06十六の振り子が扇形に広がる色の帯

<main class="stage">
<div class="bp is-demo" id="bpRoot">
  <canvas class="bp__canvas" id="bpCanvas" width="480" height="300" tabindex="0" aria-label="出発角度を番号に比例して少しずつ広げた十六の振り子を色相順に重ねて描き、一点から出た虹がある瞬間に散らばって絡まる場面を見せる。"></canvas>
  <p class="bp__status" id="bpStatus" aria-live="polite">デモ実行中</p>
  <button class="bp__btn" id="bpBtn" type="button">一時停止</button>
  <p class="bp__caption">出発角度を番号に比例して少しずつ広げた十六の振り子を色相順に重ねて描き、一点から出た虹がある瞬間に散らばって絡まる場面を見せる。</p>
</div>
</main>

@use "../../../../site/static/demo-tokens" as *;
@include stage($stage-ink);

.bp {
  position: relative;
  width: min(92vw, calc(160vh - 12.8vw));
  aspect-ratio: 480 / 300;
  margin: 0 auto;
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
  background: $stage-ink;
}

.bp__canvas {
  display: block;
  width: 100%;
  height: 100%;
  touch-action: none;
}

.bp__canvas:focus-visible {
  outline: 2px solid rgba(255, 255, 255, .85);
  outline-offset: -6px;
}

.bp__status {
  position: absolute;
  left: $sp-3;
  top: $sp-3;
  max-width: 70%;
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(255, 255, 255, .85);
  color: $subject-ink;
  font-weight: 500;
  font-size: 11px;
  line-height: 1.4;
  pointer-events: none;
}

.bp__btn {
  position: absolute;
  right: $sp-3;
  bottom: $sp-3;
  margin: 0;
  padding: $sp-1 $sp-3;
  border: 0;
  border-radius: $r-pill;
  background: rgba(255, 255, 255, .85);
  color: $subject-ink;
  font: inherit;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  cursor: pointer;
}

.bp__btn:focus-visible {
  outline: 2px solid #ffffff;
  outline-offset: 2px;
}

.bp__caption {
  position: absolute;
  left: $sp-3;
  bottom: $sp-3;
  max-width: 68%;
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(255, 255, 255, .85);
  color: $subject-ink;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

@media (max-width: 340px) {
  .bp__caption, .bp__btn { font-size: 10px; padding: $sp-1 $sp-2; }
  .bp__status { font-size: 10px; }
}

@media (prefers-reduced-motion: reduce) {
  .bp { cursor: default; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.bp {
  position: relative;
  width: min(92vw, 160vh - 12.8vw);
  aspect-ratio: 480/300;
  margin: 0 auto;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  background: #17141a;
}

.bp__canvas {
  display: block;
  width: 100%;
  height: 100%;
  touch-action: none;
}

.bp__canvas:focus-visible {
  outline: 2px solid rgba(255, 255, 255, 0.85);
  outline-offset: -6px;
}

.bp__status {
  position: absolute;
  left: 12px;
  top: 12px;
  max-width: 70%;
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.85);
  color: #17141a;
  font-weight: 500;
  font-size: 11px;
  line-height: 1.4;
  pointer-events: none;
}

.bp__btn {
  position: absolute;
  right: 12px;
  bottom: 12px;
  margin: 0;
  padding: 4px 12px;
  border: 0;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.85);
  color: #17141a;
  font: inherit;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  cursor: pointer;
}

.bp__btn:focus-visible {
  outline: 2px solid #ffffff;
  outline-offset: 2px;
}

.bp__caption {
  position: absolute;
  left: 12px;
  bottom: 12px;
  max-width: 68%;
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.85);
  color: #17141a;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

@media (max-width: 340px) {
  .bp__caption, .bp__btn {
    font-size: 10px;
    padding: 4px 8px;
  }
  .bp__status {
    font-size: 10px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .bp {
    cursor: default;
  }
}

