08트랙 양 끝에 다가간 카드가 어안 렌즈처럼 휘어 작아지고 가운데에서는 평평하게 펴지는 가장자리 렌즈

<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="아이콘 줄이 화면 가장자리로 갈수록 어안 렌즈처럼 작아지고 휘어 보이는 장면"></canvas>
  <p class="hs__status" data-role="status" aria-live="off">렌즈 켬</p>
  <div class="hs__tools">
    <button class="hs__btn" data-role="btn" type="button" aria-pressed="false">렌즈 끄기</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 TILE_N = 16;
    const TILE_W = 92;
    const TILE_H = 116;
    const TILE_GAP = 14;
    const PITCH = TILE_W + TILE_GAP;
    const PAD = 24;
    const SRC_W = PAD * 2 + TILE_N * PITCH - TILE_GAP;
    const CY = 136;
    const LENS_K = 0.35;
    const LENS_P = 2;
    const BEND = 26;
    const K_LERP = 0.12;
    const S_LERP = 0.1;
    const DEMO_LOOP = 4400;
    const TXT_FLOW = '렌즈 아래로 흐르는 중';
    const TXT_ON = '렌즈 켬';
    const TXT_OFF = '렌즈 끔';
    const lensBtn = root.querySelector('[data-role="btn"]');
    // 화면 가로 위치 u(−1~1) → 원본 표본 위치 s. s = u·(1 + K·|u|^P) — 가장자리일수록 원본을 더 많이 눌러 담는다
    function lensSample(u, k) { return u * (1 + k * Math.pow(Math.abs(u), LENS_P)); }
    // 그 자리의 확대율 du/ds — 가운데 1, 가장자리 1/(1 + K·(P+1))
    function lensScale(u, k) { return 1 / (1 + k * (LENS_P + 1) * Math.pow(Math.abs(u), LENS_P)); }
    // 렌즈 세기 k 일 때 화면 반쪽(240px)이 담는 원본 폭의 반
    function halfSpan(k) { return (W / 2) * (1 + k); }
    function maxScroll(k) { return SRC_W - 2 * halfSpan(k); }
    // 원본 — 평평한 아이콘 줄을 한 번만 그려 픽셀을 읽어 둔다(getImageData 는 시작 때 1회)
    const srcCanvas = document.createElement('canvas');
    srcCanvas.width = SRC_W;
    srcCanvas.height = H;
    const sctxRaw = srcCanvas.getContext('2d');
    const bufCanvas = document.createElement('canvas');
    bufCanvas.width = W;
    bufCanvas.height = H;
    const bctxRaw = bufCanvas.getContext('2d');
    if (!sctxRaw || !bctxRaw) {
        return;
    }
    const sctx = sctxRaw;
    const bctx = bctxRaw;
    sctx.fillStyle = rgba(BG, 1);
    sctx.fillRect(0, 0, SRC_W, H);
    // 바탕 격자 — 렌즈가 휘는 모양이 선으로 드러난다
    sctx.fillStyle = rgba(mix(BG, LILAC, 0.16), 1);
    for (let gx = 0; gx < SRC_W; gx += 24) {
        sctx.fillRect(gx, 0, 1, H);
    }
    for (let gy = 16; gy < H; gy += 24) {
        sctx.fillRect(0, gy, SRC_W, 1);
    }
    for (let i = 0; i < TILE_N; i += 1) {
        drawCard(sctx, PAD + i * PITCH, CY - TILE_H / 2, TILE_W, TILE_H, i, 1);
    }
    const src = sctx.getImageData(0, 0, SRC_W, H).data;
    const out = bctx.createImageData(W, H);
    const dst = out.data;
    const bgR = BG[0];
    const bgG = BG[1];
    const bgB = BG[2];
    let kNow = LENS_K;
    let kTarget = LENS_K;
    let target = 0;
    let scroll = 0;
    let dirty = true;
    let flowing = false;
    // 한 장 다시 그리기 — 화면 픽셀마다 렌즈 곡선으로 원본 위치를 거꾸로 찾아 그 색을 가져온다
    function remap() {
        const center = scroll + halfSpan(kNow);
        for (let x = 0; x < W; x += 1) {
            const u = (x + 0.5 - W / 2) / (W / 2);
            const sx = Math.round(center + lensSample(u, kNow) * (W / 2));
            const sc = lensScale(u, kNow);
            const sag = BEND * u * u * (kNow / LENS_K);
            for (let y = 0; y < H; y += 1) {
                const sy = Math.round(CY + (y - CY - sag) / sc);
                const o = (y * W + x) * 4;
                if (sx < 0 || sx >= SRC_W || sy < 0 || sy >= H) {
                    dst[o] = bgR;
                    dst[o + 1] = bgG;
                    dst[o + 2] = bgB;
                    dst[o + 3] = 255;
                    continue;
                }
                const i = (sy * SRC_W + sx) * 4;
                dst[o] = src[i];
                dst[o + 1] = src[i + 1];
                dst[o + 2] = src[i + 2];
                dst[o + 3] = 255;
            }
        }
        bctx.putImageData(out, 0, 0);
