media/blink/video_frame_compositor.h

// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef MEDIA_BLINK_VIDEO_FRAME_COMPOSITOR_H_
#define MEDIA_BLINK_VIDEO_FRAME_COMPOSITOR_H_

#include <utility>

#include "base/callback.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/single_thread_task_runner.h"
#include "base/synchronization/lock.h"
#include "base/time/tick_clock.h"
#include "base/timer/timer.h"
#include "cc/layers/video_frame_provider.h"
#include "media/base/video_renderer_sink.h"
#include "media/blink/media_blink_export.h"
#include "ui/gfx/geometry/size.h"

namespace media {
class VideoFrame;

// VideoFrameCompositor acts as a bridge between the media and cc layers 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.
//
// This class is responsible for requesting new frames from a video renderer in
// response to requests from the VFP::Client. Since the VFP::Client may stop
// issuing requests in response to visibility changes it is also responsible for
// ensuring the "freshness" of the current frame for programmatic frame
// requests; e.g., Canvas.drawImage() requests
//
// This class is also responsible for detecting frames dropped by the compositor
// after rendering and signaling that information to a RenderCallback. It
// detects frames not dropped by verifying each GetCurrentFrame() is followed
// by a PutCurrentFrame() before the next UpdateCurrentFrame() call.
//
// 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 is also responsible for pumping UpdateCurrentFrame()
// callbacks in the background when |client_| has decided to suspend them.
//
// VideoFrameCompositor must live on the same thread as the compositor, though
// it may be constructed on any thread.
class MEDIA_BLINK_EXPORT VideoFrameCompositor
    : public VideoRendererSink,
      NON_EXPORTED_BASE(public cc::VideoFrameProvider) {
 public:
  // |compositor_task_runner| is the task runner on which this class will live,
  // though it may be constructed on any thread.
  explicit VideoFrameCompositor(
      const scoped_refptr<base::SingleThreadTaskRunner>&
          compositor_task_runner);

  // Destruction must happen on the compositor thread; Stop() must have been
  // called before destruction starts.
  ~VideoFrameCompositor() override;

  // cc::VideoFrameProvider implementation. These methods must be called on the
  // |compositor_task_runner_|.
  void SetVideoFrameProviderClient(
      cc::VideoFrameProvider::Client* client) override;
  bool UpdateCurrentFrame(base::TimeTicks deadline_min,
                          base::TimeTicks deadline_max) override;
  bool HasCurrentFrame() override;
  scoped_refptr<VideoFrame> GetCurrentFrame() override;
  void PutCurrentFrame() override;

  // VideoRendererSink implementation. These methods must be called from the
  // same thread (typically the media thread).
  void Start(RenderCallback* callback) override;
  void Stop() override;
  void PaintSingleFrame(const scoped_refptr<VideoFrame>& frame) override;

  // Returns |current_frame_| if |client_| is set.  If no |client_| is set,
  // |is_background_rendering_| is true, and |callback_| is set, it requests a
  // new frame from |callback_|, using the elapsed time between calls to this
  // function as the render interval; defaulting to 16.6ms if no prior calls
  // have been made.  A cap of 250Hz (4ms) is in place to prevent clients from
  // accidentally (or intentionally) spamming the rendering pipeline.
  //
  // This method is primarily to facilitate canvas and WebGL based applications
  // where the <video> tag is invisible (possibly not even in the DOM) and thus
  // does not receive a |client_|.  In this case, frame acquisition is driven by
  // the frequency of canvas or WebGL paints requested via JavaScript.
  scoped_refptr<VideoFrame> GetCurrentFrameAndUpdateIfStale();

  // Returns the timestamp of the current (possibly stale) frame, or
  // base::TimeDelta() if there is no current frame. This method may be called
  // from the media thread as long as the VFC is stopped. (Assuming that
  // PaintSingleFrame() is not also called while stopped.)
  base::TimeDelta GetCurrentFrameTimestamp() const;

  void set_tick_clock_for_testing(std::unique_ptr<base::TickClock> tick_clock) {
    tick_clock_ = std::move(tick_clock);
  }

  void clear_current_frame_for_testing() { current_frame_ = nullptr; }

  // Enables or disables background rendering. If |enabled|, |timeout| is the
  // amount of time to wait after the last Render() call before starting the
  // background rendering mode.  Note, this can not disable the background
  // rendering call issues when a sink is started.
  void set_background_rendering_for_testing(bool enabled) {
    background_rendering_enabled_ = enabled;
  }

 private:
  // Called on the compositor thread in response to Start() or Stop() calls;
  // must be used to change |rendering_| state.
  void OnRendererStateUpdate(bool new_state);

  // Handles setting of |current_frame_|.
  bool ProcessNewFrame(const scoped_refptr<VideoFrame>& frame);

  // Called by |background_rendering_timer_| when enough time elapses where we
  // haven't seen a Render() call.
  void BackgroundRender();

  // If |callback_| is available, calls Render() with the provided properties.
  // Updates |is_background_rendering_|, |last_interval_|, and resets
  // |background_rendering_timer_|. Returns true if there's a new frame
  // available via GetCurrentFrame().
  bool CallRender(base::TimeTicks deadline_min,
                  base::TimeTicks deadline_max,
                  bool background_rendering);

  scoped_refptr<base::SingleThreadTaskRunner> compositor_task_runner_;
  std::unique_ptr<base::TickClock> tick_clock_;

  // Allows tests to disable the background rendering task.
  bool background_rendering_enabled_;

  // Manages UpdateCurrentFrame() callbacks if |client_| has stopped sending
  // them for various reasons.  Runs on |compositor_task_runner_| and is reset
  // after each successful UpdateCurrentFrame() call.
  base::Timer background_rendering_timer_;

  // These values are only set and read on the compositor thread.
  cc::VideoFrameProvider::Client* client_;
  bool rendering_;
  bool rendered_last_frame_;
  bool is_background_rendering_;
  bool new_background_frame_;
  base::TimeDelta last_interval_;
  base::TimeTicks last_background_render_;

  // These values are set on the compositor thread, but also read on the media
  // thread when the VFC is stopped.
  scoped_refptr<VideoFrame> current_frame_;

  // These values are updated and read from the media and compositor threads.
  base::Lock callback_lock_;
  VideoRendererSink::RenderCallback* callback_;

  DISALLOW_COPY_AND_ASSIGN(VideoFrameCompositor);
};

}  // namespace media

#endif  // MEDIA_BLINK_VIDEO_FRAME_COMPOSITOR_H_