private void DistanceRestrict()
    {
        if(Vector3.Distance(transform.position,lightPos.position)>maxDis)//maxDis是标量
        {
            Vector3 pos = (transform.position - lightPos.transform.position).normalize;//矢量
            pos *= maxDis;//矢量
            transform.position = pos + lightPos.position;

        }
    }