부모를 잃은 Trail fade out

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

public class TrailFadeOut : MonoBehaviour {
    [SerializeField, Range(0f,1f)] float forrowRate = 0f;
    [SerializeField, Range(0.1f, 4f)] float fadeTime = 1f;
    Coroutine coro;
    TrailRenderer trail;
    Vector3 oldPos;

    // Use this for initialization
    void Start () {
        coro = null;
        trail = GetComponent<TrailRenderer>();
        oldPos = transform.position;
    }

    // Update is called once per frame
    void Update () {
        if(transform.parent==null){
            if (coro == null){
                Vector3 spd = (transform.position - oldPos) / Time.deltaTime;
                coro = StartCoroutine(trailFadeCo(spd));
            }
        }else{
            oldPos = transform.position;
        }
    }

    IEnumerator trailFadeCo(Vector3 _spd){
        Color defCol = trail.material.GetColor("_TintColor");
        Color col = defCol;
        yield return null;
        while(col.a>0f){
            col.a = Mathf.Max(col.a-Time.deltaTime/fadeTime, 0f);
            trail.material.SetColor("_TintColor",col);
            transform.position += _spd * forrowRate * Time.deltaTime;
            yield return null;
        }
        Destroy(gameObject);
    }
}

trail.material.SetColor("_TintColor",col);

trail.material.color = col