freecut/static/js/music.js

// FreeCut 程序化配乐生成器 —— 全部在浏览器端合成，无版权风险，人人免费使用
// 每种情绪生成一段可循环的纯音乐，作为内置配乐库
const MusicEngine = (() => {
  const cache = {};
  let _ctx = null;
  function ctx() {
    if (!_ctx) _ctx = new (window.AudioContext || window.webkitAudioContext)();
    return _ctx;
  }

  // 确定性伪随机（保证同一情绪每次生成一样，可循环）
  function makeRng(seed) {
    let s = seed >>> 0;
    return () => { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
  }

  // 定义：BPM / 根音(midi) / 调式 / 和弦进行(每小节1个和弦根音, 类型) / 琶音间隔 / 节奏感
  const MOODS = {
    warm:   { name: '温馨治愈', bpm: 74, root: 60, scale: 'major',  prog: [[60,'maj7'],[65,'maj7'],[67,'maj7'],[62,'maj7']], arp: 'full',   feel: 'pad' },
    fresh:  { name: '清新活力', bpm: 100, root: 62, scale: 'major',  prog: [[62,'maj7'],[60,'maj7'],[67,'maj7'],[65,'maj7']], arp: 'up',     feel: 'pluck' },
    epic:   { name: '激昂大片', bpm: 120, root: 57, scale: 'minor',  prog: [[57,'min'],[55,'min'],[60,'min'],[55,'min']], arp: 'drive',  feel: 'epic' },
    night:  { name: '深夜思绪', bpm: 70, root: 57, scale: 'minor',  prog: [[57,'min7'],[62,'maj7'],[55,'min7'],[60,'maj7']], arp: 'soft',   feel: 'lofi' },
    tech:   { name: '科技未来', bpm: 110, root: 64, scale: 'minor',  prog: [[64,'min'],[61,'min'],[66,'min'],[59,'min']], arp: 'seq',    feel: 'synth' },
    happy:  { name: '欢乐节奏', bpm: 118, root: 60, scale: 'major',  prog: [[60,'maj'],[65,'maj'],[60,'maj'],[67,'maj']], arp: 'bounce', feel: 'pop' },
  };

  const MAJOR = [0, 2, 4, 5, 7, 9, 11, 12];
  const MINOR = [0, 2, 3, 5, 7, 8, 10, 12];
  const CHORD = {
    'maj':  [0, 4, 7], 'maj7': [0, 4, 7, 11], 'min': [0, 3, 7],
    'min7': [0, 3, 7, 10], 'sus': [0, 5, 7], 'dim': [0, 3, 6],
  };

  function scaleOf(mood) { return mood.scale === 'minor' ? MINOR : MAJOR; }

  function generate(key, bars = 8) {
    const mood = MOODS[key];
    if (!mood) return null;
    const ac = ctx();
    const rng = makeRng(hashStr(key));
    const spb = 60 / mood.bpm;                 // 每拍秒数
    const secsPerBar = spb * 4;
    const total = secsPerBar * bars;
    const sr = ac.sampleRate;
    const buf = ac.createBuffer(2, Math.ceil(total * sr), sr);
    const sc = scaleOf(mood);
    const rootTone = mood.root;

    // 和弦根音序列
    const prog = mood.prog;
    const chords = [];
    for (let i = 0; i < bars; i++) {
      const [r, type] = prog[i % prog.length];
      const tones = CHORD[type].map(iv => r + 12 + iv); // 中音区
      chords.push(tones);
    }

    // 主旋律音阶池
    const pool = sc.map(iv => rootTone + 12 + iv).concat(sc.map(iv => rootTone + 24 + iv));
    const pool2 = sc.map(iv => rootTone + 12 + iv);

    // 旋律事件（每小节2-4个音）
    const melody = [];
    for (let b = 0; b < bars; b++) {
      const n = mood.feel === 'epic' ? 2 : mood.feel === 'lofi' ? 2 : 3 + (rng() > 0.5 ? 1 : 0);
      for (let i = 0; i < n; i++) {
        const beatPos = (i / n) * 4;
        const t = (b + beatPos / 4) * secsPerBar;
        let note;
        if (mood.feel === 'epic') {
          note = chords[b][0] + 12;                       // 根音高八度，宏大
        } else if (mood.feel === 'lofi') {
          note = pool[Math.floor(rng() * pool.length)];   // 慵懒随机
        } else {
          note = pool2[Math.floor(rng() * pool2.length)];
        }
        const dur = (spb * 4) / n * (0.75 + rng() * 0.4);
        melody.push({ t, note, dur, vel: 0.5 + rng() * 0.3 });
      }
    }

    // ---------- 渲染 ----------
    const L = buf.getChannelData(0), R = buf.getChannelData(1);
    const N = L.length;
    const add = (ch, from, dur, fn) => {
      const s0 = Math.max(0, Math.floor(from * sr));
      const n = Math.min(N - s0, Math.ceil(dur * sr));
      for (let i = 0; i < n; i++) {
        const t = i / sr;
        const v = fn(t);
        ch[s0 + i] += v;
      }
    };

