Removing the dependency on GraphicsContext for drawing images in 2D canvas

Source/platform/graphics/CrossfadeGeneratedImage.cpp

 /*
  * Copyright (C) 2011 Apple 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 22 matching lines @@
 
 CrossfadeGeneratedImage::CrossfadeGeneratedImage(Image* fromImage, Image* toImage, float percentage, IntSize crossfadeSize, const IntSize& size)
     : GeneratedImage(size)
     , m_fromImage(fromImage)
     , m_toImage(toImage)
     , m_percentage(percentage)
     , m_crossfadeSize(crossfadeSize)
 {
 }
 
-void CrossfadeGeneratedImage::drawCrossfade(GraphicsContext* context, SkXfermode::Mode xferMode)
+void CrossfadeGeneratedImage::drawCrossfade(SkCanvas* canvas, const SkPaint& paint)
 {
-    float inversePercentage = 1 - m_percentage;
+    FloatRect fromImageRect(FloatPoint(), m_fromImage->size());
+    FloatRect toImageRect(FloatPoint(), m_toImage->size());
+    FloatRect destRect(FloatPoint(), m_crossfadeSize);
 
-    IntSize fromImageSize = m_fromImage->size();
-    IntSize toImageSize = m_toImage->size();
+    // TODO(junov): The various effects encoded into paint should probably be applied here
+    // instead of inside the layer.  This probably faulty behavior was maintained in order
+    // to preserve pre-existing behavior while refactoring this code.  This should be
+    // investigated further. crbug.com/472634
+    SkXfermode::Mode compositeOp;
+    if (!SkXfermode::AsMode(paint.getXfermode(), &compositeOp))
+        compositeOp = SkXfermode::kSrcOver_Mode;

[f(malita), 2015/04/17 16:18:32]

Nit: how about just

  layerPaint.setXfermode(paint.getXfermode())

+    SkPaint layerPaint;
+    layerPaint.setXfermodeMode(compositeOp);
+    canvas->saveLayer(nullptr, &layerPaint);
 
-    context->beginLayer(1, xferMode);
+    SkPaint imagePaint(paint);
+    imagePaint.setXfermodeMode(SkXfermode::kPlus_Mode);
+    imagePaint.setColor(scaleAlpha(SK_ColorBLACK, 1 - m_percentage));
+    // TODO(junov): This code should probably be propagating the RespectImageOrientationEnum
+    // form CrossfadeGeneratedImage::draw. Code was written this way during refactoring to
+    // avoid modifying existing behavior, but this warrants further investigation. crbug.com/472634
+    m_fromImage->draw(canvas, imagePaint, destRect, fromImageRect, DoNotRespectImageOrientation);
+    imagePaint.setColor(scaleAlpha(SK_ColorBLACK, m_percentage));
+    m_toImage->draw(canvas, imagePaint, destRect, toImageRect, DoNotRespectImageOrientation);
 
-    // Draw the image we're fading away from.
-    context->save();
-    if (m_crossfadeSize != fromImageSize) {
-        context->scale(
-            static_cast<float>(m_crossfadeSize.width()) / fromImageSize.width(),
-            static_cast<float>(m_crossfadeSize.height()) / fromImageSize.height());
-    }
-    context->setAlphaAsFloat(inversePercentage);
-    context->drawImage(m_fromImage, IntPoint());
-    context->restore();
-
-    // Draw the image we're fading towards.
-    context->save();
-    if (m_crossfadeSize != toImageSize) {
-        context->scale(
-            static_cast<float>(m_crossfadeSize.width()) / toImageSize.width(),
-            static_cast<float>(m_crossfadeSize.height()) / toImageSize.height());
-    }
-    context->setAlphaAsFloat(m_percentage);
-    context->drawImage(m_toImage, IntPoint(), SkXfermode::kPlus_Mode);
-    context->restore();
-
-    context->endLayer();
+    canvas->restore();

[f(malita), 2015/04/17 16:18:32]

Nit: use SkAutoCanvasRestore instead?

 }
 
-void CrossfadeGeneratedImage::draw(GraphicsContext* context, const FloatRect& dstRect, const FloatRect& srcRect, SkXfermode::Mode compositeOp, RespectImageOrientationEnum)
+void CrossfadeGeneratedImage::draw(SkCanvas* canvas, const SkPaint& paint, const FloatRect& dstRect, const FloatRect& srcRect, RespectImageOrientationEnum)
 {
     // Draw nothing if either of the images hasn't loaded yet.
     if (m_fromImage == Image::nullImage() || m_toImage == Image::nullImage())
         return;
 
-    GraphicsContextStateSaver stateSaver(*context);
-    context->clip(dstRect);
-    context->translate(dstRect.x(), dstRect.y());
+    canvas->save();

[f(malita), 2015/04/17 16:18:32]

Nit: same here

+    canvas->clipRect(dstRect);
+    canvas->translate(dstRect.x(), dstRect.y());
     if (dstRect.size() != srcRect.size())
-        context->scale(dstRect.width() / srcRect.width(), dstRect.height() / srcRect.height());
-    context->translate(-srcRect.x(), -srcRect.y());
+        canvas->scale(dstRect.width() / srcRect.width(), dstRect.height() / srcRect.height());
+    canvas->translate(-srcRect.x(), -srcRect.y());
 
-    drawCrossfade(context, compositeOp);
+    drawCrossfade(canvas, paint);
+    canvas->restore();
 }
 
 void CrossfadeGeneratedImage::drawTile(GraphicsContext* context, const FloatRect& srcRect)
 {
     // Draw nothing if either of the images hasn't loaded yet.
     if (m_fromImage == Image::nullImage() || m_toImage == Image::nullImage())
         return;
 
-    drawCrossfade(context, SkXfermode::kSrcOver_Mode);
+    SkPaint paint = context->fillPaint();
+    paint.setXfermodeMode(SkXfermode::kSrcOver_Mode);
+    drawCrossfade(context->canvas(), paint);
 }
 
 } // namespace blink