// 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 CC_FRAME_RATE_COUNTER_H_
#define CC_FRAME_RATE_COUNTER_H_

#include "base/basictypes.h"
#include "base/memory/scoped_ptr.h"
#include "base/time.h"
#include "cc/ring_buffer.h"

namespace cc {

// This class maintains a history of timestamps, and provides functionality to
// intelligently compute average frames per second.
class FrameRateCounter {
public:
    static scoped_ptr<FrameRateCounter> create(bool hasImplThread);

    int currentFrameNumber() const { return m_ringBuffer.CurrentIndex(); }
    int droppedFrameCount() const { return m_droppedFrameCount; }
    size_t timeStampHistorySize() const { return m_ringBuffer.BufferSize(); }

    void saveTimeStamp(base::TimeTicks timestamp);

    // n = 0 returns the oldest frame interval retained in the history,
    // while n = timeStampHistorySize() - 1 returns the most recent frame interval.
    base::TimeDelta recentFrameInterval(size_t n) const;

    // 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;

    void getMinAndMaxFPS(double& minFPS, double& maxFPS) const;
    double getAverageFPS() const;

    typedef RingBuffer<base::TimeTicks, 136> RingBufferType;
    RingBufferType::Iterator begin() const { return m_ringBuffer.Begin(); }
    RingBufferType::Iterator end() const { return m_ringBuffer.End(); }

private:
    explicit FrameRateCounter(bool hasImplThread);

    // 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;

    RingBufferType m_ringBuffer;

    bool m_hasImplThread;
    int m_droppedFrameCount;

    DISALLOW_COPY_AND_ASSIGN(FrameRateCounter);
};

}  // namespace cc

#endif  // CC_FRAME_RATE_COUNTER_H_