Implement WebGL's commit on the main thread

third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.cpp

 /*
  * Copyright (C) 2009 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 631 matching lines @@
     shouldFailContextCreationForTesting = true;
 }
 
 ImageBitmap* WebGLRenderingContextBase::transferToImageBitmapBase()
 {
     if (!drawingBuffer())
         return nullptr;
     return ImageBitmap::create(drawingBuffer()->transferToStaticBitmapImage());
 }
 
+void WebGLRenderingContextBase::commit(ExceptionState& exceptionState)
+{
+    if (!getOffscreenCanvas()) {
+        exceptionState.throwDOMException(InvalidStateError, "No OffscreenCanvas exists, abort commit().");

[Justin Novosad, 2016/09/12 13:53:25]

Error message would be more readable like this "Commit() was called on a
rendering context that was no created from an OffscreenCanvas."

[xidachen, 2016/09/14 01:33:12]

Done.

+        return;
+    }
+    // no HTMLCanvas associated, thrown InvalidStateError
+    if (getOffscreenCanvas()->getAssociatedCanvasId() == -1) {
+        exceptionState.throwDOMException(InvalidStateError, "Commit() was called on a context whose OffscreenCanvas is not associated with a canvas element.");
+        return;
+    }
+    if (!drawingBuffer())
+        return;
+    getOffscreenCanvas()->getOrCreateFrameDispatcher()->dispatchFrame(drawingBuffer()->transferToStaticBitmapImage());

[Justin Novosad, 2016/09/12 13:53:25]

Race condition right here. The return value of
drawingBuffer()->transferToStaticBitmapImage() needs to be retained to prevent
the texture from being deleted before the browser consumes it. It should
probably be retained in the Dispatcher. The texture also needs to be locked
(read-only in the renderer) until the browser returns it holding on to it in
SkImage form should do the trick.  Another problem is that this code will not
work correctly if the webgl context was created with the "preserveDrawingBuffer:
true" context creation attribute. No need to fix the preserveDrawingBuffer issue
in this CL, but at least create a crbug and reference it in a TODO right here.

+}
+
 PassRefPtr<Image> WebGLRenderingContextBase::getImage(AccelerationHint hint, SnapshotReason reason) const
 {
     if (!drawingBuffer())
         return nullptr;
 
     drawingBuffer()->commit();
     IntSize size = clampedCanvasSize();
     OpacityMode opacityMode = creationAttributes().hasAlpha() ? NonOpaque : Opaque;
     std::unique_ptr<AcceleratedImageBufferSurface> surface = wrapUnique(new AcceleratedImageBufferSurface(size, opacityMode));
     if (!surface->isValid())
@@ skipping 5775 matching lines @@
 
 void WebGLRenderingContextBase::getHTMLOrOffscreenCanvas(HTMLCanvasElementOrOffscreenCanvas& result) const
 {
     if (canvas())
         result.setHTMLCanvasElement(canvas());
     else
         result.setOffscreenCanvas(getOffscreenCanvas());
 }
 
 } // namespace blink