Fix unreliable MediaStream capture from WebGL canvases

third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp

 /*
  * Copyright (C) 2004, 2006, 2007 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. 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.
@@ skipping 311 matching lines @@
   } else {
     m_dirtyRect.unite(rect);
   }
   if (m_context && m_context->is2d() && hasImageBuffer())
     buffer()->didDraw(rect);
 }
 
 void HTMLCanvasElement::finalizeFrame() {
   if (hasImageBuffer())
     m_imageBuffer->finalizeFrame();
-  notifyListenersCanvasChanged();
+
+  // If the canvas is visible, notifying listeners is taken
+  // care of in the in doDeferredPaintInvalidation, which allows
+  // the frame to be grabbed prior to compositing, which is
+  // critically important because compositing may clear the canvas's
+  // image. (e.g. WebGL context with preserveDrawingBuffer=false).
+  // If the canvas is not visible, doDeferredPaintInvalidation
+  // will not get called, so we need to take care of business here.
+  if (!m_didNotifyListenersForCurrentFrame)
+    notifyListenersCanvasChanged();
+  m_didNotifyListenersForCurrentFrame = false;
 }
 
 void HTMLCanvasElement::didDisableAcceleration() {
   // We must force a paint invalidation on the canvas even if it's
   // content did not change because it layer was destroyed.
   didDraw(FloatRect(0, 0, size().width(), size().height()));
 }
 
 void HTMLCanvasElement::restoreCanvasMatrixClipStack(
     PaintCanvas* canvas) const {
@@ skipping 21 matching lines @@
       invalidationRect = m_dirtyRect;
     }
     if (hasImageBuffer()) {
       m_imageBuffer->doPaintInvalidation(invalidationRect);
     }
   }
 
   if (m_dirtyRect.isEmpty())
     return;
 
+  notifyListenersCanvasChanged();
+  m_didNotifyListenersForCurrentFrame = true;
+
   // Propagate the m_dirtyRect accumulated so far to the compositor
   // before restarting with a blank dirty rect.
   FloatRect srcRect(0, 0, size().width(), size().height());
 
   LayoutBox* ro = layoutBox();
   // Canvas content updates do not need to be propagated as
   // paint invalidations if the canvas is accelerated, since
   // the canvas contents are sent separately through a texture layer.
   if (ro && (!m_context || !m_context->isAccelerated())) {
     // If ro->contentBoxRect() is larger than srcRect the canvas's image is
@@ skipping 1072 matching lines @@
     // Creates a placeholder layer first before Surface is created.
     m_surfaceLayerBridge->createSolidColorLayer();
   }
 }
 
 void HTMLCanvasElement::OnWebLayerReplaced() {
   setNeedsCompositingUpdate();
 }
 
 }  // namespace blink