(function () {
  var root = document.getElementById('bpRoot');
  var canvas = document.getElementById('bpCanvas');
  var statusEl = document.getElementById('bpStatus');
  var btnEl = document.getElementById('bpBtn');
  "use strict";
  function main(root, canvas, statusEl, btnEl) {
      var ctx0 = canvas.getContext('2d');
      if (!ctx0) {
          return function () { return; };
      }
      var ctx = ctx0;
      var wrap = canvas.parentElement ? canvas.parentElement : root;
      var CALC_W = 320, CALC_H = 200;
      var FIXED_DT = 16;
      var REDUCE_STEP_FRAMES = 40;
      var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
      var demo = !reduce;
      if (!demo)
          root.classList.remove('is-demo');
      function stopDemo() { demo = false; root.classList.remove('is-demo'); }
      var paused = false;
      var ownInput = false;
      var cw = 480, ch = 300, sc = 1.5, elapsed = 0, rafId = 0;
      var cleaners = [];
      function listen(target, type, fn) {
          target.addEventListener(type, fn);
          cleaners.push(function () { target.removeEventListener(type, fn); });
      }
      function clamp(v, lo, hi) { return v < lo ? lo : (v > hi ? hi : v); }
      function setStatus(msg) { statusEl.textContent = msg; }
      function hsl(h, s, l, a) {
          return 'hsla(' + (h % 360) + ',' + s + '%,' + l + '%,' + a + ')';
      }
      function canvasPoint(e) {
          var r = canvas.getBoundingClientRect();
          return { x: (e.clientX - r.left) / r.width * CALC_W, y: (e.clientY - r.top) / r.height * CALC_H };
      }
      // 배경 — 어두운 잉크색 위에 방사형 빛무리를 (gx, gy) 에 깐다
      function beginDraw(inner, outer, gx, gy) {
          ctx.setTransform(1, 0, 0, 1, 0, 0);
          ctx.fillStyle = '#1d1a2b';
          ctx.fillRect(0, 0, cw, ch);
          ctx.setTransform(sc, 0, 0, sc, 0, 0);
          var g = ctx.createRadialGradient(gx, gy, 8, gx, gy, 230);
          g.addColorStop(0, inner);
          g.addColorStop(1, outer);
          ctx.fillStyle = g;
          ctx.fillRect(0, 0, CALC_W, CALC_H);
      }
      function seg(x1, y1, x2, y2, w, col) {
          ctx.beginPath();
          ctx.moveTo(x1, y1);
          ctx.lineTo(x2, y2);
          ctx.lineCap = 'round';
          ctx.lineWidth = w;
          ctx.strokeStyle = col;
          ctx.stroke();
      }
      function disc(x, y, r, col) {
          ctx.beginPath();
          ctx.arc(x, y, r, 0, 6.2832);
          ctx.fillStyle = col;
          ctx.fill();
      }
      function glow(x, y, r, rgb, a) {
          var g = ctx.createRadialGradient(x, y, 0, x, y, r);
          g.addColorStop(0, 'rgba(' + rgb + ',' + a + ')');
          g.addColorStop(1, 'rgba(' + rgb + ',0)');
          ctx.fillStyle = g;
          ctx.fillRect(x - r, y - r, r * 2, r * 2);
      }
      function drawTrail(arr, rgb, w, alpha) {
          ctx.lineCap = 'round';
          for (var i = 1; i < arr.length; i += 1) {
              var f = i / arr.length;
              ctx.beginPath();
              ctx.moveTo(arr[i - 1].x, arr[i - 1].y);
              ctx.lineTo(arr[i].x, arr[i].y);
              ctx.strokeStyle = 'rgba(' + rgb + ',' + (alpha * f * f) + ')';
              ctx.lineWidth = w * (0.3 + 0.7 * f);
              ctx.stroke();
          }
      }
      function pushTrail(arr, x, y, max) {
          arr.push({ x: x, y: y });
          if (arr.length > max) {
              arr.shift();
          }
      }
      function defaultToggle() {
          if (reduce) {
              for (var i = 0; i < REDUCE_STEP_FRAMES; i += 1) {
