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1 /*
2  *  Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
3  *
4  *  Use of this source code is governed by a BSD-style license
5  *  that can be found in the LICENSE file in the root of the source
6  *  tree. An additional intellectual property rights grant can be found
7  *  in the file PATENTS.  All contributing project authors may
8  *  be found in the AUTHORS file in the root of the source tree.
9  */
10 
11 #ifndef WEBRTC_MODULES_DESKTOP_CAPTURE_SCREEN_CAPTURE_FRAME_QUEUE_H_
12 #define WEBRTC_MODULES_DESKTOP_CAPTURE_SCREEN_CAPTURE_FRAME_QUEUE_H_
13 
14 #include "webrtc/base/scoped_ptr.h"
15 #include "webrtc/modules/desktop_capture/shared_desktop_frame.h"
16 #include "webrtc/typedefs.h"
17 
18 namespace webrtc {
19 class DesktopFrame;
20 }  // namespace webrtc
21 
22 namespace webrtc {
23 
24 // Represents a queue of reusable video frames. Provides access to the 'current'
25 // frame - the frame that the caller is working with at the moment, and to the
26 // 'previous' frame - the predecessor of the current frame swapped by
27 // MoveToNextFrame() call, if any.
28 //
29 // The caller is expected to (re)allocate frames if current_frame() returns
30 // NULL. The caller can mark all frames in the queue for reallocation (when,
31 // say, frame dimensions change). The queue records which frames need updating
32 // which the caller can query.
33 //
34 // Frame consumer is expected to never hold more than kQueueLength frames
35 // created by this function and it should release the earliest one before trying
36 // to capture a new frame (i.e. before MoveToNextFrame() is called).
37 class ScreenCaptureFrameQueue {
38  public:
39   ScreenCaptureFrameQueue();
40   ~ScreenCaptureFrameQueue();
41 
42   // Moves to the next frame in the queue, moving the 'current' frame to become
43   // the 'previous' one.
44   void MoveToNextFrame();
45 
46   // Replaces the current frame with a new one allocated by the caller. The
47   // existing frame (if any) is destroyed. Takes ownership of |frame|.
48   void ReplaceCurrentFrame(DesktopFrame* frame);
49 
50   // Marks all frames obsolete and resets the previous frame pointer. No
51   // frames are freed though as the caller can still access them.
52   void Reset();
53 
current_frame()54   SharedDesktopFrame* current_frame() const {
55     return frames_[current_].get();
56   }
57 
previous_frame()58   SharedDesktopFrame* previous_frame() const {
59     return frames_[(current_ + kQueueLength - 1) % kQueueLength].get();
60   }
61 
62  private:
63   // Index of the current frame.
64   int current_;
65 
66   static const int kQueueLength = 2;
67   rtc::scoped_ptr<SharedDesktopFrame> frames_[kQueueLength];
68 
69   RTC_DISALLOW_COPY_AND_ASSIGN(ScreenCaptureFrameQueue);
70 };
71 
72 }  // namespace webrtc
73 
74 #endif  // WEBRTC_MODULES_DESKTOP_CAPTURE_SCREEN_CAPTURE_FRAME_QUEUE_H_
75