feat(audio): 重写BGM为轻快chiptune风格，BPM128 C大调，4层结构（鼓+低音+旋律+装饰）

game/AudioEngine.ts

@@ -230,8 +230,9 @@ export class AudioEngine {
   // ─── 背景音乐 ────────────────────────────────────────────────────────────────
 
   /**
-   * 启动背景音乐（办公室 ambient：低频嗡鸣 + 轻微节奏脉冲）
+   * 启动背景音乐
-   * 完全程序化合成，循环播放
+   * 风格：轻快 chiptune / 像素塔防，BPM=128，C大调，4层结构
+   * 完全程序化合成，无音频文件依赖
    */
   startBGM(): void {
     if (!this.ac || this.bgmRunning) return
@@ -249,41 +250,170 @@ export class AudioEngine {
 
   private _scheduleBGM(): void {
     if (!this.ac || !this.bgmRunning) return
-    const t = this.ac.currentTime
+    const ac = this.ac
+    const t = ac.currentTime
 
-    // 底层办公室嗡鸣（电脑风扇感）
+    const BPM = 128
-    const droneGain = this.ac.createGain()
+    const beat = 60 / BPM          // 0.469s / 拍
-    droneGain.gain.value = 0.04
+    const bar  = beat * 4           // 1.875s / 小节
-    droneGain.connect(this.masterGain)
+    const BARS = 8                  // 循环 8 小节
-    const drone = this.ac.createOscillator()
+    const loopLen = bar * BARS      // ≈ 15s
-    drone.type = 'sawtooth'
-    drone.frequency.setValueAtTime(55, t)
-    drone.frequency.linearRampToValueAtTime(58, t + 8)
-    drone.frequency.linearRampToValueAtTime(55, t + 16)
-    drone.connect(droneGain)
-    drone.start(t)
-    drone.stop(t + 16)
-    this.bgmNodes.push(drone)
 
-    // 低频键盘噪声节拍（每 0.8s 一拍）
+    // ── 辅助：创建带 Gain 的振荡器，自动连接到 masterGain ──────────────────
-    for (let i = 0; i < 20; i++) {
+    const addOsc = (
-      const beat = t + i * 0.8
+      type: OscillatorType,
-      const ng = this.ac.createGain()
+      freq: number,
-      ng.gain.setValueAtTime(0.03, beat)
+      start: number,
-      ng.gain.exponentialRampToValueAtTime(0.001, beat + 0.15)
+      end: number,
-      ng.connect(this.masterGain)
+      vol: number,
-      const ns = this.ac.createOscillator()
+      freqEnd?: number
-      ns.type = 'square'
+    ): void => {
-      ns.frequency.value = i % 4 === 0 ? 130 : i % 2 === 0 ? 110 : 87
+      const g = ac.createGain()
-      ns.connect(ng)
+      g.gain.setValueAtTime(vol, start)
-      ns.start(beat)
+      g.gain.exponentialRampToValueAtTime(0.0001, end)
-      ns.stop(beat + 0.12)
+      g.connect(this.masterGain)
-      this.bgmNodes.push(ns)
+      const o = ac.createOscillator()
+      o.type = type
+      o.frequency.setValueAtTime(freq, start)
+      if (freqEnd !== undefined) {
+        o.frequency.linearRampToValueAtTime(freqEnd, end)
+      }
+      o.connect(g)
+      o.start(start)
+      o.stop(end)
+      this.bgmNodes.push(o)
     }
 
