unity场景异步加载（进度条缓慢加载）_unity 进度条加载速度由慢到快

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.SceneManagement;
enum Phase3 { Start, Middle, End }
public class loading : MonoBehaviour
{
    static AsyncOperation async = null;
    public Text text;
    public Image Loading;
    [Tooltip("下个场景的名字，在Build Settings发布设置中需要先将该Scene加载进来才能识别！")]
    public string Scene_name;
    public Image float_tips;
    public float start_positon;
    public float end_positon;
    private Phase3 _phase = Phase3.Start;
    private float _progressValue = 0;
    private float START_LIMITER = 0.1f;
    private float _endStart = 0;
    private float _endValue = 0;
    private float MIDDLE_LIMITER = 1.0f;
    private float _middleValue = 0;
   //void Awake()
   // {
   //     Screen.SetResolution(1920,1080,true);
   // }
    void Start ()
    {      
        StartCoroutine(LoadScene());
    }
    // Update is called once per frame
    void Update ()
    {
        if (text && Loading && async != null)
        {
            if (this._phase == Phase3.Start)
            {
                // 正常
            }
            else if (this._phase == Phase3.Middle)
            {
                // 1秒加1个单位
                this.middle(Time.deltaTime);
            }
            else
            {
                // 1秒内从当前位置跳到结束
                this.end(Time.deltaTime);
            }
            text.text = ( (int)( _progressValue * 100 ) ).ToString() + "%";
            Loading.fillAmount = _progressValue;
            float_tips.GetComponent<RectTransform>().localPosition = new Vector3(start_positon + end_positon * _progressValue, float_tips.GetComponent<RectTransform>().localPosition.y, 0);         
            //temp = Mathf.Lerp(temp, async.progress, Time.deltaTime);
            //text.text = ( (int)( temp * 100 * 10 / 9 ) ).ToString() + "%";
            //Loading.fillAmount = temp * 10 / 9;
            if (this._progressValue >= 1)
            {
                async.allowSceneActivation = true;
            }
            //Debug.Log(timer);
            //if (temp / 9 * 10 >= 0.95)
            //{
            //    text.text = 100.ToString() + "%";
            //    Loading.fillAmount = 1;
            //    asyn.allowSceneActivation = true;
            //}
        }
    }
    private void middle (float delta_time)
    {
        this._middleValue += delta_time;
        if (this._middleValue >= MIDDLE_LIMITER)
        {
            this._middleValue -= MIDDLE_LIMITER;
            if (this._progressValue < 0.99f)
            {
                this._progressValue += 0.01f;
            }
        }
    }
    private void end (float delta_time)
    {
        this._endValue += delta_time;
        this._progressValue = Mathf.Lerp(this._endStart, 1, this._endValue);
    }
    IEnumerator LoadScene ()
    {
        //异步读取场景。
        async = SceneManager.LoadSceneAsync(Scene_name);
        async.allowSceneActivation = false;
        while (async.progress < 0.9f)
        {
            Debug.Log(async.progress);
            //Debug.Log(async.progress + "----" + (async.progress <= 0.9f));
            if (async.progress <= START_LIMITER)
            {
                this._progressValue = async.progress;
            }
            else
            {
                this._phase = Phase3.Middle;
            }
            yield return null;
        }
        this._phase = Phase3.End;
        this._endStart = this._progressValue;
        //while (_progressValue < 1)
        //{
        //    yield return new WaitForEndOfFrame();
        //}
        //Debug.LogWarning(_progressValue);
        yield return async;
    }
}