Correct color bleeding of no-repeat pattern in canvas2d

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

Index: third_party/WebKit/Source/platform/graphics/ImagePattern.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/ImagePattern.cpp b/third_party/WebKit/Source/platform/graphics/ImagePattern.cpp
index 7decc3076d51b8801bba501abae5f31b8111bb41..2f65eaae0fc18a122082a6755244d86c841f3c1b 100644
--- a/third_party/WebKit/Source/platform/graphics/ImagePattern.cpp
+++ b/third_party/WebKit/Source/platform/graphics/ImagePattern.cpp
@@ -49,22 +49,25 @@ sk_sp<SkShader> ImagePattern::createShader(const SkMatrix& localMatrix) const
         ? SkShader::kRepeat_TileMode : SkShader::kClamp_TileMode;
     SkShader::TileMode tileModeY = isRepeatY()
         ? SkShader::kRepeat_TileMode : SkShader::kClamp_TileMode;
-    int expandW = isRepeatX() ? 0 : 1;
-    int expandH = isRepeatY() ? 0 : 1;
+    int borderPixelX = isRepeatX() ? 0 : 1;
+    int borderPixelY = isRepeatY() ? 0 : 1;
 
-    // Create a transparent image 1 pixel wider and/or taller than the
-    // original, then copy the orignal into it.
+    // Create a transparent image 2 pixels wider and/or taller than the
+    // original, then copy the orignal into the middle of 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() + borderPixelX * 2, m_tileImage->height() + borderPixelY * 2);

[Justin Novosad, 2016/07/08 19:17:02]

Nit: in polynomial terms, the convention is to put the coefficient first (2 *
borderPixelX) 

     if (!surface)
         return SkShader::MakeColorShader(SK_ColorTRANSPARENT);
 
     SkPaint paint;
     paint.setXfermodeMode(SkXfermode::kSrc_Mode);
-    surface->getCanvas()->drawImage(m_tileImage, 0, 0, &paint);
+    surface->getCanvas()->drawImage(m_tileImage, borderPixelX, borderPixelY, &paint);
 
-    return surface->makeImageSnapshot()->makeShader(tileModeX, tileModeY, &localMatrix);
+    SkMatrix newLocalMatrix(localMatrix);
+    newLocalMatrix.postTranslate(-1 * borderPixelX, -1 * borderPixelY);

[Justin Novosad, 2016/07/08 19:17:02]

nit : use unary minus (-borderPixelX)

+
+    return surface->makeImageSnapshot()->makeShader(tileModeX, tileModeY, &newLocalMatrix);
 }
 
 bool ImagePattern::isTextureBacked() const