-    // 16s 后循环
+    // ── 辅助：创建打击音（noise burst） ────────────────────────────────────
+    const addDrum = (start: number, dur: number, vol: number, hp = 0): void => {
+      const bufLen = Math.ceil(ac.sampleRate * dur)
+      const buf = ac.createBuffer(1, bufLen, ac.sampleRate)
+      const d = buf.getChannelData(0)
+      for (let i = 0; i < bufLen; i++) d[i] = Math.random() * 2 - 1
+      const src = ac.createBufferSource()
+      src.buffer = buf
+      const g = ac.createGain()
+      g.gain.setValueAtTime(vol, start)
+      g.gain.exponentialRampToValueAtTime(0.0001, start + dur)
+      if (hp > 0) {
+        const f = ac.createBiquadFilter()
+        f.type = 'highpass'
+        f.frequency.value = hp
+        src.connect(f); f.connect(g)
+      } else {
+        src.connect(g)
+      }
+      g.connect(this.masterGain)
+      src.start(start)
+      src.stop(start + dur)
+    }
+
+    // ── 音符频率表（C4 = 261.63 Hz） ──────────────────────────────────────
+    // C4  D4  E4  F4  G4  A4  B4  C5  D5  E5  G5
+    const N: Record<string, number> = {
+      C4: 261.63, D4: 293.66, E4: 329.63, F4: 349.23,
+      G4: 392.00, A4: 440.00, B4: 493.88,
+      C5: 523.25, D5: 587.33, E5: 659.25, G5: 783.99,
+      // 低八度
+      C3: 130.81, E3: 164.81, F3: 174.61, G3: 196.00, A3: 220.00,
+    }
+
+    // ═══════════════════════════════════════════════════════════════
+    // 层 1：底鼓 + 军鼓（kick on 1,3；snare on 2,4）
+    // ═══════════════════════════════════════════════════════════════
+    for (let b = 0; b < BARS * 4; b++) {
+      const st = t + b * beat
+      const pos = b % 4  // 每小节内位置 0-3
+
+      if (pos === 0 || pos === 2) {
+        // Kick：低频 sine 扫频（100→30Hz）+ noise burst
+        addOsc('sine', 100, st, st + 0.18, 0.45, 30)
+        addDrum(st, 0.12, 0.12, 0)
+      }
+      if (pos === 1 || pos === 3) {
+        // Snare：中频 noise + 轻微 sine
+        addDrum(st, 0.1, 0.18, 800)
+        addOsc('sine', 220, st, st + 0.07, 0.08)
+      }
+      // Hi-hat 每半拍（8 分音符）
+      addDrum(st,            0.05, 0.07, 6000)
+      addDrum(st + beat / 2, 0.04, 0.05, 6000)
+    }
+
+    // ═══════════════════════════════════════════════════════════════
+    // 层 2：和弦低音线 (square, 低八度)
+    // 进行：C - F - G - C - Am - F - G - C
+    // ═══════════════════════════════════════════════════════════════
+    const bassChord = [
+      N.C3, N.F3, N.G3, N.C3,
+      N.A3, N.F3, N.G3, N.C3,
+    ]
+    for (let b = 0; b < BARS; b++) {
+      const st = t + b * bar
+      const freq = bassChord[b]
+      // 每小节 4 拍低音 arpeggio（根音每拍重复）
+      for (let i = 0; i < 4; i++) {
+        addOsc('square', freq, st + i * beat, st + i * beat + beat * 0.8, 0.1)
+      }
+      // 五度音（和声感）
+      addOsc('triangle', freq * 1.5, st, st + bar * 0.9, 0.035)
+    }
+
+    // ═══════════════════════════════════════════════════════════════
+    // 层 3：主旋律（triangle，亮而柔和，8小节 melody）
+    // 轻快的 C 大调旋律，8小节/32拍
+    // ═══════════════════════════════════════════════════════════════
+    // 每项：[频率, 持续拍数]
+    const melody: [number, number][] = [
+      // 小节 1-2：上行跳跃
+      [N.E4, 0.5], [N.G4, 0.5], [N.C5, 1], [N.B4, 0.5], [N.A4, 0.5],
+      [N.G4, 1],   [N.A4, 0.5], [N.G4, 0.5],
+      // 小节 3-4：中段装饰
+      [N.E4, 0.5], [N.F4, 0.5], [N.G4, 1], [N.E4, 0.5], [N.D4, 0.5],
+      [N.C4, 1],   [N.D4, 0.5], [N.E4, 0.5],
+      // 小节 5-6：高潮段
+      [N.G4, 0.5], [N.A4, 0.5], [N.C5, 1], [N.D5, 0.5], [N.C5, 0.5],
+      [N.B4, 1],   [N.A4, 0.5], [N.G4, 0.5],
+      // 小节 7-8：收尾回落
+      [N.E4, 0.5], [N.D4, 0.5], [N.C4, 0.5], [N.E4, 0.5],
+      [N.G4, 0.5], [N.F4, 0.5], [N.E4, 0.5], [N.D4, 0.5],
+      [N.C4, 1.5], [0, 0.5],
+    ]
+    let melodyT = t
+    for (const [freq, dur] of melody) {
+      const durSec = dur * beat
+      if (freq > 0) {
+        addOsc('triangle', freq, melodyT, melodyT + durSec * 0.85, 0.18)
+        // 加一层八度泛音（更亮更饱满）
+        addOsc('sine', freq * 2, melodyT, melodyT + durSec * 0.6, 0.06)
+      }
+      melodyT += durSec
+    }
+
+    // ═══════════════════════════════════════════════════════════════
+    // 层 4：装饰音（高八度 sine 短促音符，活跃感）
+    // 每2小节出现一次 arpegio 装饰
+    // ═══════════════════════════════════════════════════════════════
+    const decoPattern = [
+      // 小节2结尾装饰
+      { st: t + bar * 1.75, notes: [N.C5, N.E5, N.G5] },
+      // 小节4结尾装饰
+      { st: t + bar * 3.75, notes: [N.G4, N.C5, N.E5] },
+      // 小节6结尾装饰
+      { st: t + bar * 5.75, notes: [N.C5, N.D5, N.E5] },
+    ]
+    for (const { st, notes } of decoPattern) {
+      notes.forEach((freq, i) => {
+        addOsc('sine', freq, st + i * 0.08, st + i * 0.08 + 0.12, 0.1)
+      })
+    }
+
+    // 循环调度
     setTimeout(() => {
-      if (this.bgmRunning) this._scheduleBGM()
+      if (this.bgmRunning) {
-    }, 15500)
+        this.bgmNodes = []
+        this._scheduleBGM()
+      }
+    }, (loopLen - 0.3) * 1000)
   }
 }