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, double xScale, double yScale)
+{
+    return dstRect.width() * xScale < srcRect.width() && dstRect.height() * yScale < srcRect.height();

[Justin Novosad, 2016/07/20 19:43:56]

I had an idea: you can optimize out the expensive sqrt call inside xScale/yScale
by squaring both sides of the inequality.
The expression becomes: dstRect.width() * dstRect.width() * xScaleSquared <
srcRect.width() * srcRect.width()
Then you do the same for height.

The rects are stored in floats and the transform is in double.  The way it is
written now, the floats will be promoted to double in the expression. We wight
as well do all the arithmetic in float (like in the rest of the canvas
implementation), so you should make the args float.

[xidachen, 2016/07/20 20:31:33]

Done.

+}
+
 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, dstRect, state().transform().xScale(), state().transform().yScale()))
+        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