Basic use implementation for MediaStream from Canvas: captureStream()

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

Index: third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp b/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
index e04ea2b304f96f0bc3e3c80e013ff43918bbac47..08952acdae436450bb6d318ce56846109d988cbe 100644
--- a/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
@@ -283,6 +283,8 @@ void HTMLCanvasElement::didDraw(const FloatRect& rect)
 
 void HTMLCanvasElement::didFinalizeFrame()
 {
+    notifyListenersCanvasChanged();
+
     if (m_dirtyRect.isEmpty())
         return;
 
@@ -393,13 +395,30 @@ bool HTMLCanvasElement::paintsIntoCanvasBuffer() const
 
     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.
@@ -568,6 +587,17 @@ void HTMLCanvasElement::toBlob(FileCallback* callback, const String& mimeType, c
     }
 }
 
+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();
@@ -743,6 +773,7 @@ void HTMLCanvasElement::notifySurfaceInvalid()
 
 DEFINE_TRACE(HTMLCanvasElement)
 {
+    visitor->trace(m_listeners);
     visitor->trace(m_context);
     DocumentVisibilityObserver::trace(visitor);
     HTMLElement::trace(visitor);