09文字の帯が正弦波の曲線の上を横へ流れ、文字ごとに曲線の傾きだけ回り、速さが増すと波が高くなる文字のリボン

<main class="stage">
<div class="hs is-demo" id="hs">
  <canvas class="hs__canvas" data-role="canvas" width="480" height="300" tabindex="0" aria-label="波の曲線に沿って流れる文字が曲線の傾きの分だけ回り、速くなると波が大きくなるリボン"></canvas>
  <p class="hs__status" data-role="status" aria-live="off">流れています</p>
  <div class="hs__tools">
    <button class="hs__btn" data-role="btn" type="button" aria-pressed="false">停止</button>
  </div>
</div>
</main>

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

.hs {
  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: $subject-ink;
}

.hs__canvas {
  display: block;
  width: 100%;
  height: 100%;
  cursor: grab;
}

.hs__canvas:active {
  cursor: grabbing;
}

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

.hs__status {
  position: absolute;
  left: $sp-3;
  bottom: $sp-3;
  max-width: 46%;
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-control;
  background: rgba(255, 255, 255, .85);
  color: $subject-ink;
  font-weight: 500;
  font-size: 11px;
  line-height: 1.4;
  pointer-events: none;
}

.hs__tools {
  position: absolute;
  right: $sp-3;
  bottom: $sp-3;
  display: flex;
  gap: $sp-2;
}

.hs__btn {
  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;
  transition: background-color $dur-quick ease-out;
}

.hs__btn:hover {
  background: $subject-cream;
}

.hs__btn[aria-pressed="true"] {
  background: $subject-mint;
}

.hs__btn:focus-visible {
  outline: 2px solid rgba(255, 255, 255, .95);
  outline-offset: 2px;
}

// 손가락 가로 끌기는 이 캔버스가 받고, 세로 쓸기는 브라우저에 남겨 페이지 스크롤이 막히지 않게 한다
.hs__canvas { touch-action: pan-y; }

@media (max-width: 340px) {
  .hs__btn { font-size: 10px; padding: $sp-1 $sp-2; }
  .hs__status { font-size: 10px; padding: $sp-1 $sp-2; }
}

@media (prefers-reduced-motion: reduce) {
  .hs__btn { transition: none; }
}

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);
}

.hs {
  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;
}

.hs__canvas {
  display: block;
  width: 100%;
  height: 100%;
  cursor: grab;
}

.hs__canvas:active {
  cursor: grabbing;
}

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

.hs__status {
  position: absolute;
  left: 12px;
  bottom: 12px;
  max-width: 46%;
  margin: 0;
  padding: 4px 12px;
  border-radius: 12px;
  background: rgba(255, 255, 255, 0.85);
  color: #17141a;
  font-weight: 500;
  font-size: 11px;
  line-height: 1.4;
  pointer-events: none;
}

.hs__tools {
  position: absolute;
  right: 12px;
  bottom: 12px;
  display: flex;
  gap: 8px;
}

.hs__btn {
  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;
  transition: background-color 220ms ease-out;
}

.hs__btn:hover {
  background: #fff7e6;
}

.hs__btn[aria-pressed=true] {
  background: #4cd4a6;
}

.hs__btn:focus-visible {
  outline: 2px solid rgba(255, 255, 255, 0.95);
  outline-offset: 2px;
}

.hs__canvas {
  touch-action: pan-y;
}

@media (max-width: 340px) {
  .hs__btn {
    font-size: 10px;
    padding: 4px 8px;
  }
  .hs__status {
    font-size: 10px;
    padding: 4px 8px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .hs__btn {
    transition: none;
  }
}

