/// <summary>
/// 掛載到發射器上即可
/// </summary>
public class Rotate : MonoBehaviour
{
 public GameObject prefab; //發射物
 public float speed;   //發射物速度
 public bool 拋射 = false; //拋射：仰角 > 45°，否：仰角 < 45°
 Ray RayMouse;
 Vector3 direction;
 Quaternion rotation;
 
 void Update()
 {
  if (Input.GetMouseButtonDown(0))
  {
   GameObject go = Instantiate(prefab, transform.position, transform.rotation);
   go.AddComponent<Rigidbody>().velocity = go.transform.forward * speed;
  }

  RaycastHit hit;
  RayMouse = Camera.main.ScreenPointToRay(Input.mousePosition);
  if (Physics.Raycast(RayMouse.origin, RayMouse.direction, out hit, Mathf.Infinity))
  {
   RotateToMouseDirection(gameObject, hit.point);
  }
 }

 /// <summary>
 /// 執行整體旋轉
 /// </summary>
 /// <param name="obj">旋轉的物體（自身）</param>
 /// <param name="destination">目標點（鼠標指向）</param>
 void RotateToMouseDirection(GameObject obj, Vector3 destination)
 {
  direction = destination - obj.transform.position;
  rotation = Quaternion.LookRotation(direction);

  Vector3 finalAngle = rotation.eulerAngles;
  float targetAng = Angle(destination);
  finalAngle = new Vector3(-targetAng, finalAngle.y, finalAngle.z);//注意正負

  obj.transform.localRotation = Quaternion.Euler(finalAngle);
 }

 /// <summary>
 /// 自動計算x歐拉角，即仰角
 /// </summary>
 /// <param name="target">目標點坐標</param>
 /// <returns></returns>
 float Angle(Vector3 target)
 {
  float angleX;
  float distX = Vector2.Distance(new Vector2(target.x, target.z), new Vector2(transform.position.x, transform.position.z));
  float distY = target.y - transform.position.y;
  float posBase = (Physics.gravity.y * Mathf.Pow(distX, 2.0f)) / (2.0f * Mathf.Pow(speed, 2.0f));
  float posX = distX / posBase;
  float posY = (Mathf.Pow(posX, 2.0f) / 4.0f) - ((posBase - distY) / posBase);
  if (posY >= 0.0f)
  {
   if (拋射) //字段
    angleX = Mathf.Rad2Deg * Mathf.Atan(-posX / 2.0f + Mathf.Pow(posY, 0.5f));
   else
    angleX = Mathf.Rad2Deg * Mathf.Atan(-posX / 2.0f - Mathf.Pow(posY, 0.5f));
  }
  else
  {
   angleX = 45.0f;
  }
  return angleX;
 }
}