code: public void update(int delta) {
  		emitter.updateParticle(this, delta);
  		life -= delta;
  		
  		if (life > 0) {
  			x += delta * velx;
  			y += delta * vely;
  		} else {
  			engine.release(this);
  		}
  	}
docs: Update the state of this particle
  
  @param delta
  The time since the last update