Fixed Shadow blur for transparent objects

Source/platform/graphics/GraphicsContext.cpp

Index: Source/platform/graphics/GraphicsContext.cpp
diff --git a/Source/platform/graphics/GraphicsContext.cpp b/Source/platform/graphics/GraphicsContext.cpp
index 38d4105bd7b6f85283bc7d9e443f692781b8ef1a..cc3350a2215531796a67a14de8d8c4af33dedfdd 100644
--- a/Source/platform/graphics/GraphicsContext.cpp
+++ b/Source/platform/graphics/GraphicsContext.cpp
@@ -51,6 +51,7 @@
 #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"
@@ -326,6 +327,16 @@ void GraphicsContext::setShadow(const FloatSize& offset, float blur, const Color
         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)
@@ -344,9 +355,25 @@ void GraphicsContext::clearDrawLooper()
     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
@@ -1967,13 +1994,18 @@ void GraphicsContext::preparePaintForDrawRectToRect(
     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;