public Emitter centerEmitter() {
   Emitter emitter = GameScene.emitter();
   emitter.pos(center());
   return emitter;
 }
 public Emitter bottomEmitter() {
   Emitter emitter = GameScene.emitter();
   emitter.pos(x, y + height, width, 0);
   return emitter;
 }
 public Emitter emitter() {
   Emitter emitter = GameScene.emitter();
   emitter.pos(this);
   return emitter;
 }