third_party/blink/renderer/core/animation/animation_clock.cc

/*
 * Copyright (c) 2014, Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
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 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
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 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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#include "third_party/blink/renderer/core/animation/animation_clock.h"

#include <math.h>
#include "third_party/blink/renderer/platform/wtf/time.h"

namespace {

// FIXME: This is an approximation of time between frames, used when
// ticking the animation clock outside of animation frame callbacks.
// Ideally this would be generated by the compositor.
constexpr base::TimeDelta kApproximateFrameTime =
    base::TimeDelta::FromSecondsD(1 / 60.0);
}

namespace blink {

unsigned AnimationClock::currently_running_task_ = 0;

void AnimationClock::UpdateTime(base::TimeTicks time) {
  if (time > time_)
    time_ = time;
  task_for_which_time_was_calculated_ = currently_running_task_;
}

double AnimationClock::CurrentTime() {
  if (monotonically_increasing_time_ &&
      task_for_which_time_was_calculated_ != currently_running_task_) {
    const base::TimeTicks current_time = monotonically_increasing_time_();
    if (time_ < current_time) {
      // Advance to the first estimated frame after the current time.
      const base::TimeDelta frame_shift =
          (current_time - time_) % kApproximateFrameTime;
      const base::TimeTicks new_time =
          current_time + kApproximateFrameTime - frame_shift;
      DCHECK_GE(new_time, current_time);
      DCHECK_LE(new_time, current_time + kApproximateFrameTime);
      UpdateTime(new_time);
    } else {
      task_for_which_time_was_calculated_ = currently_running_task_;
    }
  }
  return time_.since_origin().InSecondsF();
}

void AnimationClock::ResetTimeForTesting(base::TimeTicks time) {
  time_ = time;
  task_for_which_time_was_calculated_ = 0;
  currently_running_task_ = 0;
}

}  // namespace blink