using UnityEngine;

public class GunFollowMouse : MonoBehaviour {
  public RectTransform UGUICanvas;
  public Camera mainCamera;
  //攝像機旋轉(zhuǎn)的緩動速率
  private float rotateSpeed = 5;
  void Start () {
 
 }
 
 void Update () {
    //定義一個世界坐標的鼠標點
    Vector3 mousePos;
    //獲取當前canvas下鼠標的二維坐標點 轉(zhuǎn)化為三維 out出來
    RectTransformUtility.ScreenPointToWorldPointInRectangle(UGUICanvas,
      new Vector2(Input.mousePosition.x, Input.mousePosition.y),
      mainCamera, out mousePos
      );
    //炮臺的旋轉(zhuǎn)角度
    float angle;
    //向量dirMouse為鼠標的向量減去槍的起始向量得到槍到鼠標位置的方向向量
    Vector3 dirMouse = mousePos - transform.position;
    angle = Vector3.Angle(dirMouse, Vector3.up);//直接得到兩個向量之間的夾角,這個角度是沒有正負的
    if (mousePos.x > transform.position.x)
    {
      angle = - angle;
    }
    transform.localRotation = Quaternion.Lerp(transform.localRotation, Quaternion.Euler(0, 0, angle)
      , Time.deltaTime * rotateSpeed);
 }
}