                  elapsed += FIXED_DT;
                  stepFrame();
              }
              draw();
              setStatus('一場面ずつ送っています');
              return;
          }
          paused = !paused;
          btnEl.textContent = paused ? '再生' : '一時停止';
          setStatus(paused ? '一時停止中' : 'デモ実行中');
      }
      var onButton = defaultToggle;
      // 기법: 출발 각도를 OFFSET_STEP 에 번호를 곱한 식으로만 벌려 열여섯 진자를 한 식으로 적분하고, 번호를 색상에 그대로 대응시킨다
      var DT = 0.01;
      var SUBSTEPS = 3;
      var START_T1 = 2.4;
      var START_T2 = 2.2;
      var COUNT = 16;
      var OFFSET_STEP = 0.004;
      var HUE_SPAN = 300;
      var SIM_RESET_FRAMES = 340;
      var TRAIL_LEN = 26;
      var L1 = 1.0;
      var L2 = 1.0;
      var M1 = 1.0;
      var M2 = 1.0;
      var G = 9.81;
      var UNIT = 40, PIVOT_X = 160, PIVOT_Y = 74;
      var PREROLL_FRAMES = 40;
      // 라그랑주 운동방정식 — 각도는 아래 방향이 0, 시계 방향이 양수
      function accTheta1(t1, t2, w1, w2) {
          var d = t1 - t2;
          var den = L1 * (2 * M1 + M2 - M2 * Math.cos(2 * d));
          return (-G * (2 * M1 + M2) * Math.sin(t1) - M2 * G * Math.sin(t1 - 2 * t2)
              - 2 * Math.sin(d) * M2 * (w2 * w2 * L2 + w1 * w1 * L1 * Math.cos(d))) / den;
      }
      function accTheta2(t1, t2, w1, w2) {
          var d = t1 - t2;
          var den = L2 * (2 * M1 + M2 - M2 * Math.cos(2 * d));
          return (2 * Math.sin(d) * (w1 * w1 * L1 * (M1 + M2) + G * (M1 + M2) * Math.cos(t1)
              + w2 * w2 * L2 * M2 * Math.cos(d))) / den;
      }
      // 룽게-쿠타 4단계 — 한 걸음을 네 번 기울기로 평균 낸다 (s = [t1, t2, w1, w2])
      function rk4Step(s, h) {
          var t1 = s[0], t2 = s[1], w1 = s[2], w2 = s[3];
          var h2 = h * 0.5;
          var k1a = w1, k1b = w2, k1c = accTheta1(t1, t2, w1, w2), k1d = accTheta2(t1, t2, w1, w2);
          var u1 = t1 + h2 * k1a, u2 = t2 + h2 * k1b, u3 = w1 + h2 * k1c, u4 = w2 + h2 * k1d;
          var k2a = u3, k2b = u4, k2c = accTheta1(u1, u2, u3, u4), k2d = accTheta2(u1, u2, u3, u4);
          u1 = t1 + h2 * k2a;
          u2 = t2 + h2 * k2b;
          u3 = w1 + h2 * k2c;
          u4 = w2 + h2 * k2d;
          var k3a = u3, k3b = u4, k3c = accTheta1(u1, u2, u3, u4), k3d = accTheta2(u1, u2, u3, u4);
          u1 = t1 + h * k3a;
          u2 = t2 + h * k3b;
          u3 = w1 + h * k3c;
          u4 = w2 + h * k3d;
          var k4a = u3, k4b = u4, k4c = accTheta1(u1, u2, u3, u4), k4d = accTheta2(u1, u2, u3, u4);
          s[0] = t1 + h / 6 * (k1a + 2 * k2a + 2 * k3a + k4a);
          s[1] = t2 + h / 6 * (k1b + 2 * k2b + 2 * k3b + k4b);
          s[2] = w1 + h / 6 * (k1c + 2 * k2c + 2 * k3c + k4c);
          s[3] = w2 + h / 6 * (k1d + 2 * k2d + 2 * k3d + k4d);
      }
      function bobOne(s, ox, oy) {
          return { x: ox + UNIT * L1 * Math.sin(s[0]), y: oy + UNIT * L1 * Math.cos(s[0]) };
      }
      function bobTwo(s, ox, oy) {
          var a = bobOne(s, ox, oy);
          return { x: a.x + UNIT * L2 * Math.sin(s[1]), y: a.y + UNIT * L2 * Math.cos(s[1]) };
      }
      function drawArms(s, ox, oy, c1, c2, w) {
          var a = bobOne(s, ox, oy), b = bobTwo(s, ox, oy);
          seg(ox, oy, a.x, a.y, w, c1);
          seg(a.x, a.y, b.x, b.y, w, c2);
      }
      var fan = [];
      var trails = [];
      var frameCount = 0;
      function restart() {
          fan = [];
          trails = [];
          for (var i = 0; i < COUNT; i += 1) {
              fan.push([START_T1 + OFFSET_STEP * i, START_T2, 0, 0]);
              trails.push([]);
          }
          frameCount = 0;