(function () {
    const root = document.getElementById("hs");
    if (!root) return;
    const W = 480;
    const H = 300;
    const FIXED_DT = 16;
    // 파스텔 팔레트 — 어두운 무대 위에 밝은 카드를 얹어 명도 차로 읽힌다
    const BG = [29, 26, 44];
    const PAPER = [255, 248, 234];
    const INK = [58, 48, 76];
    const MINT = [126, 226, 192];
    const SKY = [124, 196, 255];
    const LILAC = [190, 164, 255];
    const PINK = [255, 160, 190];
    const PEACH = [255, 208, 168];
    const TINTS = [SKY, PINK, MINT, LILAC, PEACH];
    function clamp(v, lo, hi) { return v < lo ? lo : (v > hi ? hi : v); }
    function lerp(a, b, k) { return a + (b - a) * k; }
    function smooth(x) { const c = clamp(x, 0, 1); return c * c * (3 - 2 * c); }
    function rgba(c, a) {
        return 'rgba(' + Math.round(c[0]) + ',' + Math.round(c[1]) + ',' + Math.round(c[2]) + ',' + clamp(a, 0, 1).toFixed(3) + ')';
    }
    function mix(a, b, k) { return [lerp(a[0], b[0], k), lerp(a[1], b[1], k), lerp(a[2], b[2], k)]; }
    const canvasEl = root.querySelector('[data-role="canvas"]');
    const statusEl = root.querySelector('[data-role="status"]');
    const ctxRaw = canvasEl ? canvasEl.getContext('2d') : null;
    if (!canvasEl || !ctxRaw || !statusEl) {
        return;
    }
    const cv = canvasEl;
    const ctx = ctxRaw;
    const status = statusEl;
    const reduceQuery = window.matchMedia('(prefers-reduced-motion: reduce)');
    const still = reduceQuery.matches;
    // 자동 시연 중인가 — 사람이 처음 만지는 순간 시연을 멈추고 상태 줄을 읽어 주기 시작한다
    let demo = root.classList.contains('is-demo');
    function wake() {
        if (!demo) {
            return;
        }
        demo = false;
        root.classList.remove('is-demo');
        status.setAttribute('aria-live', 'polite');
    }
    function say(text) {
        if (status.textContent !== text) {
            status.textContent = text;
        }
    }
    // 휠 한 번의 이동량을 px 로 — 줄 단위(deltaMode 1)·쪽 단위(deltaMode 2) 장치도 같은 눈금으로 맞춘다.
    // 가로·세로 중 큰 쪽을 쓴다: 트랙패드의 가로 쓸기와 마우스 휠의 세로 굴림이 같은 방향으로 들어온다
    function wheelPx(ev) {
        const unit = ev.deltaMode === 1 ? 16 : (ev.deltaMode === 2 ? W : 1);
        const d = Math.abs(ev.deltaX) > Math.abs(ev.deltaY) ? ev.deltaX : ev.deltaY;
        return d * unit;
    }
    // 시연 시계가 loop 주기 안의 at 시각을 이번 스텝에 막 지났는가
    function crossed(t, at, loop) {
        const p = t % loop;
        return p >= at && p - FIXED_DT < at;
    }
    function fitCanvas() {
        const dpr = window.devicePixelRatio || 1;
        cv.width = Math.round(W * dpr);
        cv.height = Math.round(H * dpr);
        ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
    }
    function onResize() {
        fitCanvas();
        draw();
    }
    fitCanvas();
    window.addEventListener('resize', onResize);
    // 화면 좌표(CSS px) → 장면 좌표(480x300). 리사이즈 뒤에도 늘 현재 크기로 다시 잰다
    function toScene(ev) {
        const r = cv.getBoundingClientRect();
        return [((ev.clientX - r.left) / r.width) * W, ((ev.clientY - r.top) / r.height) * H];
    }
    function roundRectPath(c, x, y, w, h, r) {
        const rr = Math.min(r, w / 2, h / 2);
        c.beginPath();
        c.moveTo(x + rr, y);
        c.lineTo(x + w - rr, y);
        c.quadraticCurveTo(x + w, y, x + w, y + rr);
        c.lineTo(x + w, y + h - rr);
        c.quadraticCurveTo(x + w, y + h, x + w - rr, y + h);
        c.lineTo(x + rr, y + h);
        c.quadraticCurveTo(x, y + h, x, y + h - rr);
        c.lineTo(x, y + rr);
        c.quadraticCurveTo(x, y, x + rr, y);
        c.closePath();
    }
    // 카드 한 장 — 사진 대신 계산한 그림 칸(그라디언트 하늘·해·언덕) + 글줄 막대 두 개 + 번호
    function drawCard(c, x, y, w, h, i, light) {
        const t1 = TINTS[i % TINTS.length];
        const t2 = TINTS[(i + 2) % TINTS.length];
        const k = clamp(light, 0, 1);
        roundRectPath(c, x, y, w, h, 10);
        c.fillStyle = rgba(mix(BG, PAPER, k), 1);
        c.fill();
        const ih = h * 0.58;
        const g = c.createLinearGradient(x, y, x + w, y + ih);
        g.addColorStop(0, rgba(mix(BG, t1, k), 1));
        g.addColorStop(1, rgba(mix(BG, t2, k * 0.92), 1));
        c.save();
        roundRectPath(c, x + 6, y + 6, w - 12, ih - 6, 7);
        c.fillStyle = g;
        c.fill();
        c.clip();
        c.fillStyle = rgba(mix(BG, PAPER, k * 0.9), 0.9);
        c.beginPath();
        c.arc(x + w * 0.7, y + ih * 0.36, Math.min(w, ih) * 0.13, 0, Math.PI * 2);
        c.fill();
        c.fillStyle = rgba(mix(BG, INK, k), 0.55);
