hellbound/Assets/Scripts/Game/UI/BackgroundController.cs

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

public class BackgroundController : MonoBehaviour
{
    [SerializeField] private Image _backgroundImage;
    [SerializeField] [Range(0, 1)] private float _maxBackgroundAlpha = .787f;

    [SerializeField] private AnimationCurve _showCurve;
    [SerializeField] private AnimationCurve _hideCurve;

    [SerializeField] private float _showTime;
    [SerializeField] private float _hideTime;

    private Coroutine _showHandle;
    private Coroutine _hideHandle;

    private bool _showInProgress;
    private bool _hideInProgress;

    private float _currentProgress;

    public void Init()
    {
        SetAlpha(_backgroundImage, 0);
        _backgroundImage.enabled = false;
    }

    public void Show()
    {
        if (_showInProgress)
            return;

        if (_hideInProgress)
        {
            StopCoroutine(_hideHandle);
            _hideInProgress = false;
            _showHandle = StartCoroutine(ShowCoroutine(1 - _currentProgress));
            return;
        }

        _showHandle = StartCoroutine(ShowCoroutine(0));
    }

    public void Hide()
    {
        if (_hideInProgress)
            return;

        if (_showInProgress)
        {
            StopCoroutine(_showHandle);
            _showInProgress = false;
            _hideHandle = StartCoroutine(HideCoroutine(1 - _currentProgress));
            return;
        }

        _hideHandle = StartCoroutine(HideCoroutine(0));
    }

    private IEnumerator ShowCoroutine(float start_progress)
    {
        _showInProgress = true;
        _backgroundImage.enabled = true;
        yield return Toggle(start_progress, _showCurve, _showTime, 0, _maxBackgroundAlpha);
        _showInProgress = false;
    }

    private IEnumerator HideCoroutine(float start_progress)
    {
        _hideInProgress = true;
        yield return Toggle(start_progress, _hideCurve, _hideTime, _maxBackgroundAlpha, 0);
        _backgroundImage.enabled = false;
        _hideInProgress = false;
    }

    private IEnumerator Toggle(float start_progress, AnimationCurve curve, float toggle_time, float start_value, float end_value)
    {
        _currentProgress = start_progress;

        var time = _currentProgress * toggle_time;

        while (time < toggle_time)
        {
            _currentProgress = time / toggle_time;

            var alpha = Mathf.LerpUnclamped(start_value, end_value, curve.Evaluate(_currentProgress));
            SetAlpha(_backgroundImage, alpha);

            time += Time.deltaTime;
            yield return null;
        }

        SetAlpha(_backgroundImage, end_value);
    }

    private void SetAlpha(Image img, float alpha)
    {
        Color imgColor = img.color;
        imgColor.a = alpha;

        img.color = imgColor;
    }
}