05Bass-bouncing letters

<svg width="0" height="0" style="position:absolute" aria-hidden="true">
  <defs>
    <symbol id="ico-waveform" viewBox="0 0 256 256" fill="currentColor"><path d="M208 96v64H48V96Z" opacity=".2"/><path d="M56 96v64a8 8 0 0 1-16 0V96a8 8 0 0 1 16 0m32-72a8 8 0 0 0-8 8v192a8 8 0 0 0 16 0V32a8 8 0 0 0-8-8m40 32a8 8 0 0 0-8 8v128a8 8 0 0 0 16 0V64a8 8 0 0 0-8-8m40 32a8 8 0 0 0-8 8v64a8 8 0 0 0 16 0V96a8 8 0 0 0-8-8m40-16a8 8 0 0 0-8 8v96a8 8 0 0 0 16 0V72a8 8 0 0 0-8-8"/></symbol>
    <symbol id="ico-play" viewBox="0 0 256 256" fill="currentColor"><path d="M228.23 134.69L84.15 222.81A8 8 0 0 1 72 216.12V39.88a8 8 0 0 1 12.15-6.69l144.08 88.12a7.82 7.82 0 0 1 0 13.38" opacity=".2"/><path d="M232.4 114.49L88.32 26.35a16 16 0 0 0-16.2-.3A15.86 15.86 0 0 0 64 39.87v176.26A15.94 15.94 0 0 0 80 232a16.07 16.07 0 0 0 8.36-2.35l144.04-88.14a15.88 15.88 0 0 0 0-27.02M80 215.94V40l143.83 88Z"/></symbol>
    <symbol id="ico-pause" viewBox="0 0 256 256" fill="currentColor"><path d="M208 48v160a8 8 0 0 1-8 8h-40a8 8 0 0 1-8-8V48a8 8 0 0 1 8-8h40a8 8 0 0 1 8 8M96 40H56a8 8 0 0 0-8 8v160a8 8 0 0 0 8 8h40a8 8 0 0 0 8-8V48a8 8 0 0 0-8-8" opacity=".2"/><path d="M200 32h-40a16 16 0 0 0-16 16v160a16 16 0 0 0 16 16h40a16 16 0 0 0 16-16V48a16 16 0 0 0-16-16m0 176h-40V48h40zM96 32H56a16 16 0 0 0-16 16v160a16 16 0 0 0 16 16h40a16 16 0 0 0 16-16V48a16 16 0 0 0-16-16m0 176H56V48h40z"/></symbol>
  </defs>
</svg>
<main class="stage">
<div class="tb is-demo" id="tb">
  <p class="tb__hint"><svg class="tb__ico" aria-hidden="true"><use href="#ico-waveform"/></svg><span>Press play and it moves with real sound</span></p>
  <h2 class="tb__title" aria-label="GODRICH">
    <!-- 글자마다 data-band 로 대역을 나눈다: G·R 는 Bass, O·I·H 는 Mid, D·C 는 Treble. 브랜드 낱말이라 로케일을 안 탄다. -->
    <b class="tb__l" data-band="0">G</b><b class="tb__l" data-band="1">O</b><b class="tb__l" data-band="2">D</b><b class="tb__l" data-band="0">R</b><b class="tb__l" data-band="1">I</b><b class="tb__l" data-band="2">C</b><b class="tb__l" data-band="1">H</b>
  </h2>
  <ul class="tb__legend" aria-hidden="true">
    <li class="tb__band tb__band--low">Bass</li>
    <li class="tb__band tb__band--mid">Mid</li>
    <li class="tb__band tb__band--high">Treble</li>
  </ul>
  <div class="tb__foot">
    <button class="tb__play" id="play" type="button" aria-pressed="false">
      <svg class="tb__ico tb__ico--play" aria-hidden="true"><use href="#ico-play"/></svg>
      <svg class="tb__ico tb__ico--pause" aria-hidden="true"><use href="#ico-pause"/></svg>
      <span id="playLabel">Play</span>
    </button>
    <p class="tb__level">
      <span class="tb__levelLabel">Loudest band</span>
      <b class="tb__levelBox">
        <span class="tb__levelText" id="levelText" aria-live="polite">Bass</span>
        <span class="tb__loop" aria-hidden="true"><i>Bass</i><i>Mid</i><i>Treble</i></span>
      </b>
    </p>
  </div>
</div>
</main>

@use "../../../../site/static/demo-tokens" as *;

// 저음에 튀는 글자 — 제목의 글자를 저·중·고 대역에 나눠 건다. 대역마다 다른 글자가 튄다.
// 글자는 자기 자리에서 커져야 하므로(규칙 8) transform-origin 은 중심 그대로 — translateY 와 scale 만 쓴다.
// --j 는 실제 소리에서 온 대역 에너지(0~1). 재생을 누르면 JS 가 매 프레임 쓴다.

