[Unity] 動かないオブジェクトの後ろに軌跡を出す

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

public class InvTrail : MonoBehaviour {
    [SerializeField] float m_spd=10f;
    [SerializeField] int m_positionCount = 50;
    LineRenderer m_lr;
    Vector3[] m_oldPos;
    int m_cnt;

    // Use this for initialization
    void Start () {
        m_lr = GetComponent<LineRenderer>();
        if (!m_lr)
            Destroy(this);

        m_lr.positionCount = m_positionCount;
        m_oldPos = new Vector3[m_lr.positionCount];
        for (int i = 0; i < m_oldPos.Length; ++i)
        {
            m_oldPos[i] = transform.position;
        }
        m_lr.SetPositions(m_oldPos);
        m_cnt = m_oldPos.Length - 1;
    }

    // Update is called once per frame
    void Update () {
        Vector3 wSpd = transform.rotation * Vector3.back * m_spd;
        m_cnt = Mathf.Max(0,m_cnt - 1);
        for (int i = m_oldPos.Length-1; i > m_cnt; --i)
        {
            m_oldPos[i] = m_oldPos[i-1]+wSpd*Time.deltaTime;
        }
        m_oldPos[m_cnt] = transform.position;
        m_lr.SetPositions(m_oldPos);
    }
}