cc/CCFrameRateCounter.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 CCFrameRateCounter_h
   6 #define CCFrameRateCounter_h
   7
   8 #if USE(ACCELERATED_COMPOSITING)
   9
  10 #include <wtf/Noncopyable.h>
  11 #include <wtf/PassOwnPtr.h>
  12
  13 namespace WebCore {
  14
  15 // This class maintains a history of timestamps, and provides functionality to
  16 // intelligently compute average frames per second (and standard deviation).
  17 class CCFrameRateCounter {
  18     WTF_MAKE_NONCOPYABLE(CCFrameRateCounter);
  19 public:
  20     static PassOwnPtr<CCFrameRateCounter> create()
  21     {
  22         return adoptPtr(new CCFrameRateCounter());
  23     }
  24
  25     void markBeginningOfFrame(double timestamp);
  26     void markEndOfFrame();
  27     int currentFrameNumber() const { return m_currentFrameNumber; }
  28     void getAverageFPSAndStandardDeviation(double& averageFPS, double& standardDeviation) const;
  29     int timeStampHistorySize() const { return kTimeStampHistorySize; }
  30
  31     // n = 0 returns the oldest frame retained in the history,
  32     // while n = timeStampHistorySize() - 1 returns the timestamp most recent frame.
  33     double timeStampOfRecentFrame(int /* n */);
  34
  35     // This is a heuristic that can be used to ignore frames in a reasonable way. Returns
  36     // true if the given frame interval is too fast or too slow, based on constant thresholds.
  37     bool isBadFrameInterval(double intervalBetweenConsecutiveFrames) const;
  38
  39     int droppedFrameCount() const { return m_droppedFrameCount; }
  40
  41 private:
  42     CCFrameRateCounter();
  43
  44     double frameInterval(int frameNumber) const;
  45     int frameIndex(int frameNumber) const;
  46     bool isBadFrame(int frameNumber) const;
  47
  48     // Two thresholds (measured in seconds) that describe what is considered to be a "no-op frame" that should not be counted.
  49     // - if the frame is too fast, then given our compositor implementation, the frame probably was a no-op and did not draw.
  50     // - if the frame is too slow, then there is probably not animating content, so we should not pollute the average.
  51     static const double kFrameTooFast;
  52     static const double kFrameTooSlow;
  53
  54     // If a frame takes longer than this threshold (measured in seconds) then we
  55     // (naively) assume that it missed a screen refresh; that is, we dropped a frame.
  56     // FIXME: Determine this threshold based on monitor refresh rate, crbug.com/138642.
  57     static const double kDroppedFrameTime;
  58
  59     static const int kTimeStampHistorySize = 120;
  60
  61     int m_currentFrameNumber;
  62     double m_timeStampHistory[kTimeStampHistorySize];
  63
  64     int m_droppedFrameCount;
  65 };
  66
  67 } // namespace WebCore
  68
  69 #endif // USE(ACCELERATED_COMPOSITING)
  70
  71 #endif