.4;
 
     bool oldShouldAntialias = paintInfo.context->shouldAntialias();
-
     paintInfo.context->setShouldAntialias(shouldAntialias);
     BoxPainter(m_renderImage).paintBoxDecorationBackground(paintInfo, paintOffset);
+
     paintInfo.context->setShouldAntialias(oldShouldAntialias);
 }
 
 } // namespace blink