        dirty = false;
    }
    function step() {
        const ps = scroll;
        const pk = kNow;
        kNow += (kTarget - kNow) * K_LERP;
        if (Math.abs(kTarget - kNow) < 0.001) {
            kNow = kTarget;
        }
        target = clamp(target, 0, maxScroll(kNow));
        scroll += (target - scroll) * S_LERP;
        if (Math.abs(target - scroll) < 0.05) {
            scroll = target;
        }
        if (scroll !== ps || kNow !== pk) {
            dirty = true;
        }
        const now = Math.abs(scroll - ps) > 0.05;
        if (now && !flowing) {
            say(TXT_FLOW);
        }
        flowing = now;
    }
    function settle() {
        kNow = kTarget;
        scroll = clamp(target, 0, maxScroll(kNow));
        dirty = true;
    }
    function demoTick(t) {
        if (crossed(t, 200, DEMO_LOOP)) {
            target = 520;
        }
        if (crossed(t, 1350, DEMO_LOOP)) {
            target = 120;
        }
    }
    function draw() {
        if (dirty) {
            remap();
        }
        ctx.drawImage(bufCanvas, 0, 0, W, H);
        // 가장자리 그늘 — 렌즈 바깥이 둥글게 꺼지는 느낌
        const g = ctx.createLinearGradient(0, 0, W, 0);
        g.addColorStop(0, rgba(BG, 0.55 * kNow / LENS_K));
        g.addColorStop(0.12, rgba(BG, 0));
        g.addColorStop(0.88, rgba(BG, 0));
        g.addColorStop(1, rgba(BG, 0.55 * kNow / LENS_K));
        ctx.fillStyle = g;
        ctx.fillRect(0, 0, W, H);
    }
    function canMove(d) { return d > 0 ? target < maxScroll(kNow) - 0.5 : target > 0.5; }
    function moveTo(p) {
        target = clamp(p, 0, maxScroll(kNow));
        if (still) {
            settle();
            draw();
        }
    }
    function onWheel(ev) {
        const d = wheelPx(ev);
        if (d === 0 || !canMove(d)) {
            return;
        }
        ev.preventDefault();
        wake();
        moveTo(target + d);
    }
    cv.addEventListener('wheel', onWheel, { passive: false });
    let dragId = -1;
    let dragX = 0;
    cv.addEventListener('pointerdown', function (ev) {
        wake();
        dragId = ev.pointerId;
        cv.setPointerCapture(ev.pointerId);
        dragX = toScene(ev)[0];
    });
    cv.addEventListener('pointermove', function (ev) {
        if (ev.pointerId !== dragId) {
            return;
        }
        const sx = toScene(ev)[0];
        moveTo(target - (sx - dragX));
        dragX = sx;
    });
    function endDrag(ev) { if (ev.pointerId === dragId) {
        dragId = -1;
    } }
    cv.addEventListener('pointerup', endDrag);
    cv.addEventListener('pointercancel', endDrag);
    cv.addEventListener('keydown', function (ev) {
        let goal = NaN;
        if (ev.key === 'ArrowRight') {
            goal = target + PITCH;
        }
        else if (ev.key === 'ArrowLeft') {
            goal = target - PITCH;
        }
        else if (ev.key === 'Home') {
            goal = 0;
        }
        else if (ev.key === 'End') {
            goal = maxScroll(kNow);
        }
        if (Number.isNaN(goal) || !canMove(goal - target)) {
            return;
        }
        ev.preventDefault();
        wake();
        moveTo(goal);
    });
    if (lensBtn) {
        lensBtn.addEventListener('click', function () {
            wake();
            const off = kTarget > 0;
            kTarget = off ? 0 : LENS_K;
            lensBtn.setAttribute('aria-pressed', off ? 'true' : 'false');
            say(off ? TXT_OFF : TXT_ON);
            if (still) {
                settle();
                draw();
            }
        });
    }
    say(TXT_ON);
    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);
    };
})();

// HscEdgeFisheyePixelRemap - vanilla 판(08-hsc-edge-fisheye-pixel-remap) 의 React 포트. 같은 계산을 useEffect 안에서 돌린다.
