淡入（Fade in）：类似打开幕布

淡出（Fade out）：类似关上幕布

方案一  使用Dotween（推荐）

using DG.Tweening;
using UnityEngine;
using UnityEngine.UI;public class Test : MonoBehaviour
{public Image curtain;private float fadeTime = 1;private void Update(){if (Input.GetKeyDown(KeyCode.A)){SetAlpha(true);//测试淡入}if (Input.GetKeyDown(KeyCode.D)){SetAlpha(false);//测试淡出}}/// <summary>/// 设置淡入淡出/// </summary>/// <param name="isFadeIn">是否是淡入</param>private void SetAlpha(bool isFadeIn){curtain.DOFade(isFadeIn ? 0 : 1, fadeTime);}private void OnDisable(){curtain.DOKill();}
}

方案二 使用协程

using System.Collections;
using UnityEngine;
using UnityEngine.UI;public class Test : MonoBehaviour
{public Image fadePlane;private float fadeTime = 1;private void Update(){if (Input.GetKeyDown(KeyCode.A)){StartCoroutine(Fade(true));//测试淡入}if (Input.GetKeyDown(KeyCode.D)){StartCoroutine(Fade(false));//测试淡出}}IEnumerator Fade(bool isFadeIn){var from = fadePlane.color;var to = new Color(from.r, from.g, from.b, isFadeIn ? 0 : 1);float speed = 1 / fadeTime;float percent = 0;while (percent < 1){percent += Time.deltaTime * speed;fadePlane.color = Color.Lerp(from, to, percent);yield return null;}}
}

方案三  使用Animation(不推荐)