        c.beginPath();
        c.moveTo(x, y + ih);
        c.lineTo(x + w * 0.32, y + ih * 0.55);
        c.lineTo(x + w * 0.55, y + ih * 0.8);
        c.lineTo(x + w * 0.78, y + ih * 0.62);
        c.lineTo(x + w, y + ih);
        c.closePath();
        c.fill();
        c.restore();
        c.fillStyle = rgba(mix(BG, INK, k), 0.75);
        c.fillRect(x + 10, y + ih + 12, w * 0.62, 6);
        c.fillStyle = rgba(mix(BG, INK, k), 0.4);
        c.fillRect(x + 10, y + ih + 24, w * 0.44, 5);
        c.fillStyle = rgba(mix(BG, INK, k), 0.9);
        c.font = '700 13px sans-serif';
        c.textAlign = 'right';
        c.textBaseline = 'alphabetic';
        c.fillText(String(i + 1).padStart(2, '0'), x + w - 9, y + h - 10);
    }
    const RIBBON_TEXT = '横へ流れる文字のリボン · 横スクロール ·';
    const FONT_PX = 30;
    const BASE_SPEED = 60;
    const MAX_SPEED = 720;
    const SPEED_GAIN = 3;
    const SPEED_FRICTION = 0.965;
    const WAVE_K = (Math.PI * 2) / 260;
    const WAVE_DRIFT = 1.6;
    const AMP_MIN = 10;
    const AMP_GAIN = 0.09;
    const AMP_MAX = 58;
    const AMP_LERP = 0.05;
    const CY = 136;
    const X0 = -80;
    const DEMO_LOOP = 4000;
    const TXT_FLOW = '流れています';
    const TXT_FAST = '速く流れる — 波が大きくなる';
    const TXT_PAUSE = '停止';
    const pauseBtn = root.querySelector('[data-role="btn"]');
    let extra = 0;
    let flow = 0;
    let amp = AMP_MIN;
    let phase = 0;
    let paused = false;
    let fastSaid = false;
    ctx.font = '800 ' + FONT_PX + 'px sans-serif';
    // 끝에 빈칸 하나를 붙여 되풀이 이음매에 간격을 둔다
    const glyphs = Array.from(RIBBON_TEXT + ' ');
    const widths = glyphs.map(function (g) { return ctx.measureText(g).width; });
    const offsets = [];
    let textLen = 0;
    for (let i = 0; i < widths.length; i += 1) {
        offsets.push(textLen);
        textLen += widths[i];
    }
    function speedNow() { return paused ? 0 : clamp(BASE_SPEED + extra, -MAX_SPEED, MAX_SPEED); }
    // 물결 곡선과 그 도함수(기울기) — 글자 회전각은 atan(기울기)
    function waveY(x) { return CY + amp * Math.sin(WAVE_K * x + phase); }
    function waveSlope(x) { return amp * WAVE_K * Math.cos(WAVE_K * x + phase); }
    // 흐름 속도 → 물결 높이 목표. 실제 높이는 이 값을 저역 통과(AMP_LERP)로 천천히 따라간다
    function ampTarget(speed) { return clamp(AMP_MIN + AMP_GAIN * Math.abs(speed), AMP_MIN, AMP_MAX); }
    function canMove(d) {
        const s = speedNow();
        return d > 0 ? s < MAX_SPEED : s > -MAX_SPEED;
    }
    function step() {
        const dt = FIXED_DT / 1000;
        extra *= SPEED_FRICTION;
        const s = speedNow();
        flow += s * dt;
        phase += WAVE_DRIFT * dt * (paused ? 0 : 1);
        amp += (ampTarget(s) - amp) * AMP_LERP;
        if (amp > 34 && !fastSaid) {
            fastSaid = true;
            say(TXT_FAST);
        }
        if (amp < 20 && fastSaid) {
            fastSaid = false;
            say(paused ? TXT_PAUSE : TXT_FLOW);
        }
    }
    function settle() {
        amp = AMP_MIN;
        say(TXT_FLOW);
    }
    function demoTick(t) {
        for (let k = 0; k < 4; k += 1) {
            if (crossed(t, 200 + k * 40, DEMO_LOOP)) {
                extra += 100 * SPEED_GAIN;
            }
        }
    }
    function draw() {
        ctx.fillStyle = rgba(BG, 1);
        ctx.fillRect(0, 0, W, H);
        // 리본 띠 — 곡선을 굵은 선으로 깔아 글자 아래 바탕이 된다
        ctx.strokeStyle = rgba(mix(BG, LILAC, 0.42), 1);
        ctx.lineWidth = 50;
        ctx.lineCap = 'round';
        ctx.beginPath();
        for (let x = -20; x <= W + 20; x += 6) {
            if (x === -20) {
                ctx.moveTo(x, waveY(x));
            }
            else {
                ctx.lineTo(x, waveY(x));
            }
        }
        ctx.stroke();
        ctx.strokeStyle = rgba(mix(BG, PAPER, 0.25), 0.6);
        ctx.lineWidth = 1;
        ctx.setLineDash([3, 7]);
        ctx.beginPath();
        for (let x = -20; x <= W + 20; x += 6) {
            if (x === -20) {
                ctx.moveTo(x, waveY(x) + 31);
            }
            else {
                ctx.lineTo(x, waveY(x) + 31);
            }
        }
        ctx.stroke();
        ctx.setLineDash([]);
        // 글자 — 곡선을 따라 호의 길이만큼 걸어가며 놓는다(dx = 걸음 / √(1 + 기울기²))
        ctx.font = '800 ' + FONT_PX + 'px sans-serif';
        ctx.textAlign = 'center';
        ctx.textBaseline = 'middle';
        const shift = ((flow % textLen) + textLen) % textLen;
        let x = X0;
        let arc = 0;
        let done = false;
        for (let r = 0; r < 8 && !done; r += 1) {
