unity实现鼠标拖住3D物体

using System.Collections;using System.Collections.Generic;using UnityEngine;public class ModelDrages : MonoBehaviour {//发射射线的摄像机private Camera cam;//射线碰撞的物体private GameObject go;//射线碰撞物体的名字public static string btnName;private Vector3 screenSpace;private Vector3 offset;private bool isDrage = false;// Use this for initializationvoid Start (){ cam = Camera.main;}// Update is called once per frame void Update (){ //整体初始位置 Ray ray = cam.ScreenPointToRay(Input.mousePosition); //从摄像机发出到点击坐标的射线 RaycastHit hitInfo; if (isDrage == false) {  if(Physics .Raycast (ray,out hitInfo))  {   //划出射线 只有在Scene视图中才能看到   Debug.DrawLine(ray.origin, hitInfo.point);   go = hitInfo.collider.gameObject;   print(btnName);   screenSpace = cam.WorldToScreenPoint(go.transform.position);   offset = go.transform.position - cam.ScreenToWorldPoint(new Vector3(Input.mousePosition.x, Input.mousePosition.y, Input.mousePosition.z));   //物体的名字   btnName = go.name;   //组件的名字  }  else  {   btnName = null;  } } if(Input.GetMouseButton(0)) {  Vector3 currentScreenSpace = new Vector3(Input.mousePosition.x, Input.mousePosition.y, screenSpace.z);  Vector3 currentPosition = cam.ScreenToWorldPoint(currentScreenSpace) + offset;  if (btnName != null)  {   go.transform.position = currentPosition;  }  isDrage = true; } else {  isDrage = false; } }}