$duration: $dur-quick;
$easing: $ease-pop;
$color: $subject-ink;

@include stage($stage-orange);

.tb { display: flex; flex-direction: column; align-items: center; gap: $sp-3; width: 100%; }
.tb__hint {
  display: flex; align-items: center; gap: $sp-1; margin: 0;
  font-weight: 700; font-size: clamp(11px, 3vw, 12px); color: $subject-ink;
}
.tb__ico { width: 16px; height: 16px; color: $subject-ink; }

.tb__title { margin: 0; display: flex; align-items: baseline; gap: $sp-1; font-weight: 900; }
.tb__l {
  display: inline-block; font-size: clamp(44px, 12vw, 60px); line-height: 1; color: $color;
  transform-origin: 50% 50%;
  transform: translateY(calc(-18px * var(--j, 0))) scale(calc(1 + var(--j, 0) * .16));
  transition: transform $duration $easing;
}

// 대역 범례 — 어떤 글자가 어느 대역에 걸렸는지 색으로 보여준다(소리 없는 독자용 보조)
.tb__legend { margin: 0; padding: 0; list-style: none; display: flex; gap: $sp-1; }
.tb__band {
  border-radius: $r-pill; padding: 0 $sp-2; height: 18px; display: grid; place-items: center;
  font-weight: 800; font-size: clamp(10px, 2.6vw, 11px); line-height: 1; color: $subject-ink;
  border: 2px solid rgba($subject-ink, .5);
}
.tb__band--low::before, .tb__band--mid::before, .tb__band--high::before {
  content: ""; width: 8px; height: 8px; border-radius: 50%; margin-right: $sp-1;
}
.tb__band--low::before { background: #905a47; }
.tb__band--mid::before { background: $subject-ink; }
.tb__band--high::before { background: rgba($subject-ink, .38); }

.tb__foot { display: flex; align-items: center; justify-content: center; gap: $sp-4; width: 100%; }
.tb__play {
  display: inline-flex; align-items: center; gap: $sp-1;
  border: 0; border-radius: $r-pill; padding: $sp-2 $sp-4;
  background: $subject-ink; color: $subject-cream; cursor: pointer;
  font-family: inherit; font-weight: 800; font-size: clamp(11px, 3vw, 12px); line-height: 1;
}
.tb__ico--pause { display: none; }
.tb__play[aria-pressed="true"] .tb__ico--play { display: none; }
.tb__play[aria-pressed="true"] .tb__ico--pause { display: inline-block; }
.tb__play .tb__ico { color: $subject-cream; }

.tb__level { margin: 0; display: flex; align-items: center; gap: $sp-2; }
.tb__levelLabel { font-weight: 700; font-size: clamp(10px, 2.6vw, 11px); color: $subject-ink; }
// 주황 무대 위 작은 글자 — 반투명 크림판을 깔아 밝힌 뒤 잉크 글자로 (잉크/주황 직접 조합은 4.5:1 에 아슬)
.tb__levelBox {
  position: relative; display: grid; place-items: center;
  min-width: 40px; height: 20px; border-radius: $r-xs; padding: 0 $sp-1;
  background: rgba($subject-cream, .3); color: $subject-ink;
  font-weight: 800; font-size: clamp(11px, 3vw, 12px); line-height: 1;
}
.tb__loop { position: absolute; inset: 0; display: grid; place-items: center; visibility: hidden; }
.tb__loop i { grid-area: 1 / 1; font-style: normal; visibility: hidden; }