            for (let g = 0; g < glyphs.length; g += 1) {
                const want = offsets[g] + widths[g] / 2 + r * textLen - shift;
                if (want < 0) {
                    continue;
                }
                while (arc < want) {
                    const sl = waveSlope(x);
                    const ds = Math.min(4, want - arc);
                    x += ds / Math.sqrt(1 + sl * sl);
                    arc += ds;
                }
                if (x > W + 40) {
                    done = true;
                    break;
                }
                ctx.save();
                ctx.translate(x, waveY(x));
                ctx.rotate(Math.atan(waveSlope(x)));
                ctx.fillStyle = rgba(TINTS[(g + r) % TINTS.length], 1);
                ctx.fillText(glyphs[g], 0, 0);
                ctx.restore();
            }
        }
        // 속도 눈금
        const s = speedNow();
        ctx.fillStyle = rgba(mix(BG, PAPER, 0.14), 1);
        ctx.fillRect(24, 24, W - 48, 4);
        ctx.fillStyle = rgba(PEACH, 1);
        const sw = ((W - 48) / 2) * (s / MAX_SPEED);
        ctx.fillRect(W / 2 + Math.min(0, sw), 24, Math.abs(sw), 4);
    }
    function onWheel(ev) {
        const d = wheelPx(ev);
        // 속도가 이미 끝까지 올랐으면 가로채지 않는다
        if (d === 0 || !canMove(d)) {
            return;
        }
        ev.preventDefault();
        wake();
        if (still) {
            flow += d;
            draw();
            return;
        }
        extra = clamp(extra + d * SPEED_GAIN, -MAX_SPEED * 2, MAX_SPEED * 2);
    }
    cv.addEventListener('wheel', onWheel, { passive: false });
    let dragId = -1;
    let dragX = 0;
    let dragT = 0;
    let dragSpeed = 0;
    cv.addEventListener('pointerdown', function (ev) {
        wake();
        dragId = ev.pointerId;
        cv.setPointerCapture(ev.pointerId);
        dragX = toScene(ev)[0];
        dragT = ev.timeStamp;
        dragSpeed = 0;
    });
    cv.addEventListener('pointermove', function (ev) {
        if (ev.pointerId !== dragId) {
            return;
        }
        const sx = toScene(ev)[0];
        const dt = Math.max(1, ev.timeStamp - dragT) / 1000;
        // 왼쪽으로 끌면 글자가 왼쪽으로 — 흐름 값을 늘린다
        flow -= sx - dragX;
        dragSpeed = lerp(dragSpeed, -(sx - dragX) / dt, 0.4);
        dragX = sx;
        dragT = ev.timeStamp;
        if (still) {
            draw();
        }
    });
    function endDrag(ev) {
        if (ev.pointerId !== dragId) {
            return;
        }
        dragId = -1;
        if (!still) {
            extra = clamp(dragSpeed - BASE_SPEED, -MAX_SPEED * 2, MAX_SPEED * 2);
        }
    }
    cv.addEventListener('pointerup', endDrag);
    cv.addEventListener('pointercancel', endDrag);
    cv.addEventListener('keydown', function (ev) {
        let d = 0;
        if (ev.key === 'ArrowRight') {
            d = 1;
        }
        else if (ev.key === 'ArrowLeft') {
            d = -1;
        }
        if (d === 0 || !canMove(d)) {
            return;
        }
        ev.preventDefault();
        wake();
        if (still) {
            flow += d * 60;
            draw();
            return;
        }
        extra += d * 240;
    });
    if (pauseBtn) {
        pauseBtn.addEventListener('click', function () {
            wake();
            paused = !paused;
            if (paused) {
                extra = 0;
            }
            pauseBtn.setAttribute('aria-pressed', paused ? 'true' : 'false');
            say(paused ? TXT_PAUSE : TXT_FLOW);
        });
    }
    say(TXT_FLOW);
    let rafId = 0;
    let lastTs = -1;
    let acc = 0;
    let clock = 0;
    function frame(ts) {
        if (lastTs < 0) {
            lastTs = ts;
        }
        // 탭이 숨었다 돌아와도 한 번에 100ms 까지만 따라잡는다 — 순간이동 대신 이어서 움직인다
        acc += Math.min(ts - lastTs, 100);
        lastTs = ts;
        let n = 0;
        while (acc >= FIXED_DT && n < 6) {
            clock += FIXED_DT;
            if (demo) {
                demoTick(clock);
            }
            step();
            acc -= FIXED_DT;
            n += 1;
        }
        draw();
        rafId = window.requestAnimationFrame(frame);
    }
    if (still) {
        settle();
        draw();
    }
    else {
        rafId = window.requestAnimationFrame(frame);
    }
    return function () {
        window.cancelAnimationFrame(rafId);
        window.removeEventListener('resize', onResize);
    };
})();

