Determine if OffscreenCanvas is paintable in different rendering contexts

third_party/WebKit/Source/platform/graphics/skia/SkiaUtils.h

 /*
  * Copyright (c) 2006,2007,2008, 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 30 matching lines @@
 #include "third_party/skia/include/core/SkColor.h"
 #include "third_party/skia/include/core/SkRefCnt.h"
 #include "third_party/skia/include/core/SkScalar.h"
 #include "third_party/skia/include/core/SkXfermode.h"
 #include "wtf/MathExtras.h"
 
 namespace blink {
 
 class GraphicsContext;
 
+/**** constants ****/
+
+// 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 PLATFORM_EXPORT MaxCanvasArea = 32768 * 8192; // Maximum canvas area in CSS pixels

[Justin Novosad, 2016/08/19 17:30:01]

Defining a const in a header can lead to symbol clashes, we use "extern" to
avois this.  But that is moot anyways: the style guide encourages the use of
enums for integer constants.  And we now us a "k" prefix.  Just use an anonymous
enum, like this.

enum {
    kMaxCanvasArea = 32768 * 8192,
    kMaxSkiaDim = 32767
}

[xlai (Olivia), 2016/08/19 17:42:03]

Done.

+
+// In Skia, we will also limit width/height to 32767.
+const int PLATFORM_EXPORT MaxSkiaDim = 32767; // Maximum width/height in CSS pixels.
+
 SkXfermode::Mode PLATFORM_EXPORT WebCoreCompositeToSkiaComposite(CompositeOperator, WebBlendMode = WebBlendModeNormal);
 CompositeOperator PLATFORM_EXPORT compositeOperatorFromSkia(SkXfermode::Mode);
 WebBlendMode PLATFORM_EXPORT blendModeFromSkia(SkXfermode::Mode);
 
 // Map alpha values from [0, 1] to [0, 256] for alpha blending.
 int PLATFORM_EXPORT clampedAlphaForBlending(float);
 
 // Multiply a color's alpha channel by an additional alpha factor where
 // alpha is in the range [0, 1].
 SkColor PLATFORM_EXPORT scaleAlpha(SkColor, float);
@@ skipping 142 matching lines @@
 }
 
 template <typename T> sk_sp<T> toSkSp(const RefPtr<T>& ref)
 {
     return toSkSp(PassRefPtr<T>(ref));
 }
 
 } // namespace blink
 
 #endif  // SkiaUtils_h