      }
      restart();
      function stepFrame() {
          for (var i = 0; i < COUNT; i += 1) {
              for (var k = 0; k < SUBSTEPS; k += 1) {
                  rk4Step(fan[i], DT);
              }
              var p = bobTwo(fan[i], PIVOT_X, PIVOT_Y);
              pushTrail(trails[i], p.x, p.y, TRAIL_LEN);
          }
          frameCount += 1;
          if (frameCount >= SIM_RESET_FRAMES) {
              restart();
          }
      }
      function hueOf(i) { return 330 + HUE_SPAN * i / (COUNT - 1); }
      function draw() {
          var lead = bobTwo(fan[COUNT >> 1], PIVOT_X, PIVOT_Y);
          beginDraw('#463e68', '#28223f', lead.x, lead.y);
          glow(lead.x, lead.y, 100, '255,238,252', 0.22);
          for (var i = 0; i < COUNT; i += 1) {
              var col = hsl(hueOf(i), 85, 80, 1);
              var p = bobTwo(fan[i], PIVOT_X, PIVOT_Y);
              drawTrail(trails[i], '255,255,255', 2.2, 0.25);
              ctx.lineCap = 'round';
              for (var j = 1; j < trails[i].length; j += 1) {
                  var f = j / trails[i].length;
                  ctx.beginPath();
                  ctx.moveTo(trails[i][j - 1].x, trails[i][j - 1].y);
                  ctx.lineTo(trails[i][j].x, trails[i][j].y);
                  ctx.strokeStyle = hsl(hueOf(i), 85, 80, 0.6 * f);
                  ctx.lineWidth = 1 + 1.6 * f;
                  ctx.stroke();
              }
              drawArms(fan[i], PIVOT_X, PIVOT_Y, hsl(hueOf(i), 80, 82, 0.5), hsl(hueOf(i), 80, 82, 0.7), 1.4);
              glow(p.x, p.y, 10, '255,255,255', 0.35);
              disc(p.x, p.y, 3.2, col);
          }
          disc(PIVOT_X, PIVOT_Y, 4.5, '#fff1c9');
      }
      function fit() {
          var r = wrap.getBoundingClientRect();
          cw = Math.max(1, Math.round(r.width));
          ch = Math.max(1, Math.round(r.height));
          canvas.width = cw;
          canvas.height = ch;
          sc = cw / CALC_W;
          draw();
      }
      var lastTs = null;
      var accMs = 0;
      function tick(ts) {
          if (lastTs === null) {
              lastTs = ts;
          }
          var frameDt = Math.min(ts - lastTs, 48);
          lastTs = ts;
          if (!paused) {
              accMs += frameDt;
              while (accMs >= FIXED_DT) {
                  elapsed += FIXED_DT;
                  stepFrame();
                  accMs -= FIXED_DT;
              }
          }
          draw();
          rafId = requestAnimationFrame(tick);
      }
      for (var w0 = 0; w0 < PREROLL_FRAMES; w0 += 1) {
          elapsed += FIXED_DT;
          stepFrame();
      }
      fit();
      listen(window, 'resize', fit);
      listen(btnEl, 'click', function () { onButton(); });
      if (!ownInput) {
          listen(canvas, 'pointerdown', function () { onButton(); });
          listen(canvas, 'keydown', function (e) {
              var k = e.key;
              if (k === 'Enter' || k === ' ') {
                  e.preventDefault();
                  onButton();
              }
          });
      }
      if (reduce) {
          if (!ownInput) {
              btnEl.textContent = '次の場面';
              setStatus('一場面ずつ送っています');
          }
      }
      else {
          rafId = requestAnimationFrame(tick);
      }
      function destroy() {
          cancelAnimationFrame(rafId);
          for (var i = 0; i < cleaners.length; i += 1) {
              cleaners[i]();
          }
      }
      return destroy;
  }
  main(root, canvas, statusEl, btnEl);
})();

