Fixed Shadow blur for transparent objects

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 33 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/SkPictureRecorder.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/SkDropShadowImageFilter.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"
 
 namespace {
 
@@ skipping 255 matching lines @@
         }
         clearShadow();
         return;
     }
 
     drawLooperBuilder->addShadow(offset, blur, color, shadowTransformMode, shadowAlphaMode);
     if (shadowMode == DrawShadowAndForeground) {
         drawLooperBuilder->addUnmodifiedContent();
     }
     setDrawLooper(drawLooperBuilder.release());
+
+    if (shadowMode == DrawShadowAndForeground
+        && shadowTransformMode == DrawLooperBuilder::ShadowIgnoresTransforms
+        && shadowAlphaMode == DrawLooperBuilder::ShadowRespectsAlpha) {
+        // This image filter will only be used to replace the drawLooper created above if the image is not opaque

[Stephen White, 2014/10/23 19:08:49]

Nit: "the image" here suggests we're always drawing an image. Suggest "will be
used in place of the drawLooper created above but only for drawing non-opaque
bitmaps; see preparePaintForDrawRectToRect()."

[sugoi1, 2014/10/23 20:25:14]

Done.

+        SkColor skColor = color.rgb();
+        const SkScalar sigma = 0.288675f * blur + 0.5f;

[Stephen White, 2014/10/23 19:08:49]

Nit: add a comment describing the origin of this constant (can just mention that
it's in the blurmaskfilter, if you like).

[sugoi1, 2014/10/23 20:25:14]

Done.

+        RefPtr<SkImageFilter> filter = adoptRef(SkDropShadowImageFilter::Create(offset.width(), offset.height(), sigma, sigma, skColor));
+        setDropShadowImageFilter(filter);
+    }
 }
 
 void GraphicsContext::setDrawLooper(PassOwnPtr<DrawLooperBuilder> drawLooperBuilder)
 {
     if (contextDisabled())
         return;
 
     mutableState()->setDrawLooper(drawLooperBuilder->detachDrawLooper());
 }
 
 void GraphicsContext::clearDrawLooper()
 {
     if (contextDisabled())
         return;
 
     mutableState()->clearDrawLooper();
 }
 
+void GraphicsContext::setDropShadowImageFilter(PassRefPtr<SkImageFilter> imageFilter)
+{
+    if (contextDisabled())
+        return;
+
+    mutableState()->setDropShadowImageFilter(imageFilter);
+}
+
+void GraphicsContext::clearDropShadowImageFilter()
+{
+    if (contextDisabled())
+        return;
+
+    mutableState()->clearDropShadowImageFilter();
+}
+
 bool GraphicsContext::hasShadow() const
 {
-    return !!immutableState()->drawLooper();
+    return !!immutableState()->drawLooper() || !!immutableState()->dropShadowImageFilter();
 }
 
 bool GraphicsContext::getTransformedClipBounds(FloatRect* bounds) const
 {
     if (contextDisabled())
         return false;
     ASSERT(m_canvas);
     SkIRect skIBounds;
     if (!m_canvas->getClipDeviceBounds(&skIBounds))
         return false;
@@ skipping 1600 matching lines @@
         m_textRegion.join(textRect);
     }
 }
 
 void GraphicsContext::preparePaintForDrawRectToRect(
     SkPaint* paint,
     const SkRect& srcRect,
     const SkRect& destRect,
     CompositeOperator compositeOp,
     WebBlendMode blendMode,
+    bool isOpaque,

[Justin Novosad, 2014/10/23 17:59:22]

bikeshed: For readability it should be clear that this argument is just for
bitmaps.  You can't call it isOpaqueBitmap, because that does not correctly
express what you are doing here. isNotNonOpaqueBitmap would be accurate, but the
double negative is gross. I would invert it semantics, so that you can call it
isNonOpaqueBitmap, and get rid of the '!' below.

[sugoi1, 2014/10/23 20:25:14]

Done.

     bool isLazyDecoded,
     bool isDataComplete) const
 {
     paint->setXfermodeMode(WebCoreCompositeToSkiaComposite(compositeOp, blendMode));
     paint->setColorFilter(this->colorFilter());
     paint->setAlpha(this->getNormalizedAlpha());
-    paint->setLooper(this->drawLooper());
+    if (this->dropShadowImageFilter() && !isOpaque) {

[Stephen White, 2014/10/23 19:08:49]

I was about to say we don't use "this->" in Blink code, but I see the rest of
this function already has it. Leave it in for now, and we'll remove them all in
a subsequent CL.

[sugoi1, 2014/10/23 20:25:14]

Acknowledged.

+        paint->setImageFilter(this->dropShadowImageFilter());
+    } else {
+        paint->setLooper(this->drawLooper());
+    }
     paint->setAntiAlias(shouldDrawAntiAliased(this, destRect));
 
     InterpolationQuality resampling;
     if (this->isAccelerated()) {
         resampling = InterpolationLow;
     } else if (this->printing()) {
         resampling = InterpolationNone;
     } else if (isLazyDecoded) {
         resampling = InterpolationHigh;
     } else {
@@ skipping 13 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));
 }
 
 } // namespace blink