Fix box shadow rendering on opaque WebGL canvases

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp

 /*
  * Copyright (C) 2009, 2010, 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 373 matching lines @@
   if (shouldPaintOntoGraphicsLayer != !!m_backgroundPaintsOntoGraphicsLayer) {
     m_backgroundPaintsOntoGraphicsLayer = shouldPaintOntoGraphicsLayer;
     // The graphics layer needs to be updated for changed
     // m_backgroundPaintsOntoGraphicsLayer.
     m_graphicsLayer->setNeedsDisplay();
   }
 }
 
 void CompositedLayerMapping::updateContentsOpaque() {
   if (isAcceleratedCanvas(layoutObject())) {
-    // Determine whether the rendering context's external texture layer is
-    // opaque.
     CanvasRenderingContext* context =
         toHTMLCanvasElement(layoutObject()->node())->renderingContext();
-    if (!context->creationAttributes().alpha())
-      m_graphicsLayer->setContentsOpaque(true);
-    else if (WebLayer* layer = context->platformLayer())
-      m_graphicsLayer->setContentsOpaque(
-          !Color(layer->backgroundColor()).hasAlpha());
-    else
+    WebLayer* layer = context ? context->platformLayer() : nullptr;
+    // Determine whether the external texture layer covers the whole graphics
+    // layer. This may not be the case if there are box decorations or
+    // shadows.
+    if (layer &&
+        layer->bounds() == m_graphicsLayer->platformLayer()->bounds()) {
+      // Determine whether the rendering context's external texture layer is
+      // opaque.
+      if (!context->creationAttributes().alpha()) {
+        m_graphicsLayer->setContentsOpaque(true);
+      } else {
+        m_graphicsLayer->setContentsOpaque(
+            !Color(layer->backgroundColor()).hasAlpha());
+      }
+    } else {
       m_graphicsLayer->setContentsOpaque(false);
+    }
   } else if (m_backgroundLayer) {
     m_graphicsLayer->setContentsOpaque(false);
     m_backgroundLayer->setContentsOpaque(
         m_owningLayer.backgroundIsKnownToBeOpaqueInRect(compositedBounds()));
   } else {
     // For non-root layers, background is painted by the scrolling contents
     // layer if all backgrounds are background attachment local, otherwise
     // background is painted by the primary graphics layer.
     if (hasScrollingLayer() && m_backgroundPaintsOntoScrollingContentsLayer) {
       // Backgrounds painted onto the foreground are clipped by the padding box
@@ skipping 3029 matching lines @@
   } else if (graphicsLayer == m_decorationOutlineLayer.get()) {
     name = "Decoration Layer";
   } else {
     ASSERT_NOT_REACHED();
   }
 
   return name;
 }
 
 }  // namespace blink