使用Unity3D制作游戏加载效果（协程）

using UnityEngine;
using System.Collections;
using UnityEngine.UI;
public class TestXXL : MonoBehaviour {
public Image img1;
public Image img2;
public Slider sld;
public Text txt;
public Button btn;
// Use this for initialization
void Start () {
sld.gameObject.SetActive(false);
btn.gameObject.SetActive(false);
StartCoroutine(CTR());
}

// Update is called once per frame
void Update () {

}

IEnumerator CTR()//主协程。商标图片消失后，滚动条激活，开始读条。读条结束后，激活开始按钮
{
yield return ChangeAlpha();
sld.gameObject.SetActive(true);
yield return ChangeValue();
btn.gameObject.SetActive(true);
}

IEnumerator ChangeAlpha()//随着时间改变Image（1）的透明度，使它慢慢覆盖住Image
{
while (img2.color.a<1)
{
img2.color += new Color(0, 0, 0, Time.deltaTime/3);
yield return 1;
}
}

IEnumerator ChangeValue()//随着时间改变滚动条的值，文本框中显示滚动条值得百分比
{
while (sld.value<1)
{
sld.value += Time.deltaTime / 3;
txt.text = Mathf.FloorToInt(sld.value*100) + "%";
yield return 1;
}
}
}