import { useEffect, useRef } from "react";
import styles from "./DpSixteenFanEnsembleHueSpread.module.scss";

function main(root: HTMLDivElement, canvas: HTMLCanvasElement, statusEl: HTMLElement, btnEl: HTMLButtonElement): () => void {
  type Pt = { x: number; y: number };
  var ctx0 = canvas.getContext('2d');
  if (!ctx0) { return function (): void { return; }; }
  var ctx: CanvasRenderingContext2D = ctx0;
  var wrap: HTMLElement = canvas.parentElement ? canvas.parentElement : root;
  var CALC_W = 320, CALC_H = 200;
  var FIXED_DT = 16;
  var REDUCE_STEP_FRAMES = 40;
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var demo = !reduce;
  if (!demo) root.classList.remove('is-demo');
  function stopDemo(): void { demo = false; root.classList.remove('is-demo'); }
  var paused = false;
  var ownInput = false;
  var cw = 480, ch = 300, sc = 1.5, elapsed = 0, rafId = 0;
  var cleaners: Array<() => void> = [];

  function listen(target: EventTarget, type: string, fn: (e: Event) => void): void {
    target.addEventListener(type, fn);
    cleaners.push(function (): void { target.removeEventListener(type, fn); });
  }
  function clamp(v: number, lo: number, hi: number): number { return v < lo ? lo : (v > hi ? hi : v); }
  function setStatus(msg: string): void { statusEl.textContent = msg; }
  function hsl(h: number, s: number, l: number, a: number): string {
    return 'hsla(' + (h % 360) + ',' + s + '%,' + l + '%,' + a + ')';
  }
  function canvasPoint(e: PointerEvent): Pt {
    var r = canvas.getBoundingClientRect();
    return { x: (e.clientX - r.left) / r.width * CALC_W, y: (e.clientY - r.top) / r.height * CALC_H };
  }