// ── 격자 미리보기 루프 ─────────────────────────────────────────────
// 여섯 글자가 160ms 간격으로 차례로 튄다(양수 지연 + backwards — 지연 구간엔 0% 정지 자세가 유지된다).
// 글자는 크지만 색상은 그대로고 위치 이동만 있어 밝기 반전은 없다 — 광과민성 한계와 무관하다.
.tb.is-demo .tb__l {
  animation-name: tbJump; animation-duration: $dur-loop; animation-timing-function: $easing;
  animation-iteration-count: infinite; animation-fill-mode: backwards;
  animation-delay: calc(var(--n) * 140ms);
  transition: none;
}
// 순서값 --n — 일곱 글자가 왼쪽부터 140ms 간격으로 도는 파도가 된다(7 × 140ms = 980ms < 2s)
.tb.is-demo .tb__l:nth-child(1) { --n: 0; }
.tb.is-demo .tb__l:nth-child(2) { --n: 1; }
.tb.is-demo .tb__l:nth-child(3) { --n: 2; }
.tb.is-demo .tb__l:nth-child(4) { --n: 3; }
.tb.is-demo .tb__l:nth-child(5) { --n: 4; }
.tb.is-demo .tb__l:nth-child(6) { --n: 5; }
.tb.is-demo .tb__l:nth-child(7) { --n: 6; }
@keyframes tbJump {
  0%, 8%   { transform: translateY(0) scale(1); }
  16%, 30% { transform: translateY(-18px) scale(1.16); }
  44%, 100% { transform: translateY(0) scale(1); }
}
.tb.is-demo .tb__levelText { color: transparent; }
.tb.is-demo .tb__loop { visibility: visible; }
.tb.is-demo .tb__loop i {
  animation-name: tbBandName; animation-duration: $dur-loop; animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}
.tb.is-demo .tb__loop i:nth-child(1) { animation-delay: 0ms; }
.tb.is-demo .tb__loop i:nth-child(2) { animation-delay: 666ms; }
.tb.is-demo .tb__loop i:nth-child(3) { animation-delay: 1332ms; }
@keyframes tbBandName {
  0%, 33% { visibility: visible; }
  34%, 100% { visibility: hidden; }
}

@media (max-width: 340px) {
  .tb { gap: $sp-1; }
  .tb__l { font-size: 34px; }
  .tb__foot { gap: $sp-2; }
  .tb__play { padding: $sp-1 $sp-3; }
}

// reduce 에서는 루프를 끈다 — 글자는 제자리에 그대로 보이고, 범례가 대역 구분을 대신 설명한다
@media (prefers-reduced-motion: reduce) {
  .tb.is-demo .tb__l,
  .tb.is-demo .tb__loop i { animation: none !important; }
  .tb.is-demo .tb__levelText { color: $subject-ink !important; }
  .tb.is-demo .tb__loop { visibility: hidden !important; }
  .tb__l { transition: none !important; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ff4d1f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.tb {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 12px;
  width: 100%;
}

.tb__hint {
  display: flex;
  align-items: center;
  gap: 4px;
  margin: 0;
  font-weight: 700;
  font-size: clamp(11px, 3vw, 12px);
  color: #17141a;
}

.tb__ico {
  width: 16px;
  height: 16px;
  color: #17141a;
}

.tb__title {
  margin: 0;
  display: flex;
  align-items: baseline;
  gap: 4px;
  font-weight: 900;
}

.tb__l {
  display: inline-block;
  font-size: clamp(44px, 12vw, 60px);
  line-height: 1;
  color: #17141a;
  transform-origin: 50% 50%;
  transform: translateY(calc(-18px * var(--j, 0))) scale(calc(1 + var(--j, 0) * 0.16));
  transition: transform 220ms cubic-bezier(0.2, 1.4, 0.4, 1);
}

.tb__legend {
  margin: 0;
  padding: 0;
  list-style: none;
  display: flex;
  gap: 4px;
}

.tb__band {
  border-radius: 999px;
  padding: 0 8px;
  height: 18px;
  display: grid;
  place-items: center;
  font-weight: 800;
  font-size: clamp(10px, 2.6vw, 11px);
  line-height: 1;
  color: #17141a;
  border: 2px solid rgba(23, 20, 26, 0.5);
}

