cc/frame_rate_counter.h

   1 // Copyright 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef CC_FRAME_RATE_COUNTER_H_
   6 #define CC_FRAME_RATE_COUNTER_H_
   7
   8 #include "base/basictypes.h"
   9 #include "base/memory/scoped_ptr.h"
  10 #include "base/time.h"
  11
  12 namespace cc {
  13
  14 // This class maintains a history of timestamps, and provides functionality to
  15 // intelligently compute average frames per second.
  16 class FrameRateCounter {
  17 public:
  18     static scoped_ptr<FrameRateCounter> create(bool hasImplThread);
  19
  20     void markBeginningOfFrame(base::TimeTicks timestamp);
  21     void markEndOfFrame();
  22     int currentFrameNumber() const { return m_currentFrameNumber; }
  23     double getAverageFPS() const;
  24     int timeStampHistorySize() const { return kTimeStampHistorySize; }
  25
  26     // n = 0 returns the oldest frame retained in the history,
  27     // while n = timeStampHistorySize() - 1 returns the timestamp most recent frame.
  28     // FIXME: Returns most recent timestamp for n = 0 when called between markBeginningOfFrame and markEndOfFrame calls.
  29     base::TimeTicks timeStampOfRecentFrame(int n) const;
  30
  31     // This is a heuristic that can be used to ignore frames in a reasonable way. Returns
  32     // true if the given frame interval is too fast or too slow, based on constant thresholds.
  33     bool isBadFrameInterval(base::TimeDelta intervalBetweenConsecutiveFrames) const;
  34
  35     int droppedFrameCount() const { return m_droppedFrameCount; }
  36
  37 private:
  38     explicit FrameRateCounter(bool hasImplThread);
  39
  40     base::TimeDelta frameInterval(int frameNumber) const;
  41     int frameIndex(int frameNumber) const;
  42     bool isBadFrame(int frameNumber) const;
  43
  44     // Two thresholds (measured in seconds) that describe what is considered to be a "no-op frame" that should not be counted.
  45     // - if the frame is too fast, then given our compositor implementation, the frame probably was a no-op and did not draw.
  46     // - if the frame is too slow, then there is probably not animating content, so we should not pollute the average.
  47     static const double kFrameTooFast;
  48     static const double kFrameTooSlow;
  49
  50     // If a frame takes longer than this threshold (measured in seconds) then we
  51     // (naively) assume that it missed a screen refresh; that is, we dropped a frame.
  52     // FIXME: Determine this threshold based on monitor refresh rate, crbug.com/138642.
  53     static const double kDroppedFrameTime;
  54
  55     static const int kTimeStampHistorySize = 170;
  56
  57     bool m_hasImplThread;
  58
  59     int m_currentFrameNumber;
  60     base::TimeTicks m_timeStampHistory[kTimeStampHistorySize];
  61
  62     int m_droppedFrameCount;
  63
  64     DISALLOW_COPY_AND_ASSIGN(FrameRateCounter);
  65 };
  66
  67 }  // namespace cc
  68
  69 #endif  // CC_FRAME_RATE_COUNTER_H_