  // 배경 — 어두운 잉크색 위에 방사형 빛무리를 (gx, gy) 에 깐다
  function beginDraw(inner: string, outer: string, gx: number, gy: number): void {
    ctx.setTransform(1, 0, 0, 1, 0, 0);
    ctx.fillStyle = '#1d1a2b';
    ctx.fillRect(0, 0, cw, ch);
    ctx.setTransform(sc, 0, 0, sc, 0, 0);
    var g = ctx.createRadialGradient(gx, gy, 8, gx, gy, 230);
    g.addColorStop(0, inner);
    g.addColorStop(1, outer);
    ctx.fillStyle = g;
    ctx.fillRect(0, 0, CALC_W, CALC_H);
  }
  function seg(x1: number, y1: number, x2: number, y2: number, w: number, col: string): void {
    ctx.beginPath();
    ctx.moveTo(x1, y1);
    ctx.lineTo(x2, y2);
    ctx.lineCap = 'round';
    ctx.lineWidth = w;
    ctx.strokeStyle = col;
    ctx.stroke();
  }
  function disc(x: number, y: number, r: number, col: string): void {
    ctx.beginPath();
    ctx.arc(x, y, r, 0, 6.2832);
    ctx.fillStyle = col;
    ctx.fill();
  }
  function glow(x: number, y: number, r: number, rgb: string, a: number): void {
    var g = ctx.createRadialGradient(x, y, 0, x, y, r);
    g.addColorStop(0, 'rgba(' + rgb + ',' + a + ')');
    g.addColorStop(1, 'rgba(' + rgb + ',0)');
    ctx.fillStyle = g;
    ctx.fillRect(x - r, y - r, r * 2, r * 2);
  }
  function drawTrail(arr: Pt[], rgb: string, w: number, alpha: number): void {
    ctx.lineCap = 'round';
    for (var i = 1; i < arr.length; i += 1) {
      var f = i / arr.length;
      ctx.beginPath();
      ctx.moveTo(arr[i - 1].x, arr[i - 1].y);
      ctx.lineTo(arr[i].x, arr[i].y);
      ctx.strokeStyle = 'rgba(' + rgb + ',' + (alpha * f * f) + ')';
      ctx.lineWidth = w * (0.3 + 0.7 * f);
      ctx.stroke();
    }
  }
  function pushTrail(arr: Pt[], x: number, y: number, max: number): void {
    arr.push({ x: x, y: y });
    if (arr.length > max) { arr.shift(); }
  }

  function defaultToggle(): void {
    if (reduce) {
      for (var i = 0; i < REDUCE_STEP_FRAMES; i += 1) { elapsed += FIXED_DT; stepFrame(); }
      draw();
      setStatus('한 장면씩 넘기는 중');
      return;
    }
    paused = !paused;
    btnEl.textContent = paused ? '재생' : '멈춤';
    setStatus(paused ? '일시정지됨' : '시연 중');
  }
  var onButton: () => void = defaultToggle;
  // 기법: 출발 각도를 OFFSET_STEP 에 번호를 곱한 식으로만 벌려 열여섯 진자를 한 식으로 적분하고, 번호를 색상에 그대로 대응시킨다
  var DT = 0.01;
  var SUBSTEPS = 3;
  var START_T1 = 2.4;
  var START_T2 = 2.2;
  var COUNT = 16;
  var OFFSET_STEP = 0.004;
  var HUE_SPAN = 300;
  var SIM_RESET_FRAMES = 340;
  var TRAIL_LEN = 26;
  var L1 = 1.0;
  var L2 = 1.0;
  var M1 = 1.0;
  var M2 = 1.0;
  var G = 9.81;
  var UNIT = 40, PIVOT_X = 160, PIVOT_Y = 74;
  var PREROLL_FRAMES = 40;
  // 라그랑주 운동방정식 — 각도는 아래 방향이 0, 시계 방향이 양수
  function accTheta1(t1: number, t2: number, w1: number, w2: number): number {
    var d = t1 - t2;
    var den = L1 * (2 * M1 + M2 - M2 * Math.cos(2 * d));
    return (-G * (2 * M1 + M2) * Math.sin(t1) - M2 * G * Math.sin(t1 - 2 * t2)
      - 2 * Math.sin(d) * M2 * (w2 * w2 * L2 + w1 * w1 * L1 * Math.cos(d))) / den;
  }
  function accTheta2(t1: number, t2: number, w1: number, w2: number): number {
    var d = t1 - t2;
    var den = L2 * (2 * M1 + M2 - M2 * Math.cos(2 * d));
    return (2 * Math.sin(d) * (w1 * w1 * L1 * (M1 + M2) + G * (M1 + M2) * Math.cos(t1)
      + w2 * w2 * L2 * M2 * Math.cos(d))) / den;
  }
  // 룽게-쿠타 4단계 — 한 걸음을 네 번 기울기로 평균 낸다 (s = [t1, t2, w1, w2])
  function rk4Step(s: number[], h: number): void {
    var t1 = s[0], t2 = s[1], w1 = s[2], w2 = s[3];
    var h2 = h * 0.5;
    var k1a = w1, k1b = w2, k1c = accTheta1(t1, t2, w1, w2), k1d = accTheta2(t1, t2, w1, w2);
    var u1 = t1 + h2 * k1a, u2 = t2 + h2 * k1b, u3 = w1 + h2 * k1c, u4 = w2 + h2 * k1d;
    var k2a = u3, k2b = u4, k2c = accTheta1(u1, u2, u3, u4), k2d = accTheta2(u1, u2, u3, u4);
    u1 = t1 + h2 * k2a; u2 = t2 + h2 * k2b; u3 = w1 + h2 * k2c; u4 = w2 + h2 * k2d;
    var k3a = u3, k3b = u4, k3c = accTheta1(u1, u2, u3, u4), k3d = accTheta2(u1, u2, u3, u4);
    u1 = t1 + h * k3a; u2 = t2 + h * k3b; u3 = w1 + h * k3c; u4 = w2 + h * k3d;
    var k4a = u3, k4b = u4, k4c = accTheta1(u1, u2, u3, u4), k4d = accTheta2(u1, u2, u3, u4);
    s[0] = t1 + h / 6 * (k1a + 2 * k2a + 2 * k3a + k4a);
    s[1] = t2 + h / 6 * (k1b + 2 * k2b + 2 * k3b + k4b);
    s[2] = w1 + h / 6 * (k1c + 2 * k2c + 2 * k3c + k4c);
    s[3] = w2 + h / 6 * (k1d + 2 * k2d + 2 * k3d + k4d);
  }
  function bobOne(s: number[], ox: number, oy: number): Pt {
    return { x: ox + UNIT * L1 * Math.sin(s[0]), y: oy + UNIT * L1 * Math.cos(s[0]) };
  }
  function bobTwo(s: number[], ox: number, oy: number): Pt {
    var a = bobOne(s, ox, oy);
    return { x: a.x + UNIT * L2 * Math.sin(s[1]), y: a.y + UNIT * L2 * Math.cos(s[1]) };
  }
  function drawArms(s: number[], ox: number, oy: number, c1: string, c2: string, w: number): void {
    var a = bobOne(s, ox, oy), b = bobTwo(s, ox, oy);
    seg(ox, oy, a.x, a.y, w, c1);
    seg(a.x, a.y, b.x, b.y, w, c2);
  }