.tb__band--low::before, .tb__band--mid::before, .tb__band--high::before {
  content: "";
  width: 8px;
  height: 8px;
  border-radius: 50%;
  margin-right: 4px;
}

.tb__band--low::before {
  background: #905a47;
}

.tb__band--mid::before {
  background: #17141a;
}

.tb__band--high::before {
  background: rgba(23, 20, 26, 0.38);
}

.tb__foot {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 16px;
  width: 100%;
}

.tb__play {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  border: 0;
  border-radius: 999px;
  padding: 8px 16px;
  background: #17141a;
  color: #fff7e6;
  cursor: pointer;
  font-family: inherit;
  font-weight: 800;
  font-size: clamp(11px, 3vw, 12px);
  line-height: 1;
}

.tb__ico--pause {
  display: none;
}

.tb__play[aria-pressed=true] .tb__ico--play {
  display: none;
}

.tb__play[aria-pressed=true] .tb__ico--pause {
  display: inline-block;
}

.tb__play .tb__ico {
  color: #fff7e6;
}

.tb__level {
  margin: 0;
  display: flex;
  align-items: center;
  gap: 8px;
}

.tb__levelLabel {
  font-weight: 700;
  font-size: clamp(10px, 2.6vw, 11px);
  color: #17141a;
}

.tb__levelBox {
  position: relative;
  display: grid;
  place-items: center;
  min-width: 40px;
  height: 20px;
  border-radius: 4px;
  padding: 0 4px;
  background: rgba(255, 247, 230, 0.3);
  color: #17141a;
  font-weight: 800;
  font-size: clamp(11px, 3vw, 12px);
  line-height: 1;
}

.tb__loop {
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
  visibility: hidden;
}

.tb__loop i {
  grid-area: 1/1;
  font-style: normal;
  visibility: hidden;
}

.tb.is-demo .tb__l {
  animation-name: tbJump;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 1.4, 0.4, 1);
  animation-iteration-count: infinite;
  animation-fill-mode: backwards;
  animation-delay: calc(var(--n) * 140ms);
  transition: none;
}

.tb.is-demo .tb__l:nth-child(1) {
  --n: 0;
}

.tb.is-demo .tb__l:nth-child(2) {
  --n: 1;
}

.tb.is-demo .tb__l:nth-child(3) {
  --n: 2;
}

.tb.is-demo .tb__l:nth-child(4) {
  --n: 3;
}

.tb.is-demo .tb__l:nth-child(5) {
  --n: 4;
}

.tb.is-demo .tb__l:nth-child(6) {
  --n: 5;
}

.tb.is-demo .tb__l:nth-child(7) {
  --n: 6;
}

@keyframes tbJump {
  0%, 8% {
    transform: translateY(0) scale(1);
  }
  16%, 30% {
    transform: translateY(-18px) scale(1.16);
  }
  44%, 100% {
    transform: translateY(0) scale(1);
  }
}
.tb.is-demo .tb__levelText {
  color: transparent;
}

.tb.is-demo .tb__loop {
  visibility: visible;
}

.tb.is-demo .tb__loop i {
  animation-name: tbBandName;
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}

.tb.is-demo .tb__loop i:nth-child(1) {
  animation-delay: 0ms;
}

.tb.is-demo .tb__loop i:nth-child(2) {
  animation-delay: 666ms;
}

.tb.is-demo .tb__loop i:nth-child(3) {
  animation-delay: 1332ms;
}

@keyframes tbBandName {
  0%, 33% {
    visibility: visible;
  }
  34%, 100% {
    visibility: hidden;
  }
}
@media (max-width: 340px) {
  .tb {
    gap: 4px;
  }
  .tb__l {
    font-size: 34px;
  }
  .tb__foot {
    gap: 8px;
  }
  .tb__play {
    padding: 4px 12px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .tb.is-demo .tb__l,
  .tb.is-demo .tb__loop i {
    animation: none !important;
  }
  .tb.is-demo .tb__levelText {
    color: #17141a !important;
  }
  .tb.is-demo .tb__loop {
    visibility: hidden !important;
  }
  .tb__l {
    transition: none !important;
  }
}

