text: /*
   *  Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
   *
   *  Use of this source code is governed by a BSD-style license
   *  that can be found in the LICENSE file in the root of the source
   *  tree. An additional intellectual property rights grant can be found
   *  in the file PATENTS.  All contributing project authors may
   *  be found in the AUTHORS file in the root of the source tree.
   */
  
  #ifndef WEBRTC_MODULES_DESKTOP_CAPTURE_SCREEN_CAPTURE_FRAME_QUEUE_H_
  #define WEBRTC_MODULES_DESKTOP_CAPTURE_SCREEN_CAPTURE_FRAME_QUEUE_H_
  
  #include <memory>
  
  #include "webrtc/base/constructormagic.h"
  // TODO(zijiehe): These headers are not used in this file, but to avoid build
  // break in remoting/host. We should add headers in each individual files.
  #include "webrtc/modules/desktop_capture/desktop_frame.h"  // Remove
  #include "webrtc/modules/desktop_capture/shared_desktop_frame.h"  // Remove
  
  
  namespace webrtc {
  
  // Represents a queue of reusable video frames. Provides access to the 'current'
  // frame - the frame that the caller is working with at the moment, and to the
  // 'previous' frame - the predecessor of the current frame swapped by
  // MoveToNextFrame() call, if any.
  //
  // The caller is expected to (re)allocate frames if current_frame() returns
  // NULL. The caller can mark all frames in the queue for reallocation (when,
  // say, frame dimensions change). The queue records which frames need updating
  // which the caller can query.
  //
  // Frame consumer is expected to never hold more than kQueueLength frames
  // created by this function and it should release the earliest one before trying
  // to capture a new frame (i.e. before MoveToNextFrame() is called).
  template <typename FrameType>
  class ScreenCaptureFrameQueue {
   public:
    ScreenCaptureFrameQueue() : current_(0) {}
    ~ScreenCaptureFrameQueue() = default;
  
    // Moves to the next frame in the queue, moving the 'current' frame to become
    // the 'previous' one.
    void MoveToNextFrame() {
      current_ = (current_ + 1) % kQueueLength;
    }
  
    // Replaces the current frame with a new one allocated by the caller. The
    // existing frame (if any) is destroyed. Takes ownership of |frame|.
    void ReplaceCurrentFrame(std::unique_ptr<FrameType> frame) {
      frames_[current_] = std::move(frame);
    }
  
    // Marks all frames obsolete and resets the previous frame pointer. No
    // frames are freed though as the caller can still access them.
    void Reset() {
      for (int i = 0; i < kQueueLength; i++) {
        frames_[i].reset();
      }
      current_ = 0;
    }
  
    FrameType* current_frame() const {
      return frames_[current_].get();
    }
  
    FrameType* previous_frame() const {
      return frames_[(current_ + kQueueLength - 1) % kQueueLength].get();
    }
  
   private:
    // Index of the current frame.
    int current_;
  
    static const int kQueueLength = 2;
    std::unique_ptr<FrameType> frames_[kQueueLength];
  
    RTC_DISALLOW_COPY_AND_ASSIGN(ScreenCaptureFrameQueue);
  };
  
  }  // namespace webrtc
  
  #endif  // WEBRTC_MODULES_DESKTOP_CAPTURE_SCREEN_CAPTURE_FRAME_QUEUE_H_
  