web/engine.js

// AIRWAVES live engine. Three looping stems -> per-stem gain -> shared lowpass
// filter -> [dry through a stutter GATE] + [reverb send] + [delay send] -> master
// -> analyser -> out. Hands drive the params directly (zero model in this path),
// always via setTargetAtTime so the bend is buttery and never clicks.
import { renderStems, makeIR, LOOP_LEN, BEAT } from "./groove.js";

export class AudioEngine {
  constructor() {
    this.ctx = null; this.sources = []; this.ready = false; this.playing = false;
    this._stutter = 0; this._gateT = 0; this._sched = null;
    this.mode = "beat";          // "beat" (built-in, full control) | "stream" (captured tab)
    this.extSource = null; this.extStream = null;
  }

  async init() {
    this.ctx = new (window.AudioContext || window.webkitAudioContext)();
    const ctx = this.ctx;
    this.buffers = await renderStems();

    this.master = ctx.createGain(); this.master.gain.value = 0.9;
    this.analyser = ctx.createAnalyser(); this.analyser.fftSize = 256; this.analyser.smoothingTimeConstant = 0.78;

    this.filter = ctx.createBiquadFilter();
    this.filter.type = "lowpass"; this.filter.frequency.value = 18000; this.filter.Q.value = 7;

    this.gate = ctx.createGain(); this.gate.gain.value = 1;          // dry path + stutter gate

    this.convolver = ctx.createConvolver(); this.convolver.buffer = makeIR(ctx, 2.0);
    this.reverbSend = ctx.createGain(); this.reverbSend.gain.value = 0;

    this.delay = ctx.createDelay(1.0); this.delay.delayTime.value = BEAT / 2;
    this.fb = ctx.createGain(); this.fb.gain.value = 0.36;
    this.delay.connect(this.fb); this.fb.connect(this.delay);
    this.delaySend = ctx.createGain(); this.delaySend.gain.value = 0;

    this.stemGain = {};
    this._mix = { drums: 1.0, bass: 0.92, melody: 0.5 };   // drums lead, marimba underneath
    for (const name of Object.keys(this.buffers)) {
      const g = ctx.createGain(); g.gain.value = this._mix[name] ?? 1; g.connect(this.filter);
      this.stemGain[name] = g;
    }

    this.filter.connect(this.gate);        this.gate.connect(this.master);          // dry
    this.filter.connect(this.reverbSend);  this.reverbSend.connect(this.convolver); this.convolver.connect(this.master);
    this.filter.connect(this.delaySend);   this.delaySend.connect(this.delay);      this.delay.connect(this.master);
    this.master.connect(this.analyser);    this.analyser.connect(ctx.destination);

    this.ready = true;
  }

  play() {
    if (!this.ready || this.playing) return;
    const ctx = this.ctx;
    if (ctx.state === "suspended") ctx.resume();
    const t0 = ctx.currentTime + 0.12;     // shared start => phase-locked stems
    this.sources = [];
    for (const [name, buf] of Object.entries(this.buffers)) {
      const src = ctx.createBufferSource();
      src.buffer = buf; src.loop = true; src.loopStart = 0; src.loopEnd = LOOP_LEN;
      src.connect(this.stemGain[name]); src.start(t0);
      this.sources.push(src);
    }
    this.playing = true; this._gateT = t0;
    this._sched = setInterval(() => this._tick(), 25);
  }

