计算敌人在屏幕中的位置

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;

public class CArrowLockAt : MonoBehaviour
{
    public Transform target;    //目标
    public Transform self;  //自己
    public Image RoundScope;//指定为圆
    public float direction; //箭头旋转的方向，或者说角度，只有正的值
    public Vector3 u;   //叉乘结果，用于判断上述角度是正是负

    float devValue =100f;   //离屏边缘距离
  

    Quaternion originRot;   //箭头原角度

    // 初始化
    void Start()
    {
        originRot = transform.rotation;
    }

    void Update()
    {


        // 计算向量和角度
        Vector3 forVec = self.forward;  //计算本物体的前向量
        Vector3 angVec = (target.position - self.position).normalized;  //本物体和目标物体之间的单位向量

        #region 求指向
        Vector3 targetVec = Vector3.ProjectOnPlane(angVec - forVec, forVec).normalized; //这步很重要，将上述两个向量计算出一个代表方向的向量后投射到本身的xy平面
        Vector3 originVec = self.up;

        direction = Vector3.Dot(originVec, targetVec);  //再跟y轴正方向做点积和叉积，就求出了箭头需要旋转的角度和角度的正负

        u = Vector3.Cross(originVec, targetVec);
       
        direction = Mathf.Acos(direction) * Mathf.Rad2Deg;  //转换为角度

        u = self.InverseTransformDirection(u);  //叉积结果转换为本物体坐标
      
        // 给与旋转值
        transform.rotation = originRot * Quaternion.Euler(new Vector3(0f, 0f, direction * (u.z > 0 ? 1 : -1)));
        #endregion


        // 计算当前物体在屏幕上的位置
        Vector2 screenPos = RectTransformUtility.WorldToScreenPoint(Camera.main,target.position);
        #region 求在圆边位置
        //圆半径
        float range = (RoundScope.rectTransform.sizeDelta.y / 2) - 30;
        //目标位置
        Vector3 cc = RoundScope.transform.position + Vector3.ProjectOnPlane((target.position - self.position) - self.forward, self.forward) * range;
        #endregion
        // 不在屏幕内的情况
        if (screenPos.x < devValue || screenPos.x > Screen.width - devValue || screenPos.y < devValue || screenPos.y > Screen.height - devValue || Vector3.Dot(forVec, angVec) < 0)
        {
            if (range < Vector3.Distance(cc, RoundScope.rectTransform.position))
            {
                transform.position = (cc - RoundScope.transform.position).normalized * range + RoundScope.transform.position;
            }
            else
            {
                transform.position = cc;
            }
        }
        else    // 在屏幕内的情况
        {
            transform.Rotate(0, 90, -45);
        }
    }
}