// HscWavePathTextRibbonTangent - vanilla 판(09-hsc-wave-path-text-ribbon-tangent) 의 React 포트. 같은 계산을 useEffect 안에서 돌린다.
import { useEffect, useRef } from "react";
import styles from "./HscWavePathTextRibbonTangent.module.scss";

const cx = (s: string): string => s.split(" ").map((n) => styles[n] ?? n).join(" ");

export default function HscWavePathTextRibbonTangent() {
  const rootRef = useRef<HTMLDivElement | null>(null);

  useEffect(() => {
    const rootEl = rootRef.current;
    if (!rootEl) return;
    const root: HTMLElement = rootEl;
    type RGB = [number, number, number];
    const W = 480;
    const H = 300;
    const FIXED_DT = 16;
    // 파스텔 팔레트 — 어두운 무대 위에 밝은 카드를 얹어 명도 차로 읽힌다
    const BG: RGB = [29, 26, 44];
    const PAPER: RGB = [255, 248, 234];
    const INK: RGB = [58, 48, 76];
    const MINT: RGB = [126, 226, 192];
    const SKY: RGB = [124, 196, 255];
    const LILAC: RGB = [190, 164, 255];
    const PINK: RGB = [255, 160, 190];
    const PEACH: RGB = [255, 208, 168];
    const TINTS: RGB[] = [SKY, PINK, MINT, LILAC, PEACH];
    function clamp(v: number, lo: number, hi: number): number { return v < lo ? lo : (v > hi ? hi : v); }
    function lerp(a: number, b: number, k: number): number { return a + (b - a) * k; }
    function smooth(x: number): number { const c = clamp(x, 0, 1); return c * c * (3 - 2 * c); }
    function rgba(c: RGB, a: number): string {
        return 'rgba(' + Math.round(c[0]) + ',' + Math.round(c[1]) + ',' + Math.round(c[2]) + ',' + clamp(a, 0, 1).toFixed(3) + ')';
    }
    function mix(a: RGB, b: RGB, k: number): RGB { return [lerp(a[0], b[0], k), lerp(a[1], b[1], k), lerp(a[2], b[2], k)]; }
    const canvasEl = root.querySelector('[data-role="canvas"]') as HTMLCanvasElement | null;
    const statusEl = root.querySelector('[data-role="status"]') as HTMLElement | null;
    const ctxRaw = canvasEl ? canvasEl.getContext('2d') : null;
    if (!canvasEl || !ctxRaw || !statusEl) { return; }
    const cv: HTMLCanvasElement = canvasEl;
    const ctx: CanvasRenderingContext2D = ctxRaw;
    const status: HTMLElement = statusEl;
    const reduceQuery = window.matchMedia('(prefers-reduced-motion: reduce)');
    const still = reduceQuery.matches;
    // 자동 시연 중인가 — 사람이 처음 만지는 순간 시연을 멈추고 상태 줄을 읽어 주기 시작한다
    let demo = root.classList.contains('is-demo');
    function wake(): void {
        if (!demo) { return; }
        demo = false;
        root.classList.remove('is-demo');
        status.setAttribute('aria-live', 'polite');
    }
    function say(text: string): void {
        if (status.textContent !== text) { status.textContent = text; }
    }
    // 휠 한 번의 이동량을 px 로 — 줄 단위(deltaMode 1)·쪽 단위(deltaMode 2) 장치도 같은 눈금으로 맞춘다.
    // 가로·세로 중 큰 쪽을 쓴다: 트랙패드의 가로 쓸기와 마우스 휠의 세로 굴림이 같은 방향으로 들어온다
    function wheelPx(ev: WheelEvent): number {
        const unit = ev.deltaMode === 1 ? 16 : (ev.deltaMode === 2 ? W : 1);
        const d = Math.abs(ev.deltaX) > Math.abs(ev.deltaY) ? ev.deltaX : ev.deltaY;
        return d * unit;
    }
    // 시연 시계가 loop 주기 안의 at 시각을 이번 스텝에 막 지났는가
    function crossed(t: number, at: number, loop: number): boolean {
        const p = t % loop;
        return p >= at && p - FIXED_DT < at;
    }
    function fitCanvas(): void {
        const dpr = window.devicePixelRatio || 1;
        cv.width = Math.round(W * dpr);
        cv.height = Math.round(H * dpr);
        ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
    }
    function onResize(): void {
        fitCanvas();
        draw();
    }
    fitCanvas();
    window.addEventListener('resize', onResize);
    // 화면 좌표(CSS px) → 장면 좌표(480x300). 리사이즈 뒤에도 늘 현재 크기로 다시 잰다
    function toScene(ev: PointerEvent): [number, number] {
        const r = cv.getBoundingClientRect();
        return [((ev.clientX - r.left) / r.width) * W, ((ev.clientY - r.top) / r.height) * H];
    }
    function roundRectPath(c: CanvasRenderingContext2D, x: number, y: number, w: number, h: number, r: number): void {
        const rr = Math.min(r, w / 2, h / 2);
        c.beginPath();
        c.moveTo(x + rr, y);
        c.lineTo(x + w - rr, y);
        c.quadraticCurveTo(x + w, y, x + w, y + rr);
        c.lineTo(x + w, y + h - rr);
        c.quadraticCurveTo(x + w, y + h, x + w - rr, y + h);
        c.lineTo(x + rr, y + h);
        c.quadraticCurveTo(x, y + h, x, y + h - rr);
        c.lineTo(x, y + rr);
