Change filter quality when scaling-down in drawImage

third_party/WebKit/Source/modules/canvas2d/BaseRenderingContext2D.cpp

Index: third_party/WebKit/Source/modules/canvas2d/BaseRenderingContext2D.cpp
diff --git a/third_party/WebKit/Source/modules/canvas2d/BaseRenderingContext2D.cpp b/third_party/WebKit/Source/modules/canvas2d/BaseRenderingContext2D.cpp
index 2029de6d7d7f812aa189ca4529e5031003f1e253..60bd90ac4b574fdfe7f0e1d2bc7ce7cbecc592a6 100644
--- a/third_party/WebKit/Source/modules/canvas2d/BaseRenderingContext2D.cpp
+++ b/third_party/WebKit/Source/modules/canvas2d/BaseRenderingContext2D.cpp
@@ -941,6 +941,11 @@ bool BaseRenderingContext2D::shouldDrawImageAntialiased(const FloatRect& destRec
     return destRect.width() * fabs(widthExpansion) < 1 || destRect.height() * fabs(heightExpansion) < 1;
 }
 
+static bool isDrawScalingDown(const FloatRect& srcRect, const FloatRect& dstRect)
+{
+    return dstRect.width() < srcRect.width() && dstRect.height() < srcRect.height();

[Justin Novosad, 2016/07/19 17:17:16]

This is not good enough. You also have to take into account the transform
matrix. An the test need to cover cases like rotation+scale correctly.

[xidachen, 2016/07/20 11:16:02]

Done.

+}
+
 void BaseRenderingContext2D::drawImageInternal(SkCanvas* c, CanvasImageSource* imageSource, Image* image, const FloatRect& srcRect, const FloatRect& dstRect, const SkPaint* paint)
 {
     trackDrawCall(DrawImage);
@@ -972,6 +977,9 @@ void BaseRenderingContext2D::drawImageInternal(SkCanvas* c, CanvasImageSource* i
         imagePaint.setImageFilter(nullptr);
     }
 
+    if (!imageSmoothingEnabled() && isDrawScalingDown(srcRect, dstRect))
+        imagePaint.setFilterQuality(kLow_SkFilterQuality);
+
     if (!imageSource->isVideoElement()) {
         imagePaint.setAntiAlias(shouldDrawImageAntialiased(dstRect));
         image->draw(c, imagePaint, dstRect, srcRect, DoNotRespectImageOrientation, Image::DoNotClampImageToSourceRect);