var root = document.getElementById('tb');
var playBtn = document.getElementById('play');
var playLabel = document.getElementById('playLabel');
var levelText = document.getElementById('levelText');
var letters = Array.prototype.slice.call(document.querySelectorAll('.tb__l'));
var ctx = null, analyser = null, freq = null, timer = 0, playing = false;
var BAND_NAMES = ['Bass', 'Mid', 'Treble'];
function buildAudio() {
  ctx = new (window.AudioContext || window.webkitAudioContext)();
  analyser = ctx.createAnalyser();
  analyser.fftSize = 64;
  analyser.smoothingTimeConstant = 0.6;
  freq = new Uint8Array(analyser.frequencyBinCount);
  var out = ctx.createGain();
  out.gain.value = 0.06;
  out.connect(analyser);
  analyser.connect(ctx.destination);
  // 외부 음원 파일 없이 코드 진행을 직접 합성한다 — 네 박자마다 화음이 바뀐다.
  [196, 246.94, 293.66, 392].forEach(function (hz, n) {
    var osc = ctx.createOscillator();
    var amp = ctx.createGain();
    osc.type = n === 3 ? 'triangle' : 'sawtooth';
    osc.frequency.value = hz;
    amp.gain.value = 0;
    for (var beat = 0; beat < 64; beat++) {
      var at = ctx.currentTime + beat * 0.5;
      amp.gain.setValueAtTime(beat % 4 === n % 4 ? 0.9 : 0.25, at);
      amp.gain.exponentialRampToValueAtTime(0.02, at + 0.45);
    }
    osc.connect(amp); amp.connect(out); osc.start();
  });
}
function draw() {
  analyser.getByteFrequencyData(freq);
  // 대역 세 개의 에너지를 0~1 로 만들어 글자의 --j 로 넣는다. 대역마다 다른 글자가 튄다.
  // 경계는 Bass 1~2번 빈, Mid 3~5번, Treble 6~10번 — 톱니파 고조파는 1/n 으로 줄어 성김문제로
  // 중·고음에는 표시 게인(1.5·2.2배)을 준다. 미터 눈금 보정이지 소리를 키우는 게 아니다.
  var GAIN = [1, 1.5, 2.2];
  var bands = [0, 0, 0];
  for (var k = 1; k <= 10; k++) {
    var b = k <= 2 ? 0 : k <= 5 ? 1 : 2;
    bands[b] += freq[k] / 255 / (b === 0 ? 2 : b === 1 ? 3 : 5);
  }
  for (var j = 0; j < 3; j++) { bands[j] = Math.min(1, bands[j] * GAIN[j]); }
  for (var i = 0; i < letters.length; i++) {
    var b = Number(letters[i].getAttribute('data-band'));
    letters[i].style.setProperty('--j', bands[b].toFixed(3));
  }
  var top = bands.indexOf(Math.max(bands[0], bands[1], bands[2]));
  if (levelText.textContent !== BAND_NAMES[top]) { levelText.textContent = BAND_NAMES[top]; }
  timer = requestAnimationFrame(draw);
}
playBtn.addEventListener('click', function () {
  root.classList.remove('is-demo');
  if (!ctx) { buildAudio(); }
  playing = !playing;
  playBtn.setAttribute('aria-pressed', playing ? 'true' : 'false');
  playLabel.textContent = playing ? 'Stop' : 'Play';
  // 자동재생 정책: AudioContext 는 사용자 제스처 뒤 resume() 해야 소리가 난다.
  if (playing) { ctx.resume(); timer = requestAnimationFrame(draw); }
  else { ctx.suspend(); cancelAnimationFrame(timer); }
});

// TextBounce — vanilla 판(run/291/demo/05-audio-viz-text-bounce/index.html) 의 React 포트.
// 제목의 글자를 저·중·고 대역에 나눠 건다. 대역마다 다른 글자가 튄다(글자는 자기 중심에서 커진다).
import { useEffect, useRef, useState } from "react";
import type { CSSProperties } from "react";
import styles from "./TextBounce.module.scss";

export type TextBounceProps = {
  /** 격자 미리보기용 2초 자동 루프. 재생을 누르면 꺼진다 */
  demo?: boolean;
  duration?: number;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
type LetterVars = CSSProperties & { "--j"?: string };
/** ambient 타입에 useRef<T> 의 null 합집합이 없어 로컬로 좁힌다 */
type Box<T> = { current: T };

