public void RemoveBallSpawner(IBallSpawner spawner)
 {
     spawner.spawnBallAtPositionWithScale -= SpawnBallAtPositionWithScale;
 }
 public void AddBallSpawner(IBallSpawner spawner)
 {
     spawner.spawnBallAtPositionWithScale += SpawnBallAtPositionWithScale;
 }