Fix the rasterization resolution of zoomed canvases with display list backing

Source/platform/graphics/GraphicsContext.cpp

 /*
  * Copyright (C) 2003, 2004, 2005, 2006, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 32 matching lines @@
 #include "third_party/skia/include/core/SkColorFilter.h"
 #include "third_party/skia/include/core/SkData.h"
 #include "third_party/skia/include/core/SkDevice.h"
 #include "third_party/skia/include/core/SkPicture.h"
 #include "third_party/skia/include/core/SkRRect.h"
 #include "third_party/skia/include/core/SkRefCnt.h"
 #include "third_party/skia/include/core/SkSurface.h"
 #include "third_party/skia/include/effects/SkBlurMaskFilter.h"
 #include "third_party/skia/include/effects/SkCornerPathEffect.h"
 #include "third_party/skia/include/effects/SkLumaColorFilter.h"
+#include "third_party/skia/include/effects/SkMatrixImageFilter.h"
+#include "third_party/skia/include/effects/SkPictureImageFilter.h"
 #include "third_party/skia/include/gpu/GrRenderTarget.h"
 #include "third_party/skia/include/gpu/GrTexture.h"
 #include "wtf/Assertions.h"
 #include "wtf/MathExtras.h"
 
 using namespace std;
 using blink::WebBlendMode;
 
 namespace blink {
 
@@ skipping 1041 matching lines @@
         return;
 
     image->draw(this, dest, src, op, blendMode);
 }
 
 void GraphicsContext::drawPicture(PassRefPtr<SkPicture> picture, const FloatRect& dest, const FloatRect& src, CompositeOperator op, WebBlendMode blendMode)
 {
     if (contextDisabled() || !picture)
         return;
 
+    SkMatrix ctm = m_canvas->getTotalMatrix();
+    SkRect deviceDest;
+    ctm.mapRect(&deviceDest, dest);
+    SkRect sourceBounds = WebCoreFloatRectToSKRect(src);
+
+    RefPtr<SkPictureImageFilter> pictureFilter = adoptRef(SkPictureImageFilter::Create(picture.get(), sourceBounds));
+    SkMatrix layerScale;
+    layerScale.setScale(deviceDest.width() / src.width(), deviceDest.height() / src.height());
+    RefPtr<SkMatrixImageFilter> matrixFilter = adoptRef(SkMatrixImageFilter::Create(layerScale, SkPaint::kLow_FilterLevel, pictureFilter.get()));

[Stephen White, 2014/08/13 21:26:50]

Perf note: using a matrix filter will incur one extra (non-scaling) blit than
the old path. I'm not sure if this will show up in benches, but it's something
to think about. Maybe we could ameliorate it by having a way in Skia for the
final filter in the DAG to take on the responsibility of the blit, instead of
targeting its own internal buffer. This would be a perf win for all filters.

     SkPaint picturePaint;
     picturePaint.setXfermode(WebCoreCompositeToSkiaComposite(op, blendMode).get());
-    SkRect skBounds = WebCoreFloatRectToSKRect(dest);
-    saveLayer(&skBounds, &picturePaint);
-    SkMatrix pictureTransform;
-    pictureTransform.setRectToRect(WebCoreFloatRectToSKRect(src), skBounds, SkMatrix::kFill_ScaleToFit);
-    m_canvas->concat(pictureTransform);
-    picture->draw(m_canvas);
-    restoreLayer();
+    picturePaint.setImageFilter(matrixFilter.get());
+    SkRect layerBounds = SkRect::MakeWH(max(deviceDest.width(), sourceBounds.width()), max(deviceDest.height(), sourceBounds.height()));
+    m_canvas->save();
+    m_canvas->resetMatrix();
+    m_canvas->translate(deviceDest.x(), deviceDest.y());
+    m_canvas->saveLayer(&layerBounds, &picturePaint);
+    m_canvas->restore();
+    m_canvas->restore();
 }
 
 void GraphicsContext::writePixels(const SkImageInfo& info, const void* pixels, size_t rowBytes, int x, int y)
 {
     if (contextDisabled())
         return;
 
     m_canvas->writePixels(info, pixels, rowBytes, x, y);
 
     if (regionTrackingEnabled()) {
@@ skipping 805 matching lines @@
         // FIXME: This is to not break tests (it results in the filter bitmap flag
         // being set to true). We need to decide if we respect InterpolationNone
         // being returned from computeInterpolationQuality.
         resampling = InterpolationLow;
     }
     resampling = limitInterpolationQuality(this, resampling);
     paint->setFilterLevel(static_cast<SkPaint::FilterLevel>(resampling));
 }
 
 }