JJBB/Assets/Project/Script/RawImageAlpha.cs

using UnityEngine;
using System.Collections;
using UnityEngine.UI;

public class RawImageAlpha : MonoBehaviour {

    public bool PlayOnAwake = false;
    public RawImage m_RawImage;
    public float delayTime = 1;
    public float durTime = 1;
    private float Startime = 0;
    public float StartAlpha;
    public float EndAlpha;

    void Awake()
    {
        if (m_RawImage == null || m_RawImage.texture == null)
        {
            gameObject.SetActive(false);
            return;
        }
    }

    private void Start()
    {
        if(PlayOnAwake)
        {
            Startime = Time.time;
            Update();
        }
    }

    public void SetStart(float startAlpha,float endAlpha,float durtion = 1,float delay = 0)
    {
        delayTime = Time.time + delay;
        durTime = durtion;
        StartAlpha = startAlpha;
        EndAlpha = endAlpha;
        Startime = Time.time + delay;
        Update();
    }

    void Update()
    {
        if (Startime <= 0 || m_RawImage==null)
            return;
        if(Time.time - delayTime < 0)
        {
            return;
        }
        float rate = (Time.time - Startime) / durTime;
        if(rate > 1 || rate < 0)
        {
            Startime = 0;
            return;
        }
        Color newColor = m_RawImage.color;
        newColor.a = Mathf.Lerp(StartAlpha, EndAlpha, rate);
        m_RawImage.color = newColor;
    }

}