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// Copyright (c) 2015 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 MEDIA_CAPTURE_SMOOTH_EVENT_SAMPLER_H_
#define MEDIA_CAPTURE_SMOOTH_EVENT_SAMPLER_H_
#include "base/time/time.h"
#include "media/base/media_export.h"
namespace media {
// Filters a sequence of events to achieve a target frequency.
class MEDIA_EXPORT SmoothEventSampler {
public:
enum {
// The maximum amount of time that can elapse before considering unchanged
// content as dirty for the purposes of timer-based overdue sampling. This
// is the same value found in cc::FrameRateCounter.
OVERDUE_DIRTY_THRESHOLD_MILLIS = 250 // 4 FPS
};
SmoothEventSampler(base::TimeDelta min_capture_period,
int redundant_capture_goal);
// Get/Set minimum capture period. When setting a new value, the state of the
// sampler is retained so that sampling will continue smoothly.
base::TimeDelta min_capture_period() const { return min_capture_period_; }
void SetMinCapturePeriod(base::TimeDelta p);
// Add a new event to the event history, and consider whether it ought to be
// sampled. The event is not recorded as a sample until RecordSample() is
// called.
void ConsiderPresentationEvent(base::TimeTicks event_time);
// Returns true if the last event considered should be sampled.
bool ShouldSample() const;
// Operates on the last event added by ConsiderPresentationEvent(), marking
// it as sampled. After this point we are current in the stream of events, as
// we have sampled the most recent event.
void RecordSample();
// Returns true if, at time |event_time|, sampling should occur because too
// much time will have passed relative to the last event and/or sample.
bool IsOverdueForSamplingAt(base::TimeTicks event_time) const;
// Returns true if ConsiderPresentationEvent() has been called since the last
// call to RecordSample().
bool HasUnrecordedEvent() const;
private:
base::TimeDelta min_capture_period_;
const int redundant_capture_goal_;
base::TimeDelta token_bucket_capacity_;
base::TimeTicks current_event_;
base::TimeTicks last_sample_;
int overdue_sample_count_;
base::TimeDelta token_bucket_;
DISALLOW_COPY_AND_ASSIGN(SmoothEventSampler);
};
} // namespace media
#endif // MEDIA_CAPTURE_SMOOTH_EVENT_SAMPLER_H_
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