update method

@override void update(ParticleStorage storage, double dt)

Advances every live particle by dt seconds.

Implementation

@override
void update(ParticleStorage storage, double dt) {
  final count = frameCount.toDouble();
  final fps = framesPerSecond;
  final n = storage.aliveCount;
  for (var i = 0; i < n; i++) {
    var frame = 0.0;
    if (fps == null) {
      final life = storage.lifetime[i];
      final nAge = life > 0.0 ? storage.age[i] / life : 0.0;
      // Clamp shy of the end so the last cell holds instead of wrapping.
      frame = nAge * count;
      if (frame > count - 1.0) frame = count - 1.0;
    } else {
      frame = storage.age[i] * fps;
    }
    if (randomStartFrame) {
      frame += storage.randomFor(i, _saltFlipbookStart) * count;
    }
    storage.frame[i] = frame % count;
  }
}