Draw thin slices of an image w/ anti-aliasing for 2D <canvas>

Source/platform/graphics/GraphicsContext.h

 /*
  * Copyright (C) 2003, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2008-2009 Torch Mobile, Inc.
  * Copyright (C) 2013 Google 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.
@@ skipping 118 matching lines @@
 
     SkDrawLooper* drawLooper() const { return immutableState()->drawLooper(); }
 
     FloatRect getClipBounds() const;
     bool getTransformedClipBounds(FloatRect* bounds) const;
     SkMatrix getTotalMatrix() const;
 
     void setShouldAntialias(bool antialias) { mutableState()->setShouldAntialias(antialias); }
     bool shouldAntialias() const { return immutableState()->shouldAntialias(); }
 
+    // Disable the optimization that disables anti-aliasing for

[Justin Novosad, 2014/04/01 17:02:01]

Double negation: Disabling the disabling is more confusing than necessary.
Also, there should be some warning that determining whether an image is hairline
is only reliable when the device pixel scale is fixed (e.g. when drawing to an
ImageBuffer).  Therefore, this option should not be used on GraphicsContexts
that are backed by a recording canvas.  You could even add a safety check:
ASSERT(!isRecording());

[fs, 2014/04/02 08:31:37]

Made this read more like the name of the method.
Added a "Note" and the ASSERT.

+    // scale/multiple-of-90-degrees rotation for thin ("hairline") images.
+    void disableAntialiasingOptimizationForHairlineImages() { m_antialiasHairlineImages = true; }
+    bool shouldAntialiasHairlineImages() const { return m_antialiasHairlineImages; }
+
     void setShouldClampToSourceRect(bool clampToSourceRect) { mutableState()->setShouldClampToSourceRect(clampToSourceRect); }
     bool shouldClampToSourceRect() const { return immutableState()->shouldClampToSourceRect(); }
 
     void setShouldSmoothFonts(bool smoothFonts) { mutableState()->setShouldSmoothFonts(smoothFonts); }
     bool shouldSmoothFonts() const { return immutableState()->shouldSmoothFonts(); }
 
     // Turn off LCD text for the paint if not supported on this context.
     void adjustTextRenderMode(SkPaint*);
     bool couldUseLCDRenderedText();
 
@@ skipping 348 matching lines @@
     bool m_trackTextRegion : 1;
     SkRect m_textRegion;
 
     // Are we on a high DPI display? If so, spelling and grammar markers are larger.
     bool m_useHighResMarker : 1;
     // FIXME: Make this go away: crbug.com/236892
     bool m_updatingControlTints : 1;
     bool m_accelerated : 1;
     bool m_isCertainlyOpaque : 1;
     bool m_printing : 1;
+    bool m_antialiasHairlineImages : 1;
 };
 
 } // namespace WebCore
 
 #endif // GraphicsContext_h