Basic use implementation for MediaStream from Canvas: captureStream()

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 265 matching lines @@
     clearCopiedImage();
     if (layoutObject())
         layoutObject()->setMayNeedPaintInvalidation();
     m_dirtyRect.unite(rect);
     if (m_context && m_context->is2d() && hasImageBuffer())
         buffer()->didDraw(rect);
 }
 
 void HTMLCanvasElement::didFinalizeFrame()
 {
+    notifyListenersCanvasChanged();
+
     if (m_dirtyRect.isEmpty())
         return;
 
     // 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());
     m_dirtyRect.intersect(srcRect);
     LayoutBox* ro = layoutBox();
     // Canvas content updates do not need to be propagated as
     // paint invalidations if the canvas is accelerated, since
@@ skipping 90 matching lines @@
         }
     }
 }
 
 bool HTMLCanvasElement::paintsIntoCanvasBuffer() const
 {
     ASSERT(m_context);
 
     if (!m_context->isAccelerated())
         return true;
-
     if (layoutBox() && layoutBox()->hasAcceleratedCompositing())
         return false;
 
     return true;
 }
 
+void HTMLCanvasElement::notifyListenersCanvasChanged()
+{
+    if (!originClean()) {
+        m_listeners.clear();
+        return;
+    }
+
+    for (CanvasDrawListener* listener : m_listeners) {
+        if (listener->needsNewFrameCapture()) {
+            SourceImageStatus status;
+            RefPtr<Image> sourceImage = getSourceImageForCanvas(&status, PreferNoAcceleration);

[esprehn, 2015/12/01 20:04:26]

getSourceImageForCanvas is expensive I think it seems to contain GPU readback
code paths, I don't think you want to do it for each loop iteration. I think you
want to loop through the list first to see if any listeners have
needsNewFrameCapture true, then loop through again doing setNewFrameCapture(...)

[emircan, 2015/12/01 21:07:34]

Done. My bad, I was initially designing it with a single listener in mind.

+            if (status != NormalSourceImageStatus)
+                return;
+            listener->setNewFrameCapture(sourceImage->imageForCurrentFrame());
+        }
+    }
+}
+
 void HTMLCanvasElement::paint(GraphicsContext* context, const LayoutRect& r)
 {
     // FIXME: crbug.com/438240; there is a bug with the new CSS blending and compositing feature.
     if (!m_context)
         return;
     if (!paintsIntoCanvasBuffer() && !document().printing())
         return;
 
     m_context->paintRenderingResultsToCanvas(FrontBuffer);
     if (hasImageBuffer()) {
@@ skipping 148 matching lines @@
     RefPtr<DOMUint8ClampedArray> imageDataRef(imageData->data());
 
     RefPtr<CanvasAsyncBlobCreator> asyncCreatorRef = CanvasAsyncBlobCreator::create(imageDataRef.release(), encodingMimeType, imageData->size(), callback);
     if (Platform::current()->isThreadedCompositingEnabled() && (encodingMimeType == DefaultMimeType)) {
         asyncCreatorRef->scheduleAsyncBlobCreation(true);
     } else {
         asyncCreatorRef->scheduleAsyncBlobCreation(false, quality);
     }
 }
 
+void HTMLCanvasElement::addListener(CanvasDrawListener* listener)
+{
+    m_listeners.add(listener);
+    notifyListenersCanvasChanged();

[esprehn, 2015/12/01 20:04:26]

hmm, this means we do a sync readback the first time we add a listener, that
doesn't seem like a good idea

[emircan, 2015/12/01 21:07:34]

I see that frame might not be completed. I was trying to cut down the time on
black frame until next draw happens. I can bring that to the spec discussion.
Removed it. 

+}
+
+void HTMLCanvasElement::removeListener(CanvasDrawListener* listener)
+{
+    m_listeners.remove(listener);
+}
+
 SecurityOrigin* HTMLCanvasElement::securityOrigin() const
 {
     return document().securityOrigin();
 }
 
 bool HTMLCanvasElement::originClean() const
 {
     if (document().settings() && document().settings()->disableReadingFromCanvas())
         return false;
     return m_originClean;
@@ skipping 155 matching lines @@
 }
 
 void HTMLCanvasElement::notifySurfaceInvalid()
 {
     if (m_context && m_context->is2d())
         m_context->loseContext(CanvasRenderingContext::RealLostContext);
 }
 
 DEFINE_TRACE(HTMLCanvasElement)
 {
+    visitor->trace(m_listeners);
     visitor->trace(m_context);
     DocumentVisibilityObserver::trace(visitor);
     HTMLElement::trace(visitor);
 }
 
 void HTMLCanvasElement::updateExternallyAllocatedMemory() const
 {
     int bufferCount = 0;
     if (m_imageBuffer) {
         bufferCount++;
@@ skipping 196 matching lines @@
     }
     return ImageBitmapSource::fulfillImageBitmap(scriptState, isPaintable() ? ImageBitmap::create(this, IntRect(sx, sy, sw, sh)) : nullptr);
 }
 
 bool HTMLCanvasElement::isOpaque() const
 {
     return m_context && !m_context->hasAlpha();
 }
 
 } // blink