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// Copyright 2012 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 CCFrameRateCounter_h
#define CCFrameRateCounter_h
#if USE(ACCELERATED_COMPOSITING)
#include "base/basictypes.h"
#include "base/memory/scoped_ptr.h"
#include "base/time.h"
namespace cc {
// This class maintains a history of timestamps, and provides functionality to
// intelligently compute average frames per second (and standard deviation).
class CCFrameRateCounter {
public:
static scoped_ptr<CCFrameRateCounter> create();
void markBeginningOfFrame(base::TimeTicks timestamp);
void markEndOfFrame();
int currentFrameNumber() const { return m_currentFrameNumber; }
void getAverageFPSAndStandardDeviation(double& averageFPS, double& standardDeviation) const;
int timeStampHistorySize() const { return kTimeStampHistorySize; }
// n = 0 returns the oldest frame retained in the history,
// while n = timeStampHistorySize() - 1 returns the timestamp most recent frame.
base::TimeTicks timeStampOfRecentFrame(int n);
// This is a heuristic that can be used to ignore frames in a reasonable way. Returns
// true if the given frame interval is too fast or too slow, based on constant thresholds.
bool isBadFrameInterval(base::TimeDelta intervalBetweenConsecutiveFrames) const;
int droppedFrameCount() const { return m_droppedFrameCount; }
private:
CCFrameRateCounter();
base::TimeDelta frameInterval(int frameNumber) const;
int frameIndex(int frameNumber) const;
bool isBadFrame(int frameNumber) const;
// Two thresholds (measured in seconds) that describe what is considered to be a "no-op frame" that should not be counted.
// - if the frame is too fast, then given our compositor implementation, the frame probably was a no-op and did not draw.
// - if the frame is too slow, then there is probably not animating content, so we should not pollute the average.
static const double kFrameTooFast;
static const double kFrameTooSlow;
// If a frame takes longer than this threshold (measured in seconds) then we
// (naively) assume that it missed a screen refresh; that is, we dropped a frame.
// FIXME: Determine this threshold based on monitor refresh rate, crbug.com/138642.
static const double kDroppedFrameTime;
static const int kTimeStampHistorySize = 120;
int m_currentFrameNumber;
base::TimeTicks m_timeStampHistory[kTimeStampHistorySize];
int m_droppedFrameCount;
DISALLOW_COPY_AND_ASSIGN(CCFrameRateCounter);
};
} // namespace cc
#endif // USE(ACCELERATED_COMPOSITING)
#endif
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