update method
Updates the internal state of this time object.
Implementation
Time update() {
if ( _useFixedDelta == true ) {
_delta = _fixedDelta;
}
else {
_previousTime = _currentTime;
_currentTime = _now();
_delta = _currentTime - _previousTime;
}
_delta *= _timescale;
_elapsed += _delta; // _elapsed is the accumulation of all previous deltas
return this;
}