unity 实时 获得屏幕中心点的世界坐标

Ray ray = Camera.main.ScreenPointToRay(new Vector3(Screen.width/2,Screen.height/2,0));//射线        RaycastHit hit;        if (Physics.Raycast(ray, out hit))//发射射线(射线，射线碰撞信息，射线长度，射线会检测的层级)        {            sphere.transform.position=new Vector3(hit.point.x,0,hit.point.z);        }