Avoid non-opaque->opaque requests to SkCanvas::writePixels()

third_party/WebKit/Source/platform/graphics/ImageBuffer.cpp

 /*
  * Copyright (c) 2008, Google Inc. All rights reserved.
  * Copyright (C) 2009 Dirk Schulze <krit@webkit.org>
  * 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:
  *
  *     * Redistributions of source code must retain the above copyright
@@ skipping 449 matching lines @@
   int originY = sourceRect.y();
   int destY = destPoint.y() + sourceRect.y();
   DCHECK_GE(destY, 0);
   DCHECK_LT(destY, m_surface->size().height());
   DCHECK_GE(originY, 0);
   DCHECK_LT(originY, sourceRect.maxY());
 
   const size_t srcBytesPerRow = bytesPerPixel * sourceSize.width();
   const void* srcAddr =
       source + originY * srcBytesPerRow + originX * bytesPerPixel;
-  SkAlphaType alphaType = (multiplied == Premultiplied) ? kPremul_SkAlphaType
-                                                        : kUnpremul_SkAlphaType;
+
+  SkAlphaType alphaType;
+  if (Opaque == m_surface->getOpacityMode()) {
+    // If the surface is opaque, tell it that we are writing opaque
+    // pixels.  Writing non-opaque pixels to opaque is undefined in
+    // Skia.  There is some discussion about whether it should be
+    // defined in skbug.com/6157.  For now, we can get the desired
+    // behavior (memcpy) by pretending the write is opaque.
+    alphaType = kOpaque_SkAlphaType;
+  } else {
+    alphaType = (multiplied == Premultiplied) ? kPremul_SkAlphaType
+                                              : kUnpremul_SkAlphaType;
+  }
+
   SkImageInfo info;
   if (m_surface->colorSpace()) {
     info = SkImageInfo::Make(sourceRect.width(), sourceRect.height(),
                              m_surface->colorType(), alphaType,
                              m_surface->colorSpace());
   } else {
     info = SkImageInfo::Make(
         sourceRect.width(), sourceRect.height(), kRGBA_8888_SkColorType,
         alphaType, SkColorSpace::MakeNamed(SkColorSpace::kSRGB_Named));
   }
@@ skipping 115 matching lines @@
   DCHECK(MIMETypeRegistry::isSupportedImageMIMETypeForEncoding(mimeType));
 
   Vector<unsigned char> result;
   if (!encodeImage(mimeType, quality, &result))
     return "data:,";
 
   return "data:" + mimeType + ";base64," + base64Encode(result);
 }
 
 }  // namespace blink