const BAND_NAMES = ["저음", "중음", "고음"];
/** 브랜드 낱말이라 로케일을 안 탄다. data-band 로 저·중·고에 나눠 건다 */
const LETTERS: { ch: string; band: number }[] = [
  { ch: "G", band: 0 },
  { ch: "O", band: 1 },
  { ch: "D", band: 2 },
  { ch: "R", band: 0 },
  { ch: "I", band: 1 },
  { ch: "C", band: 2 },
  { ch: "H", band: 1 },
];

export default function TextBounce({
  demo = true,
  duration = 220,
  easing = "cubic-bezier(.2, 1.4, .4, 1)",
  color = "#17141a",
}: TextBounceProps) {
  const [live, setLive] = useState(demo);
  const [playing, setPlaying] = useState(false);
  const [bands, setBands] = useState<number[]>([0, 0, 0]);
  const ctxBox = useRef(null) as Box<AudioContext | null>;
  const nodeBox = useRef(null) as Box<AnalyserNode | null>;
  const frameBox = useRef(0) as Box<number>;
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  useEffect(() => {
    return () => {
      cancelAnimationFrame(frameBox.current);
      if (ctxBox.current) {
        ctxBox.current.close();
      }
    };
  }, []);

  function buildAudio() {
    const ctx = new AudioContext();
    const analyser = ctx.createAnalyser();
    analyser.fftSize = 64;
    analyser.smoothingTimeConstant = 0.6;
    const out = ctx.createGain();
    out.gain.value = 0.06;
    out.connect(analyser);
    analyser.connect(ctx.destination);
    // 외부 음원 파일 없이 코드 진행을 직접 합성한다 — 네 박자마다 화음이 바뀐다.
    [196, 246.94, 293.66, 392].forEach((hz, n) => {
      const osc = ctx.createOscillator();
      const amp = ctx.createGain();
      osc.type = n === 3 ? "triangle" : "sawtooth";
      osc.frequency.value = hz;
      amp.gain.value = 0;
      for (let beat = 0; beat < 64; beat++) {
        const at = ctx.currentTime + beat * 0.5;
        amp.gain.setValueAtTime(beat % 4 === n % 4 ? 0.9 : 0.25, at);
        amp.gain.exponentialRampToValueAtTime(0.02, at + 0.45);
      }
      osc.connect(amp);
      amp.connect(out);
      osc.start();
    });
    ctxBox.current = ctx;
    nodeBox.current = analyser;
  }

  function draw() {
    const analyser = nodeBox.current;
    if (!analyser) {
      return;
    }
    const freq = new Uint8Array(analyser.frequencyBinCount);
    analyser.getByteFrequencyData(freq);
    // 대역 세 개의 에너지를 0~1 로 만들어 글자의 --j 로 넣는다(중·고음 게인 보정은 vanilla 주석 참조).
    const GAIN = [1, 1.5, 2.2];
    const next = [0, 0, 0];
    for (let k = 1; k <= 10; k++) {
      const b = k <= 2 ? 0 : k <= 5 ? 1 : 2;
      next[b] += freq[k] / 255 / (b === 0 ? 2 : b === 1 ? 3 : 5);
    }
    for (let j = 0; j < 3; j++) {
      next[j] = Math.min(1, next[j] * GAIN[j]);
    }
    setBands(next);
    frameBox.current = requestAnimationFrame(draw);
  }

  function toggle() {
    setLive(false);
    if (!ctxBox.current) {
      buildAudio();
    }
    const ctx = ctxBox.current;
    if (!ctx) {
      return;
    }
    const next = !playing;
    setPlaying(next);
    // 자동재생 정책: AudioContext 는 사용자 제스처 뒤 resume() 해야 소리가 난다.
    if (next) {
      ctx.resume();
      frameBox.current = requestAnimationFrame(draw);
    } else {
      ctx.suspend();
      cancelAnimationFrame(frameBox.current);
    }
  }

