阅读下面的代码片段，说明它的用途。float m_fireRate = 0f;float m_fireDeltaTime = 0.2f;void Update () {m_fireRate -= Time.deltaTime;if(m_fireRate < 0 ) {m_fireRate = m_fireDeltaTime;if(Input.GetButton("Fire1")) {//生成一个rocket_prefab的预设Instantiate(rocket_prefab, m_transform.position , m_transform.rotation);}}}