        c.quadraticCurveTo(x, y, x + rr, y);
        c.closePath();
    }
    // 카드 한 장 — 사진 대신 계산한 그림 칸(그라디언트 하늘·해·언덕) + 글줄 막대 두 개 + 번호
    function drawCard(c: CanvasRenderingContext2D, x: number, y: number, w: number, h: number, i: number, light: number): void {
        const t1 = TINTS[i % TINTS.length];
        const t2 = TINTS[(i + 2) % TINTS.length];
        const k = clamp(light, 0, 1);
        roundRectPath(c, x, y, w, h, 10);
        c.fillStyle = rgba(mix(BG, PAPER, k), 1);
        c.fill();
        const ih = h * 0.58;
        const g = c.createLinearGradient(x, y, x + w, y + ih);
        g.addColorStop(0, rgba(mix(BG, t1, k), 1));
        g.addColorStop(1, rgba(mix(BG, t2, k * 0.92), 1));
        c.save();
        roundRectPath(c, x + 6, y + 6, w - 12, ih - 6, 7);
        c.fillStyle = g;
        c.fill();
        c.clip();
        c.fillStyle = rgba(mix(BG, PAPER, k * 0.9), 0.9);
        c.beginPath();
        c.arc(x + w * 0.7, y + ih * 0.36, Math.min(w, ih) * 0.13, 0, Math.PI * 2);
        c.fill();
        c.fillStyle = rgba(mix(BG, INK, k), 0.55);
        c.beginPath();
        c.moveTo(x, y + ih);
        c.lineTo(x + w * 0.32, y + ih * 0.55);
        c.lineTo(x + w * 0.55, y + ih * 0.8);
        c.lineTo(x + w * 0.78, y + ih * 0.62);
        c.lineTo(x + w, y + ih);
        c.closePath();
        c.fill();
        c.restore();
        c.fillStyle = rgba(mix(BG, INK, k), 0.75);
        c.fillRect(x + 10, y + ih + 12, w * 0.62, 6);
        c.fillStyle = rgba(mix(BG, INK, k), 0.4);
        c.fillRect(x + 10, y + ih + 24, w * 0.44, 5);
        c.fillStyle = rgba(mix(BG, INK, k), 0.9);
        c.font = '700 13px sans-serif';
        c.textAlign = 'right';
        c.textBaseline = 'alphabetic';
        c.fillText(String(i + 1).padStart(2, '0'), x + w - 9, y + h - 10);
    }
    const RIBBON_TEXT = '옆으로 흐르는 글자 리본 · 가로 스크롤 ·';
    const FONT_PX = 30;
    const BASE_SPEED = 60;
    const MAX_SPEED = 720;
    const SPEED_GAIN = 3;
    const SPEED_FRICTION = 0.965;
    const WAVE_K = (Math.PI * 2) / 260;
    const WAVE_DRIFT = 1.6;
    const AMP_MIN = 10;
    const AMP_GAIN = 0.09;
    const AMP_MAX = 58;
    const AMP_LERP = 0.05;
    const CY = 136;
    const X0 = -80;
    const DEMO_LOOP = 4000;
    const TXT_FLOW = '흐르는 중';
    const TXT_FAST = '빨리 흐름 — 물결이 커짐';
    const TXT_PAUSE = '멈춤';
    const pauseBtn = root.querySelector('[data-role="btn"]') as HTMLButtonElement | null;
    let extra = 0;
    let flow = 0;
    let amp = AMP_MIN;
    let phase = 0;
    let paused = false;
    let fastSaid = false;
    ctx.font = '800 ' + FONT_PX + 'px sans-serif';
    // 끝에 빈칸 하나를 붙여 되풀이 이음매에 간격을 둔다
    const glyphs: string[] = Array.from(RIBBON_TEXT + ' ');
    const widths: number[] = glyphs.map(function (g: string): number { return ctx.measureText(g).width; });
    const offsets: number[] = [];
    let textLen = 0;
    for (let i = 0; i < widths.length; i += 1) { offsets.push(textLen); textLen += widths[i]; }
    function speedNow(): number { return paused ? 0 : clamp(BASE_SPEED + extra, -MAX_SPEED, MAX_SPEED); }
    // 물결 곡선과 그 도함수(기울기) — 글자 회전각은 atan(기울기)
    function waveY(x: number): number { return CY + amp * Math.sin(WAVE_K * x + phase); }
    function waveSlope(x: number): number { return amp * WAVE_K * Math.cos(WAVE_K * x + phase); }
    // 흐름 속도 → 물결 높이 목표. 실제 높이는 이 값을 저역 통과(AMP_LERP)로 천천히 따라간다
    function ampTarget(speed: number): number { return clamp(AMP_MIN + AMP_GAIN * Math.abs(speed), AMP_MIN, AMP_MAX); }
    function canMove(d: number): boolean {
        const s = speedNow();
        return d > 0 ? s < MAX_SPEED : s > -MAX_SPEED;
    }
    function step(): void {
        const dt = FIXED_DT / 1000;
        extra *= SPEED_FRICTION;
        const s = speedNow();
        flow += s * dt;
        phase += WAVE_DRIFT * dt * (paused ? 0 : 1);
        amp += (ampTarget(s) - amp) * AMP_LERP;
        if (amp > 34 && !fastSaid) { fastSaid = true; say(TXT_FAST); }
        if (amp < 20 && fastSaid) { fastSaid = false; say(paused ? TXT_PAUSE : TXT_FLOW); }
    }
    function settle(): void {
        amp = AMP_MIN;
        say(TXT_FLOW);
    }
    function demoTick(t: number): void {
        for (let k = 0; k < 4; k += 1) { if (crossed(t, 200 + k * 40, DEMO_LOOP)) { extra += 100 * SPEED_GAIN; } }
    }
    function draw(): void {
        ctx.fillStyle = rgba(BG, 1);
        ctx.fillRect(0, 0, W, H);