  // ---- hand-driven params ----
  setFilter(t01) {            // hero: hand height -> cutoff (exp 180Hz..18kHz)
    const f = 180 * Math.pow(18000 / 180, Math.max(0, Math.min(1, t01)));
    this.filter.frequency.setTargetAtTime(f, this.ctx.currentTime, 0.04);
  }
  setSpace(wet) {             // pinch -> reverb + delay send
    this.reverbSend.gain.setTargetAtTime(wet * 0.9, this.ctx.currentTime, 0.06);
    this.delaySend.gain.setTargetAtTime(wet * 0.5, this.ctx.currentTime, 0.06);
  }
  setWarp(t01) {              // roll -> turntable warp (tempo + pitch coupled), 0.5x..1.5x
    if (this.mode !== "beat") return;   // can't time-stretch a live captured stream
    const rate = 0.5 + t01;   // t01 0..1 -> 0.5..1.5
    for (const s of this.sources) s.playbackRate.setTargetAtTime(rate, this.ctx.currentTime, 0.06);
  }
  setStutter(amount) { this._stutter = amount; }   // fist -> gate chop intensity
  crossfade(t01) {            // two-hand: drums (0) <-> melody (1)
    if (!this.stemGain.drums) return;
    this.stemGain.drums.gain.setTargetAtTime(0.55 + (1 - t01) * 0.45, this.ctx.currentTime, 0.08);
    this.stemGain.melody.gain.setTargetAtTime(0.28 + t01 * 0.5, this.ctx.currentTime, 0.08);
  }
  drop() {                    // fist-release: slam open + a momentary push
    const ctx = this.ctx, now = ctx.currentTime;
    this.gate.gain.cancelScheduledValues(now); this.gate.gain.setValueAtTime(1, now);
    this.master.gain.cancelScheduledValues(now);
    this.master.gain.setValueAtTime(1.25, now);
    this.master.gain.exponentialRampToValueAtTime(0.9, now + 0.5);
  }
  duck(level = 0.4, hold = 1.0) {   // dip the music so the hype-man cuts through
    const g = this.master.gain, now = this.ctx.currentTime;
    g.cancelScheduledValues(now);
    g.setTargetAtTime(0.9 * level, now, 0.04);
    g.setTargetAtTime(0.9, now + hold, 0.12);
  }

  // ---- input source: bend a captured browser tab (YouTube, SoundCloud…) ----
  async captureTab() {
    // Chrome shows the tab/screen picker; user ticks "Share tab audio".
    // suppressLocalAudioPlayback mutes the original so only the BENT mix is heard.
    const stream = await navigator.mediaDevices.getDisplayMedia({
      video: true,
      audio: { suppressLocalAudioPlayback: true, echoCancellation: false, noiseSuppression: false, autoGainControl: false },
    });
    stream.getVideoTracks().forEach((t) => t.stop());   // we only want the audio
    if (!stream.getAudioTracks().length) {
      stream.getTracks().forEach((t) => t.stop());
      throw new Error("No tab audio — re-share a Chrome tab and tick “Share tab audio”.");
    }
    this._teardownExt();
    this.extStream = stream;
    this.extSource = this.ctx.createMediaStreamSource(stream);
    this.extSource.connect(this.filter);                // into the same bend chain
    for (const g of Object.values(this.stemGain)) g.gain.setTargetAtTime(0, this.ctx.currentTime, 0.05);
    this.mode = "stream";
    stream.getAudioTracks()[0].addEventListener("ended", () => this.useBeat());  // user hit "Stop sharing"
    return true;
  }

  useBeat() {
    this._teardownExt();
    for (const [name, g] of Object.entries(this.stemGain)) {
      g.gain.setTargetAtTime(this._mix[name] ?? 1, this.ctx.currentTime, 0.05);
    }
    this.mode = "beat";
  }

  _teardownExt() {
    if (this.extSource) { try { this.extSource.disconnect(); } catch (_) {} this.extSource = null; }
    if (this.extStream) { this.extStream.getTracks().forEach((t) => t.stop()); this.extStream = null; }
  }

  // stutter gate scheduler — chops the dry path into 1/8..1/32 slices while held.
  _tick() {
    if (!this.playing) return;
    const ctx = this.ctx, ahead = ctx.currentTime + 0.12;
    if (this._stutter < 0.18) { this._gateT = ctx.currentTime; this.gate.gain.setTargetAtTime(1, ctx.currentTime, 0.01); return; }
    const slice = (BEAT / 2) * (1 - this._stutter) + (BEAT / 8) * this._stutter; // ~1/8 -> ~1/32
    while (this._gateT < ahead) {
      const t = Math.max(this._gateT, ctx.currentTime);
      this.gate.gain.setValueAtTime(1, t);
      this.gate.gain.exponentialRampToValueAtTime(0.16, t + slice * 0.92);
      this._gateT += slice;
    }
  }
}