move method
Implementation
void move(EffectBirthdayOneParams params) {
params.y = params.y! + params.speed!;
double offsetX = sin(params.y! / (300 + 50 * params.alpha!)) *
(1 + 0.5 * params.alpha!) ;
params.x = params.x! + offsetX;
if (params.y! > params.height!) {
params.y = -params.height! + Random().nextInt(params.height!.toInt());
params.reset();
}
}