        // 리본 띠 — 곡선을 굵은 선으로 깔아 글자 아래 바탕이 된다
        ctx.strokeStyle = rgba(mix(BG, LILAC, 0.42), 1);
        ctx.lineWidth = 50;
        ctx.lineCap = 'round';
        ctx.beginPath();
        for (let x = -20; x <= W + 20; x += 6) {
            if (x === -20) { ctx.moveTo(x, waveY(x)); } else { ctx.lineTo(x, waveY(x)); }
        }
        ctx.stroke();
        ctx.strokeStyle = rgba(mix(BG, PAPER, 0.25), 0.6);
        ctx.lineWidth = 1;
        ctx.setLineDash([3, 7]);
        ctx.beginPath();
        for (let x = -20; x <= W + 20; x += 6) {
            if (x === -20) { ctx.moveTo(x, waveY(x) + 31); } else { ctx.lineTo(x, waveY(x) + 31); }
        }
        ctx.stroke();
        ctx.setLineDash([]);
        // 글자 — 곡선을 따라 호의 길이만큼 걸어가며 놓는다(dx = 걸음 / √(1 + 기울기²))
        ctx.font = '800 ' + FONT_PX + 'px sans-serif';
        ctx.textAlign = 'center';
        ctx.textBaseline = 'middle';
        const shift = ((flow % textLen) + textLen) % textLen;
        let x = X0;
        let arc = 0;
        let done = false;
        for (let r = 0; r < 8 && !done; r += 1) {
            for (let g = 0; g < glyphs.length; g += 1) {
                const want = offsets[g] + widths[g] / 2 + r * textLen - shift;
                if (want < 0) { continue; }
                while (arc < want) {
                    const sl = waveSlope(x);
                    const ds = Math.min(4, want - arc);
                    x += ds / Math.sqrt(1 + sl * sl);
                    arc += ds;
                }
                if (x > W + 40) { done = true; break; }
                ctx.save();
                ctx.translate(x, waveY(x));
                ctx.rotate(Math.atan(waveSlope(x)));
                ctx.fillStyle = rgba(TINTS[(g + r) % TINTS.length], 1);
                ctx.fillText(glyphs[g], 0, 0);
                ctx.restore();
            }
        }
        // 속도 눈금
        const s = speedNow();
        ctx.fillStyle = rgba(mix(BG, PAPER, 0.14), 1);
        ctx.fillRect(24, 24, W - 48, 4);
        ctx.fillStyle = rgba(PEACH, 1);
        const sw = ((W - 48) / 2) * (s / MAX_SPEED);
        ctx.fillRect(W / 2 + Math.min(0, sw), 24, Math.abs(sw), 4);
    }
    function onWheel(ev: WheelEvent): void {
        const d = wheelPx(ev);
        // 속도가 이미 끝까지 올랐으면 가로채지 않는다
        if (d === 0 || !canMove(d)) { return; }
        ev.preventDefault();
        wake();
        if (still) { flow += d; draw(); return; }
        extra = clamp(extra + d * SPEED_GAIN, -MAX_SPEED * 2, MAX_SPEED * 2);
    }
    cv.addEventListener('wheel', onWheel, { passive: false });
    let dragId = -1;
    let dragX = 0;
    let dragT = 0;
    let dragSpeed = 0;
    cv.addEventListener('pointerdown', function (ev: PointerEvent): void {
        wake();
        dragId = ev.pointerId;
        cv.setPointerCapture(ev.pointerId);
        dragX = toScene(ev)[0];
        dragT = ev.timeStamp;
        dragSpeed = 0;
    });
    cv.addEventListener('pointermove', function (ev: PointerEvent): void {
        if (ev.pointerId !== dragId) { return; }
        const sx = toScene(ev)[0];
        const dt = Math.max(1, ev.timeStamp - dragT) / 1000;
        // 왼쪽으로 끌면 글자가 왼쪽으로 — 흐름 값을 늘린다
        flow -= sx - dragX;
        dragSpeed = lerp(dragSpeed, -(sx - dragX) / dt, 0.4);
        dragX = sx;
        dragT = ev.timeStamp;
        if (still) { draw(); }
    });
    function endDrag(ev: PointerEvent): void {
        if (ev.pointerId !== dragId) { return; }
        dragId = -1;
        if (!still) { extra = clamp(dragSpeed - BASE_SPEED, -MAX_SPEED * 2, MAX_SPEED * 2); }
    }
    cv.addEventListener('pointerup', endDrag);
    cv.addEventListener('pointercancel', endDrag);
    cv.addEventListener('keydown', function (ev: KeyboardEvent): void {
        let d = 0;
        if (ev.key === 'ArrowRight') { d = 1; }
        else if (ev.key === 'ArrowLeft') { d = -1; }
        if (d === 0 || !canMove(d)) { return; }
        ev.preventDefault();
        wake();
        if (still) { flow += d * 60; draw(); return; }
        extra += d * 240;
    });
    if (pauseBtn) {
        pauseBtn.addEventListener('click', function (): void {
            wake();
            paused = !paused;
            if (paused) { extra = 0; }
            pauseBtn.setAttribute('aria-pressed', paused ? 'true' : 'false');
            say(paused ? TXT_PAUSE : TXT_FLOW);
        });
    }
    say(TXT_FLOW);

