third_party/WebKit/Source/core/animation/AnimationClock.cpp

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#include "core/animation/AnimationClock.h"

#include "wtf/CurrentTime.h"
#include <math.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.
const double approximateFrameTime = 1 / 60.0;
}

namespace blink {

unsigned AnimationClock::s_currentlyRunningTask = 0;

void AnimationClock::updateTime(double time) {
  if (time > m_time)
    m_time = time;
  m_taskForWhichTimeWasCalculated = s_currentlyRunningTask;
}

double AnimationClock::currentTime() {
  if (m_taskForWhichTimeWasCalculated != s_currentlyRunningTask) {
    const double currentTime = m_monotonicallyIncreasingTime();
    if (m_time < currentTime) {
      // Advance to the first estimated frame after the current time.
      const double frameShift =
          fmod(currentTime - m_time, approximateFrameTime);
      const double newTime = currentTime + (approximateFrameTime - frameShift);
      DCHECK_GE(newTime, currentTime);
      DCHECK_LE(newTime, currentTime + approximateFrameTime);
      updateTime(newTime);
    } else {
      m_taskForWhichTimeWasCalculated = s_currentlyRunningTask;
    }
  }
  return m_time;
}

void AnimationClock::resetTimeForTesting(double time) {
  m_time = time;
  m_taskForWhichTimeWasCalculated = 0;
  s_currentlyRunningTask = 0;
}

}  // namespace blink