1. override
bool advanceTime(num time)

This method is called by the Juggler with the time past since the last call.

Returns true as long as this Animatable is not completed; false if it is completed.

Source 

@override
bool advanceTime(num time) {

  if (_currentTime < _totalTime || _started == false) {
    _currentTime = _currentTime + time;

    if (_currentTime > _totalTime) _currentTime = _totalTime;

    if (_currentTime >= 0.0) {
      if (_started == false) {
        _started = true;
        if (_onStart != null) _onStart();
      }

      num ratio = _currentTime / _totalTime;
      num transition = _transition(ratio);

      _currentValue = _startValue + transition * (_targetValue - _startValue);

      if (_onUpdate != null) _onUpdate(_roundToInt ? _currentValue.round() : _currentValue);
      if (_onComplete != null && _currentTime == _totalTime) _onComplete();
    }
  }

  return _currentTime < _totalTime;
}