  const cls = [styles.root, live ? styles.isDemo : ""].filter(Boolean).join(" ");
  const top = bands.indexOf(Math.max(bands[0], bands[1], bands[2]));
  return (
    <main className={styles.stage} style={vars}>
      <svg width="0" height="0" style={{ position: "absolute" }} aria-hidden="true">
        <defs>
          <symbol id="ico-waveform" viewBox="0 0 256 256" fill="currentColor">
            <path d="M208 96v64H48V96Z" opacity=".2" />
            <path d="M56 96v64a8 8 0 0 1-16 0V96a8 8 0 0 1 16 0m32-72a8 8 0 0 0-8 8v192a8 8 0 0 0 16 0V32a8 8 0 0 0-8-8m40 32a8 8 0 0 0-8 8v128a8 8 0 0 0 16 0V64a8 8 0 0 0-8-8m40 32a8 8 0 0 0-8 8v64a8 8 0 0 0 16 0V96a8 8 0 0 0-8-8m40-16a8 8 0 0 0-8 8v96a8 8 0 0 0 16 0V72a8 8 0 0 0-8-8" />
          </symbol>
          <symbol id="ico-play" viewBox="0 0 256 256" fill="currentColor">
            <path d="M228.23 134.69L84.15 222.81A8 8 0 0 1 72 216.12V39.88a8 8 0 0 1 12.15-6.69l144.08 88.12a7.82 7.82 0 0 1 0 13.38" opacity=".2" />
            <path d="M232.4 114.49L88.32 26.35a16 16 0 0 0-16.2-.3A15.86 15.86 0 0 0 64 39.87v176.26A15.94 15.94 0 0 0 80 232a16.07 16.07 0 0 0 8.36-2.35l144.04-88.14a15.88 15.88 0 0 0 0-27.02M80 215.94V40l143.83 88Z" />
          </symbol>
          <symbol id="ico-pause" viewBox="0 0 256 256" fill="currentColor">
            <path d="M208 48v160a8 8 0 0 1-8 8h-40a8 8 0 0 1-8-8V48a8 8 0 0 1 8-8h40a8 8 0 0 1 8 8M96 40H56a8 8 0 0 0-8 8v160a8 8 0 0 0 8 8h40a8 8 0 0 0 8-8V48a8 8 0 0 0-8-8" opacity=".2" />
            <path d="M200 32h-40a16 16 0 0 0-16 16v160a16 16 0 0 0 16 16h40a16 16 0 0 0 16-16V48a16 16 0 0 0-16-16m0 176h-40V48h40zM96 32H56a16 16 0 0 0-16 16v160a16 16 0 0 0 16 16h40a16 16 0 0 0 16-16V48a16 16 0 0 0-16-16m0 176H56V48h40z" />
          </symbol>
        </defs>
      </svg>
      <div className={cls}>
        <p className={styles.hint}>
          <svg className={styles.ico} aria-hidden="true">
            <use href="#ico-waveform" />
          </svg>
          <span>재생을 누르면 실제 소리로 움직입니다</span>
        </p>
        <h2 className={styles.title} aria-label="GODRICH">
          {LETTERS.map((l, i) => {
            const letterVars: LetterVars = { "--j": bands[l.band].toFixed(3) };
            return (
              <b className={styles.l} key={i} style={letterVars}>
                {l.ch}
              </b>
            );
          })}
        </h2>
        <ul className={styles.legend} aria-hidden="true">
          <li className={styles.bandLow}>저음</li>
          <li className={styles.bandMid}>중음</li>
          <li className={styles.bandHigh}>고음</li>
        </ul>
        <div className={styles.foot}>
          <button className={styles.play} type="button" aria-pressed={playing} onClick={toggle}>
            <svg className={[styles.ico, playing ? styles.icoHidden : ""].join(" ")} aria-hidden="true">
              <use href="#ico-play" />
            </svg>
            <svg className={[styles.ico, playing ? "" : styles.icoHidden].join(" ")} aria-hidden="true">
              <use href="#ico-pause" />
            </svg>
            <span>{playing ? "정지" : "재생"}</span>
          </button>
          <p className={styles.level}>
            <span className={styles.levelLabel}>센 대역</span>
            <b className={styles.levelBox}>
              <span className={styles.levelText} aria-live="polite">
                {BAND_NAMES[top]}
              </span>
              <span className={styles.loop} aria-hidden="true">
                <i>저음</i>
                <i>중음</i>
                <i>고음</i>
              </span>
            </b>
          </p>
        </div>
      </div>
    </main>
  );
}