2D canvas: fix shadow rendering with compositing modes that require temp layers

Source/core/html/canvas/CanvasRenderingContext2D.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008 Dirk Schulze <krit@webkit.org>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  * Copyright (C) 2012, 2013 Intel Corporation. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
@@ skipping 1393 matching lines @@
     bool wasDrawingShadows = shouldDrawShadows();
     realizeSaves(0);
     modifiableState().m_shadowOffset = offset;
     modifiableState().m_shadowBlur = blur;
     modifiableState().m_shadowColor = color;
     if (!wasDrawingShadows && !shouldDrawShadows())
         return;
     applyShadow();
 }
 
-void CanvasRenderingContext2D::applyShadow()
+void CanvasRenderingContext2D::applyShadow(ShadowMode shadowMode)
 {
     GraphicsContext* c = drawingContext();
     if (!c)
         return;
 
     if (shouldDrawShadows()) {
         c->setShadow(state().m_shadowOffset, state().m_shadowBlur, state().m_shadowColor,
-            DrawLooperBuilder::ShadowIgnoresTransforms);
+            DrawLooperBuilder::ShadowIgnoresTransforms, DrawLooperBuilder::ShadowRespectsAlpha, shadowMode);
     } else {
         c->clearShadow();
     }
 }
 
 bool CanvasRenderingContext2D::shouldDrawShadows() const
 {
     return alphaChannel(state().m_shadowColor) && (state().m_shadowBlur || !state().m_shadowOffset.isZero());
 }
 
@@ skipping 206 matching lines @@
 {
     context->fillPath(path);
 }
 
 template<class T> void CanvasRenderingContext2D::fullCanvasCompositedFill(const T& area)
 {
     ASSERT(isFullCanvasCompositeMode(state().m_globalComposite));
 
     GraphicsContext* c = drawingContext();
     ASSERT(c);
+
+    CompositeOperator previousOperator = c->compositeOperation();
+    if (shouldDrawShadows()) {
+        // unroll into two independently composited passes if drawing shadows
+        c->beginLayer(1, state().m_globalComposite);
+        c->setCompositeOperation(CompositeSourceOver);
+        applyShadow(DrawShadowOnly);
+        fillPrimitive(area, c);
+        c->setCompositeOperation(previousOperator);
+        c->endLayer();
+    }
+
     c->beginLayer(1, state().m_globalComposite);
-    CompositeOperator previousOperator = c->compositeOperation();
+    applyShadow(DrawForegroundOnly);
     c->setCompositeOperation(CompositeSourceOver);
     fillPrimitive(area, c);
     c->setCompositeOperation(previousOperator);
     c->endLayer();
+    applyShadow(DrawShadowAndForeground); // go back to normal shadows
 }
 
 static void strokePrimitive(const FloatRect& rect, GraphicsContext* context)
 {
     context->strokeRect(rect);
 }
 
 static void strokePrimitive(const Path& path, GraphicsContext* context)
 {
     context->strokePath(path);
 }
 
 template<class T> void CanvasRenderingContext2D::fullCanvasCompositedStroke(const T& area)
 {
     ASSERT(isFullCanvasCompositeMode(state().m_globalComposite));
 
     GraphicsContext* c = drawingContext();
     ASSERT(c);
+
+    CompositeOperator previousOperator = c->compositeOperation();
+    if (shouldDrawShadows()) {
+        // unroll into two independently composited passes if drawing shadows
+        c->beginLayer(1, state().m_globalComposite);
+        c->setCompositeOperation(CompositeSourceOver);
+        applyShadow(DrawShadowOnly);
+        strokePrimitive(area, c);
+        c->setCompositeOperation(previousOperator);
+        c->endLayer();
+    }
+
     c->beginLayer(1, state().m_globalComposite);
-    CompositeOperator previousOperator = c->compositeOperation();
+    applyShadow(DrawForegroundOnly);
     c->setCompositeOperation(CompositeSourceOver);
     strokePrimitive(area, c);
     c->setCompositeOperation(previousOperator);
     c->endLayer();
+    applyShadow(DrawShadowAndForeground); // go back to normal shadows
 }
 
 PassRefPtrWillBeRawPtr<CanvasGradient> CanvasRenderingContext2D::createLinearGradient(float x0, float y0, float x1, float y1)
 {
     RefPtrWillBeRawPtr<CanvasGradient> gradient = CanvasGradient::create(FloatPoint(x0, y0), FloatPoint(x1, y1));
     return gradient.release();
 }
 
 PassRefPtrWillBeRawPtr<CanvasGradient> CanvasRenderingContext2D::createRadialGradient(float x0, float y0, float r0, float x1, float y1, float r1, ExceptionState& exceptionState)
 {
@@ skipping 774 matching lines @@
 
 unsigned CanvasRenderingContext2D::hitRegionsCount() const
 {
     if (m_hitRegionManager)
         return m_hitRegionManager->getHitRegionsCount();
 
     return 0;
 }
 
 } // namespace blink