Change filter quality when scaling-down in drawImage

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

 // Copyright 2016 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 "modules/canvas2d/BaseRenderingContext2D.h"
 
 #include "bindings/core/v8/ExceptionMessages.h"
 #include "bindings/core/v8/ExceptionState.h"
 #include "bindings/core/v8/ExceptionStatePlaceholder.h"
 #include "core/css/parser/CSSParser.h"
@@ skipping 923 matching lines @@
     // discouraged. Always drawing with AA can negatively impact performance
     // though - that's why it's not always on.
     SkScalar widthExpansion, heightExpansion;
     if (ctm.getType() & SkMatrix::kAffine_Mask)
         widthExpansion = ctm[SkMatrix::kMSkewY], heightExpansion = ctm[SkMatrix::kMSkewX];
     else
         widthExpansion = ctm[SkMatrix::kMScaleX], heightExpansion = ctm[SkMatrix::kMScaleY];
     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();
+}
+
 void BaseRenderingContext2D::drawImageInternal(SkCanvas* c, CanvasImageSource* imageSource, Image* image, const FloatRect& srcRect, const FloatRect& dstRect, const SkPaint* paint)
 {
     trackDrawCall(DrawImage);
 
     int initialSaveCount = c->getSaveCount();
     SkPaint imagePaint = *paint;
 
     if (paint->getImageFilter()) {
         SkMatrix ctm = c->getTotalMatrix();
         SkMatrix invCtm;
@@ skipping 11 matching lines @@
         SkPaint layerPaint;
         layerPaint.setXfermode(sk_ref_sp(paint->getXfermode()));
         layerPaint.setImageFilter(paint->getImageFilter());
 
         c->saveLayer(&bounds, &layerPaint);
         c->concat(ctm);
         imagePaint.setXfermodeMode(SkXfermode::kSrcOver_Mode);
         imagePaint.setImageFilter(nullptr);
     }
 
+    if (!imageSmoothingEnabled() && isDrawScalingDown(srcRect, state().transform().mapRect(dstRect)))

[Justin Novosad, 2016/07/20 17:36:36]

Using mapRect is not correct.
For example if you scale by 0.9 and rotate by 45deg.  The image is being
scaled-down, but map rect s going to give you the bounding box of the tranformed
rect, which will be bigger than the original rect by a factor of 0.9*sqrt(2) =
1.27.

[xidachen, 2016/07/20 19:13:49]

Done.

+        imagePaint.setFilterQuality(kLow_SkFilterQuality);
+
     if (!imageSource->isVideoElement()) {
         imagePaint.setAntiAlias(shouldDrawImageAntialiased(dstRect));
         image->draw(c, imagePaint, dstRect, srcRect, DoNotRespectImageOrientation, Image::DoNotClampImageToSourceRect);
     } else {
         c->save();
         c->clipRect(dstRect);
         c->translate(dstRect.x(), dstRect.y());
         c->scale(dstRect.width() / srcRect.width(), dstRect.height() / srcRect.height());
         c->translate(-srcRect.x(), -srcRect.y());
         HTMLVideoElement* video = static_cast<HTMLVideoElement*>(imageSource);
@@ skipping 594 matching lines @@
     numPatterns(0),
     numDrawWithComplexClips(0),
     numBlurredShadows(0),
     numFilters(0),
     numGetImageDataCalls(0),
     numPutImageDataCalls(0),
     numClearRectCalls(0),
     numDrawFocusCalls(0) {}
 
 } // namespace blink