elapseTime method

void elapseTime(double seconds)

Advance the simulation by seconds.

Implementation

void elapseTime(double seconds) {
  if (isDone) return;

  double secondsRemaining = seconds;
  const maxStepSize = 1.0 / 60.0;

  while (secondsRemaining > 0.0) {
    final stepSize = secondsRemaining > maxStepSize
        ? maxStepSize
        : secondsRemaining;

    // THE KEY FEATURE: acceleration ramp.
    // Grows from 0→1 at rate 6.0/s. At 60fps that's 0→1 in ~10 frames (167ms).
    // This is why Fuchsia springs start gentle instead of yanking.
    _accelerationMultiplier = math.min(
      1.0,
      _accelerationMultiplier + stepSize * 6.0,
    );

    if (_evaluateRK(stepSize)) {
      _curT = 1.0;
      _value = _target;
      _velocity = 0.0;
      _isDone = true;
      _accelerationMultiplier = 0.0;
      return;
    }
    secondsRemaining -= maxStepSize;
  }
  _value = _startValue + _curT * _delta;
}