fnl/Assets/MusicFadeController.cs

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

public class MusicFadeController : MonoBehaviour {
    [SerializeField] public AudioSource audioSource;
    public bool shouldLoop = false;
    public float originalVolume = 1;

    // Keeps track of the most recent fade command.
    // Previous fades should stop as soon as the actionCounter increments.
    public int actionCounter = 0;

    // Credit: https://forum.unity.com/threads/fade-out-audio-source.335031/
    public IEnumerator IFadeIn(float time) {
        int cache = ++actionCounter;
        audioSource.volume = 0;
        while (audioSource.volume < originalVolume && actionCounter == cache) {
            audioSource.volume += originalVolume * Time.deltaTime / time;
            yield return null;
        }
        // Skip if preempted
        if (cache != actionCounter)
            yield break;

        audioSource.volume = originalVolume;
    }

    // Credit: https://forum.unity.com/threads/fade-out-audio-source.335031/
    IEnumerator IFadeOut(float time) {
        int cache = ++actionCounter;
        audioSource.volume = originalVolume;
        while (audioSource.volume > 0 && actionCounter == cache) {
            audioSource.volume -= originalVolume * Time.deltaTime / time;
            yield return null;
        }
        // Skip if preempted
        if (cache != actionCounter)
            yield break;

        audioSource.Stop();
        shouldLoop = false;
        audioSource.volume = originalVolume;
    }

    IEnumerator IFadeOutThenIn(float outTime, float inTime, AudioClip loopClip) {
        int cache = ++actionCounter;
        if (audioSource.isPlaying) {
            audioSource.volume = originalVolume;
            while (audioSource.volume > 0 && actionCounter == cache) {
                audioSource.volume -= originalVolume * Time.deltaTime / outTime;
                yield return null;
            }
            // Skip if preempted
            if (cache != actionCounter)
                yield break;

            audioSource.Stop();
        }

        audioSource.volume = 0;
        audioSource.clip = loopClip;
        audioSource.Play();

        while (audioSource.volume < originalVolume && actionCounter == cache) {
            audioSource.volume += originalVolume * Time.deltaTime / inTime;
            yield return null;
        }
        // Skip if preempted
        if (cache != actionCounter)
            yield break;

        audioSource.volume = originalVolume;
    }

    public void ChangeVolume(float volume) {
        audioSource.volume = originalVolume = volume;
    }

    public void FadeIn(float time) {
        StartCoroutine(IFadeIn(time));
    }

    public void FadeOut(float time) {
        StartCoroutine(IFadeOut(time));
    }

    public void FadeOutThenIn(float o, float i, AudioClip loopClip) {
        StartCoroutine(IFadeOutThenIn(o, i, loopClip));
    }

    IEnumerator PlayLoopAfter(float time, AudioClip loopClip) {
        yield return new WaitForSeconds(time);
        if (shouldLoop) {
            audioSource.clip = loopClip;
            audioSource.Play();
        }
    }

    public void PlayMainMenuLoopAfter(float time, AudioClip loopClip) {
        StartCoroutine(PlayLoopAfter(time, loopClip));
    }

    // Start is called before the first frame update
    void Start()
    {
        originalVolume = audioSource.volume;
    }

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