  var fan: number[][] = [];
  var trails: Pt[][] = [];
  var frameCount = 0;

  function restart(): void {
    fan = [];
    trails = [];
    for (var i = 0; i < COUNT; i += 1) {
      fan.push([START_T1 + OFFSET_STEP * i, START_T2, 0, 0]);
      trails.push([]);
    }
    frameCount = 0;
  }
  restart();
  function stepFrame(): void {
    for (var i = 0; i < COUNT; i += 1) {
      for (var k = 0; k < SUBSTEPS; k += 1) { rk4Step(fan[i], DT); }
      var p = bobTwo(fan[i], PIVOT_X, PIVOT_Y);
      pushTrail(trails[i], p.x, p.y, TRAIL_LEN);
    }
    frameCount += 1;
    if (frameCount >= SIM_RESET_FRAMES) { restart(); }
  }
  function hueOf(i: number): number { return 330 + HUE_SPAN * i / (COUNT - 1); }

  function draw(): void {
    var lead = bobTwo(fan[COUNT >> 1], PIVOT_X, PIVOT_Y);
    beginDraw('#463e68', '#28223f', lead.x, lead.y);
    glow(lead.x, lead.y, 100, '255,238,252', 0.22);
    for (var i = 0; i < COUNT; i += 1) {
      var col = hsl(hueOf(i), 85, 80, 1);
      var p = bobTwo(fan[i], PIVOT_X, PIVOT_Y);
      drawTrail(trails[i], '255,255,255', 2.2, 0.25);
      ctx.lineCap = 'round';
      for (var j = 1; j < trails[i].length; j += 1) {
        var f = j / trails[i].length;
        ctx.beginPath();
        ctx.moveTo(trails[i][j - 1].x, trails[i][j - 1].y);
        ctx.lineTo(trails[i][j].x, trails[i][j].y);
        ctx.strokeStyle = hsl(hueOf(i), 85, 80, 0.6 * f);
        ctx.lineWidth = 1 + 1.6 * f;
        ctx.stroke();
      }
      drawArms(fan[i], PIVOT_X, PIVOT_Y, hsl(hueOf(i), 80, 82, 0.5), hsl(hueOf(i), 80, 82, 0.7), 1.4);
      glow(p.x, p.y, 10, '255,255,255', 0.35);
      disc(p.x, p.y, 3.2, col);
    }
    disc(PIVOT_X, PIVOT_Y, 4.5, '#fff1c9');
  }

