Correct color bleeding of no-repeat pattern in canvas2d

third_party/WebKit/Source/platform/graphics/ImagePattern.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 "platform/graphics/ImagePattern.h"
 
 #include "platform/graphics/Image.h"
 #include "platform/graphics/skia/SkiaUtils.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "third_party/skia/include/core/SkImage.h"
@@ skipping 31 matching lines @@
 
     // Skia does not have a "draw the tile only once" option. Clamp_TileMode
     // repeats the last line of the image after drawing one tile. To avoid
     // filling the space with arbitrary pixels, this workaround forces the
     // image to have a line of transparent pixels on the "repeated" edge(s),
     // thus causing extra space to be transparent filled.
     SkShader::TileMode tileModeX = isRepeatX()
         ? SkShader::kRepeat_TileMode : SkShader::kClamp_TileMode;
     SkShader::TileMode tileModeY = isRepeatY()
         ? SkShader::kRepeat_TileMode : SkShader::kClamp_TileMode;
     int expandW = isRepeatX() ? 0 : 1;

[Justin Novosad, 2016/07/08 19:17:01]

put 2 here to avoid multiplication later

     int expandH = isRepeatY() ? 0 : 1;
 
     // Create a transparent image 1 pixel wider and/or taller than the
     // original, then copy the orignal into it.
     // FIXME: Is there a better way to pad (not scale) an image in skia?
     sk_sp<SkSurface> surface = SkSurface::MakeRasterN32Premul(
-        m_tileImage->width() + expandW, m_tileImage->height() + expandH);
+        m_tileImage->width() + expandW * 2, m_tileImage->height() + expandH * 2);
     if (!surface)
         return SkShader::MakeColorShader(SK_ColorTRANSPARENT);
 
     SkPaint paint;
     paint.setXfermodeMode(SkXfermode::kSrc_Mode);
     surface->getCanvas()->drawImage(m_tileImage, 0, 0, &paint);
 
-    return surface->makeImageSnapshot()->makeShader(tileModeX, tileModeY, &localMatrix);
+    SkMatrix newLocalMatrix(localMatrix);
+    newLocalMatrix.setTranslate((isRepeatX() ? 0 : -1), (isRepeatY() ? 0 : -1));
+    
+    return surface->makeImageSnapshot()->makeShader(tileModeX, tileModeY, &newLocalMatrix);
 }
 
 bool ImagePattern::isTextureBacked() const
 {
     return m_tileImage && m_tileImage->isTextureBacked();
 }
 
 } // namespace blink