增加低通效果开关

- 引入DoTween
- 实现功能

Assets/Scripts/OCES/Audio/HandWritten/AudioSystem.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.Linq;
 using UnityEngine;
 using UnityEngine.Audio;
+using DG.Tweening;
 
 namespace OCES.Audio
 {
@@ -19,6 +20,7 @@ namespace OCES.Audio
         AudioObjectConfig m_audioObjects;
         AudioGroupConfig m_groups;
         AudioMixer m_mixer;
+        Tween m_lowpassTween;
 
         // ─────────────────────────────────────────────
         // 公开接口
@@ -41,6 +43,34 @@ namespace OCES.Audio
             // TODO: 按文件名播放
         }
 
+        public void SetLowpass(bool enable)
+        {
+            float target = enable ? 440f : 22000f;
+
+            // Kill existing tween to avoid stacking
+            if (this.m_lowpassTween != null && this.m_lowpassTween.IsActive())
+                this.m_lowpassTween.Kill();
+
+            // Get current value as start
+            if (!this.m_mixer.GetFloat("LowpassFreq", out float current))
+                current = target;
+
+            float startLog = Mathf.Log10(current);
+            float endLog = Mathf.Log10(target);
+            
+            this.m_lowpassTween = DOTween.To(
+                () => startLog,
+                x =>
+                {
+                    startLog = x;
+                    float value = Mathf.Pow(10f, startLog);
+                    this.m_mixer.SetFloat("LowpassFreq", value);
+                },
+                endLog,
+                0.2f // duration in seconds
+            ).SetEase(Ease.OutCubic);
+        }
+
         /// <summary>
         /// 更新游戏状态，驱动音乐与环境音系统切换。
         /// 调用示例：AudioSystem.Instance.SetState(GameState.Game);