    // 底鼓/军鼓简单节奏（确定性）
    for (let b = 0; b < bars; b++) {
      const t0 = b * secsPerBar;
      // 底鼓：每小节 4 拍
      for (let k = 0; k < 4; k++) {
        const t = t0 + k * spb;
        add(L, t, 0.25, tt => Math.sin(2 * Math.PI * (90 - tt * 160) * tt) * Math.exp(-tt * 14) * 0.5);
        add(R, t, 0.25, tt => Math.sin(2 * Math.PI * (90 - tt * 160) * tt) * Math.exp(-tt * 14) * 0.5);
      }
      // 军鼓/拍手：2、4拍，激昂时用
      if (mood.feel === 'epic' || mood.feel === 'pop' || mood.feel === 'drive') {
        for (const k of [1, 3]) {
          const t = t0 + k * spb;
          const noise = makeNoise(rng());
          add(L, t, 0.18, tt => noise(Math.floor(tt * 20000)) * Math.exp(-tt * 30) * 0.35);
          add(R, t, 0.18, tt => noise(Math.floor(tt * 20000)) * Math.exp(-tt * 30) * 0.35);
        }
      }
    }

    // 贝斯
    for (let b = 0; b < bars; b++) {
      const chRoot = mood.prog[b % mood.prog.length][0];
      for (let k = 0; k < 4; k++) {
        const t = b * secsPerBar + k * spb;
        const f = midiToFreq(chRoot - 12);
        add(L, t, spb * 0.9, tt => Math.sin(2 * Math.PI * f * tt) * Math.exp(-tt * 3.2) * 0.30);
        add(R, t, spb * 0.9, tt => Math.sin(2 * Math.PI * f * tt) * Math.exp(-tt * 3.2) * 0.30);
      }
    }

    // 和弦铺底
    for (let b = 0; b < bars; b++) {
      const tones = chords[b];
      const t = b * secsPerBar;
      for (const n of tones) {
        const f = midiToFreq(n);
        add(L, t, secsPerBar, tt => detuneSaw(tt, f) * env(tt, secsPerBar, 0.8, 0.5) * 0.055);
        add(R, t, secsPerBar, tt => detuneSaw(tt, f * 1.003) * env(tt, secsPerBar, 0.8, 0.5) * 0.055);
      }
    }

    // 主旋律
    for (const m of melody) {
      const f = midiToFreq(m.note);
      if (mood.feel === 'epic') {
        add(L, m.t, m.dur, tt => detuneSaw(tt, f) * env(tt, m.dur, 0.15, 0.6) * m.vel * 0.22);
        add(R, m.t, m.dur, tt => detuneSaw(tt, f * 1.002) * env(tt, m.dur, 0.15, 0.6) * m.vel * 0.22);
      } else if (mood.feel === 'lofi') {
        add(L, m.t, m.dur, tt => softTone(tt, f) * env(tt, m.dur, 0.2, 0.8) * m.vel * 0.35);
        add(R, m.t, m.dur, tt => softTone(tt, f) * env(tt, m.dur, 0.2, 0.8) * m.vel * 0.35);
      } else {
        // 琶音拨弦
        add(L, m.t, m.dur, tt => pluck(tt, f) * m.vel * 0.30);
        add(R, m.t, m.dur, tt => pluck(tt, f * 1.001) * m.vel * 0.30);
      }
    }

    // 归一化
    let peak = 0;
    for (let i = 0; i < N; i++) peak = Math.max(peak, Math.abs(L[i]), Math.abs(R[i]));
    if (peak > 0.95) {
      const g = 0.95 / peak;
      for (let i = 0; i < N; i++) { L[i] *= g; R[i] *= g; }
    }
    cache[key] = buf;
    return buf;
  }

  function hashStr(s) { let h = 5381; for (let i = 0; i < s.length; i++) h = ((h << 5) + h + s.charCodeAt(i)) >>> 0; return h; }
  function midiToFreq(m) { return 440 * Math.pow(2, (m - 69) / 12); }
  function env(t, dur, a, r) {
    const rel = Math.max(0.05, dur * r);
    if (t < a) return t / a;
    if (t > dur) return 0;
    return Math.max(0, 1 - (t - a) / rel);
  }
  function detuneSaw(t, f) {
    const p = (t * f) % 1;
    return 2 * p - 1;
  }
  function softTone(t, f) {
    const s = Math.sin(2 * Math.PI * f * t);
    return 0.6 * s + 0.4 * Math.sin(2 * Math.PI * f * 2 * t) * 0.5;
  }
  function pluck(t, f) {
    const d = Math.sin(2 * Math.PI * f * t) * Math.exp(-t * 6);
    const h = Math.sin(2 * Math.PI * f * 2.01 * t) * Math.exp(-t * 16) * 0.4;
    return d + h;
  }
  function makeNoise(rng) {
    const buf = new Float32Array(20000);
    for (let i = 0; i < buf.length; i++) buf[i] = rng() * 2 - 1;
    return idx => buf[Math.abs(idx) % buf.length];
  }

  // 获取（生成并缓存）配乐 AudioBuffer
  function getBuffer(key) {
    if (cache[key]) return Promise.resolve(cache[key]);
    // 稍等一帧，避免阻塞
    return new Promise(res => setTimeout(() => res(generate(key)), 30));
  }

  function list() {
    return Object.entries(MOODS).map(([k, v]) => ({ key: k, name: v.name, bpm: v.bpm }));
  }

  return { list, getBuffer, generate, ctx };
})();