  function fit(): void {
    var r = wrap.getBoundingClientRect();
    cw = Math.max(1, Math.round(r.width));
    ch = Math.max(1, Math.round(r.height));
    canvas.width = cw;
    canvas.height = ch;
    sc = cw / CALC_W;
    draw();
  }
  var lastTs: number | null = null;
  var accMs = 0;
  function tick(ts: number): void {
    if (lastTs === null) { lastTs = ts; }
    var frameDt = Math.min(ts - lastTs, 48);
    lastTs = ts;
    if (!paused) {
      accMs += frameDt;
      while (accMs >= FIXED_DT) { elapsed += FIXED_DT; stepFrame(); accMs -= FIXED_DT; }
    }
    draw();
    rafId = requestAnimationFrame(tick);
  }
  for (var w0 = 0; w0 < PREROLL_FRAMES; w0 += 1) { elapsed += FIXED_DT; stepFrame(); }
  fit();
  listen(window, 'resize', fit);
  listen(btnEl, 'click', function (): void { onButton(); });
  if (!ownInput) {
    listen(canvas, 'pointerdown', function (): void { onButton(); });
    listen(canvas, 'keydown', function (e: Event): void {
      var k = (e as KeyboardEvent).key;
      if (k === 'Enter' || k === ' ') { e.preventDefault(); onButton(); }
    });
  }
  if (reduce) {
    if (!ownInput) { btnEl.textContent = '다음 장면'; setStatus('한 장면씩 넘기는 중'); }
  } else {
    rafId = requestAnimationFrame(tick);
  }

  function destroy(): void {
    cancelAnimationFrame(rafId);
    for (var i = 0; i < cleaners.length; i += 1) { cleaners[i](); }
  }
  return destroy;
}


export default function DpSixteenFanEnsembleHueSpread() {
  const rootRef = useRef<HTMLDivElement | null>(null);
  const canvasRef = useRef<HTMLCanvasElement | null>(null);
  const statusRef = useRef<HTMLParagraphElement | null>(null);
  const btnRef = useRef<HTMLButtonElement | null>(null);

  useEffect(() => {
    const root = rootRef.current;
    const canvas = canvasRef.current;
    const statusEl = statusRef.current;
    const btnEl = btnRef.current;
    if (!root || !canvas || !statusEl || !btnEl) return;
    return main(root, canvas, statusEl, btnEl);
  }, []);

  return (
    <main className={styles.stage}>
      <div className={`${styles.bp} is-demo`} ref={rootRef}>
        <canvas className={styles.bp__canvas} ref={canvasRef} width={480} height={300} tabIndex={0} aria-label="출발 각도를 번호에 비례해 조금씩 벌린 열여섯 진자를 색상 순서대로 겹쳐 그려, 한 점에서 출발한 무지개가 어느 순간 흩어지며 엉키는 장면을 보인다." />
        <p className={styles.bp__status} ref={statusRef} aria-live="polite">시연 중</p>
        <button className={styles.bp__btn} ref={btnRef} type="button">멈춤</button>
        <p className={styles.bp__caption}>출발 각도를 번호에 비례해 조금씩 벌린 열여섯 진자를 색상 순서대로 겹쳐 그려, 한 점에서 출발한 무지개가 어느 순간 흩어지며 엉키는 장면을 보인다.</p>
      </div>
    </main>
  );
}