unity3D实现三维物体跟随鼠标

using UnityEngine;
/*
 让物体完全跟随鼠标
  */
public class MouseMove : MonoBehaviour
{
 [Header("主相机")]
 [Tooltip("主相机")]
 /// <summary>
 /// 主相机
 /// </summary>
 public Camera m_mainCamera;
 [Header("目标物体")]
 [Tooltip("目标物体")]
 /// <summary>
 /// 目标物体
 /// </summary>
 public Transform m_target;
 
 void Start()
 {
  isDown = false;
  targetWTSP = m_mainCamera.WorldToScreenPoint(m_target.position);
 }
 /// <summary>
 /// 是否按下
 /// </summary>
 private bool isDown;
 /// <summary>
 /// 记录初始化时候target世界坐标转屏幕坐标时候的位置 WTSP==WorldToScreenPoint
 /// </summary>
 private Vector3 targetWTSP;
 void Update()
 {
  if (Input.GetMouseButtonDown(0)) {
   isDown = true;
  }
  if (Input.GetMouseButtonUp(0))
  {
   isDown = false;
  }
 }
 private void LateUpdate()
 {
  if (isDown)
  {
   Vector3 mouseVec3 = m_mainCamera.ScreenToWorldPoint(
    new Vector3(Input.mousePosition.x, Input.mousePosition.y, targetWTSP.z)
   );
   m_target.position = mouseVec3;
  }
 }
}