    let rafId = 0;
    let lastTs = -1;
    let acc = 0;
    let clock = 0;
    function frame(ts: number): void {
        if (lastTs < 0) { lastTs = ts; }
        // 탭이 숨었다 돌아와도 한 번에 100ms 까지만 따라잡는다 — 순간이동 대신 이어서 움직인다
        acc += Math.min(ts - lastTs, 100);
        lastTs = ts;
        let n = 0;
        while (acc >= FIXED_DT && n < 6) {
            clock += FIXED_DT;
            if (demo) { demoTick(clock); }
            step();
            acc -= FIXED_DT;
            n += 1;
        }
        draw();
        rafId = window.requestAnimationFrame(frame);
    }
    if (still) {
        settle();
        draw();
    } else {
        rafId = window.requestAnimationFrame(frame);
    }
    return function (): void {
        window.cancelAnimationFrame(rafId);
        window.removeEventListener('resize', onResize);
    };

  }, []);

  return (
    <div className={cx("hs") + " is-demo"} ref={rootRef}>
        <canvas className={cx("hs__canvas")} data-role="canvas" width={480} height={300} tabIndex={0} aria-label="물결 곡선을 따라 흐르는 글자들이 곡선 기울기만큼 돌아가고 빨라지면 물결이 커지는 리본"></canvas>
        <p className={cx("hs__status")} data-role="status" aria-live="off">흐르는 중</p>
        <div className={cx("hs__tools")}>
          <button className={cx("hs__btn")} data-role="btn" type="button" aria-pressed="false">멈춤</button>
        </div>
    </div>
  );
}