Prime the landing pad for the new video rendering pipeline.

media/blink/video_frame_compositor.h

Index: media/blink/video_frame_compositor.h
diff --git a/media/blink/video_frame_compositor.h b/media/blink/video_frame_compositor.h
index 9e46663e34f74ef3d51ba96269b03addac9259f2..80b7e8e0aef5c706f4b93ce1bc34a912567bbd08 100644
--- a/media/blink/video_frame_compositor.h
+++ b/media/blink/video_frame_compositor.h
@@ -7,24 +7,41 @@
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
+#include "base/single_thread_task_runner.h"
+#include "base/synchronization/lock.h"
 #include "cc/layers/video_frame_provider.h"
 #include "media/base/media_export.h"
+#include "media/base/video_renderer_sink.h"
 #include "ui/gfx/geometry/size.h"
 
 namespace media {
 class VideoFrame;
 
-// VideoFrameCompositor handles incoming frames by notifying the compositor and
-// dispatching callbacks when detecting changes in video frames.
+// VideoFrameCompositor acts as a bridge between the media and compositor for
+// rendering video frames. I.e. a media::VideoRenderer will talk to this class
+// from the media side, while a cc::VideoFrameProvider::Client will talk to it
+// from the cc side.
 //
-// Typical usage is to deliver ready-to-be-displayed video frames to
-// UpdateCurrentFrame() so that VideoFrameCompositor can take care of tracking
-// changes in video frames and firing callbacks as needed.
+// This class is responsible for requesting new frames from the video renderer
+// in response to requests from the VFP::Client. It is also responsible for
+// requesting new frames when the VFP::Client stops doing so in response to
+// visibility changes of the output layer.
+//
+// This class is responsible for detected frames dropped by the compositor after

[xhwang, 2015/04/13 20:50:29]

s/detected/detecting, hmm actually "signaling"?

[DaleCurtis, 2015/04/13 23:15:06]

Done.

+// rendering; this is done by ensuring each GetCurrentFrame() is followed by a
+// PutCurrentFrame() before the next UpdateCurrentFrame() call.

[xhwang, 2015/04/13 20:50:29]

By doing so, we are signaling frame-not-dropped... Needs a bit polish here.

[DaleCurtis, 2015/04/13 23:15:06]

Done.

+//
+// VideoRenderSink::RenderCallback implementations must call Start() and Stop()
+// once new frames are expected or are no longer expected to be ready; this data
+// is relayed to the compositor to avoid extraneous callbacks.
 //
 // VideoFrameCompositor must live on the same thread as the compositor.
 class MEDIA_EXPORT VideoFrameCompositor
-    : NON_EXPORTED_BASE(public cc::VideoFrameProvider) {
+    : public VideoRendererSink,
+      NON_EXPORTED_BASE(public cc::VideoFrameProvider) {
  public:
+  // |compositor_task_runner| is the task runner on which this class will live.

[xhwang, 2015/04/13 20:50:29]

Clarify what this means. There are still methods called on the media thread.
Also, |this| can be constructed on another thread as well.

[DaleCurtis, 2015/04/13 23:15:06]

Clarified which methods are called where.

+  //
   // |natural_size_changed_cb| is run with the new natural size of the video
   // frame whenever a change in natural size is detected. It is not called the
   // first time UpdateCurrentFrame() is called. Run on the same thread as the
@@ -34,31 +51,56 @@ class MEDIA_EXPORT VideoFrameCompositor
   // called the first time UpdateCurrentFrame() is called. Run on the same
   // thread as the caller of UpdateCurrentFrame().
   //
-  // TODO(scherkus): Investigate the inconsistency between the callbacks with
+  // TODO(dalecurtis): Investigate the inconsistency between the callbacks with
   // respect to why we don't call |natural_size_changed_cb| on the first frame.
   // I suspect it was for historical reasons that no longer make sense.
   VideoFrameCompositor(
+      const scoped_refptr<base::SingleThreadTaskRunner>& compositor_task_runner,
       const base::Callback<void(gfx::Size)>& natural_size_changed_cb,
       const base::Callback<void(bool)>& opacity_changed_cb);
+
+  // Destruction must happen on the compositor thread; Stop() must have been
+  // called before destruction starts.
   ~VideoFrameCompositor() override;
 
+  // Returns |current_frame_| if it was refreshed in the last 250ms; otherwise,
+  // if |callback_| is available, requests a new frame and returns that one.
+  scoped_refptr<VideoFrame> GetCurrentFrameAndUpdateIfStale();

[xhwang, 2015/04/13 20:50:29]

Add a comment about why we need this? e.g. canvas, which can help justify the
choice of 250ms.

Also, try not to hardcode the 250ms here?

[DaleCurtis, 2015/04/13 23:15:06]

Done.

+
   // cc::VideoFrameProvider implementation.
   void SetVideoFrameProviderClient(
       cc::VideoFrameProvider::Client* client) override;
+  bool UpdateCurrentFrame(base::TimeTicks deadline_min,
+                          base::TimeTicks deadline_max) override;
   scoped_refptr<VideoFrame> GetCurrentFrame() override;
-  void PutCurrentFrame(const scoped_refptr<VideoFrame>& frame) override;
+  void PutCurrentFrame() override;
 
-  // Updates the current frame and notifies the compositor.
-  void UpdateCurrentFrame(const scoped_refptr<VideoFrame>& frame);
+  // VideoRendererSink implementation.
+  void Start(RenderCallback* callback) override;
+  void Stop() override;
+  void PaintFrameUsingOldRenderingPath(
+      const scoped_refptr<VideoFrame>& frame) override;
 
  private:
+  // Called on the compositor thread to start or stop rendering if rendering was
+  // previously started or stopped before we had a |callback_|.
+  void OnRendererStateUpdate();
+
+  scoped_refptr<base::SingleThreadTaskRunner> compositor_task_runner_;
+
+  // These callbacks are executed on the compositor thread.
   base::Callback<void(gfx::Size)> natural_size_changed_cb_;
   base::Callback<void(bool)> opacity_changed_cb_;
 
+  // These values are only set and read on the compositor thread.
   cc::VideoFrameProvider::Client* client_;
-
   scoped_refptr<VideoFrame> current_frame_;
 
+  // These values are updated and read from the media and compositor threads.
+  base::Lock lock_;
+  bool rendering_;
+  VideoRendererSink::RenderCallback* callback_;
+
   DISALLOW_COPY_AND_ASSIGN(VideoFrameCompositor);
 };