import { useEffect, useRef } from "react";
import styles from "./HscEdgeFisheyePixelRemap.module.scss";

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

export default function HscEdgeFisheyePixelRemap() {
  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 TILE_N = 16;
    const TILE_W = 92;
    const TILE_H = 116;
    const TILE_GAP = 14;
    const PITCH = TILE_W + TILE_GAP;
    const PAD = 24;
    const SRC_W = PAD * 2 + TILE_N * PITCH - TILE_GAP;
    const CY = 136;
    const LENS_K = 0.35;
    const LENS_P = 2;
    const BEND = 26;
    const K_LERP = 0.12;
    const S_LERP = 0.1;
    const DEMO_LOOP = 4400;
    const TXT_FLOW = '렌즈 아래로 흐르는 중';
    const TXT_ON = '렌즈 켬';
    const TXT_OFF = '렌즈 끔';
    const lensBtn = root.querySelector('[data-role="btn"]') as HTMLButtonElement | null;
    // 화면 가로 위치 u(−1~1) → 원본 표본 위치 s. s = u·(1 + K·|u|^P) — 가장자리일수록 원본을 더 많이 눌러 담는다
    function lensSample(u: number, k: number): number { return u * (1 + k * Math.pow(Math.abs(u), LENS_P)); }
    // 그 자리의 확대율 du/ds — 가운데 1, 가장자리 1/(1 + K·(P+1))
    function lensScale(u: number, k: number): number { return 1 / (1 + k * (LENS_P + 1) * Math.pow(Math.abs(u), LENS_P)); }
    // 렌즈 세기 k 일 때 화면 반쪽(240px)이 담는 원본 폭의 반
    function halfSpan(k: number): number { return (W / 2) * (1 + k); }
    function maxScroll(k: number): number { return SRC_W - 2 * halfSpan(k); }
    // 원본 — 평평한 아이콘 줄을 한 번만 그려 픽셀을 읽어 둔다(getImageData 는 시작 때 1회)
    const srcCanvas = document.createElement('canvas');
    srcCanvas.width = SRC_W;
    srcCanvas.height = H;
    const sctxRaw = srcCanvas.getContext('2d');
    const bufCanvas = document.createElement('canvas');
    bufCanvas.width = W;
    bufCanvas.height = H;
    const bctxRaw = bufCanvas.getContext('2d');
    if (!sctxRaw || !bctxRaw) { return; }
    const sctx: CanvasRenderingContext2D = sctxRaw;
    const bctx: CanvasRenderingContext2D = bctxRaw;
    sctx.fillStyle = rgba(BG, 1);
    sctx.fillRect(0, 0, SRC_W, H);
    // 바탕 격자 — 렌즈가 휘는 모양이 선으로 드러난다
    sctx.fillStyle = rgba(mix(BG, LILAC, 0.16), 1);
    for (let gx = 0; gx < SRC_W; gx += 24) { sctx.fillRect(gx, 0, 1, H); }
    for (let gy = 16; gy < H; gy += 24) { sctx.fillRect(0, gy, SRC_W, 1); }
    for (let i = 0; i < TILE_N; i += 1) {
        drawCard(sctx, PAD + i * PITCH, CY - TILE_H / 2, TILE_W, TILE_H, i, 1);
    }
    const src = sctx.getImageData(0, 0, SRC_W, H).data;
    const out = bctx.createImageData(W, H);
    const dst = out.data;
    const bgR = BG[0];
    const bgG = BG[1];
    const bgB = BG[2];
    let kNow = LENS_K;
    let kTarget = LENS_K;
    let target = 0;
    let scroll = 0;
    let dirty = true;
    let flowing = false;
    // 한 장 다시 그리기 — 화면 픽셀마다 렌즈 곡선으로 원본 위치를 거꾸로 찾아 그 색을 가져온다
    function remap(): void {
        const center = scroll + halfSpan(kNow);
        for (let x = 0; x < W; x += 1) {
            const u = (x + 0.5 - W / 2) / (W / 2);
            const sx = Math.round(center + lensSample(u, kNow) * (W / 2));
            const sc = lensScale(u, kNow);
            const sag = BEND * u * u * (kNow / LENS_K);
            for (let y = 0; y < H; y += 1) {
                const sy = Math.round(CY + (y - CY - sag) / sc);
                const o = (y * W + x) * 4;
                if (sx < 0 || sx >= SRC_W || sy < 0 || sy >= H) {
                    dst[o] = bgR; dst[o + 1] = bgG; dst[o + 2] = bgB; dst[o + 3] = 255;
                    continue;
                }
                const i = (sy * SRC_W + sx) * 4;
                dst[o] = src[i]; dst[o + 1] = src[i + 1]; dst[o + 2] = src[i + 2]; dst[o + 3] = 255;
            }
        }
        bctx.putImageData(out, 0, 0);
        dirty = false;
    }
    function step(): void {
        const ps = scroll;
        const pk = kNow;
        kNow += (kTarget - kNow) * K_LERP;
        if (Math.abs(kTarget - kNow) < 0.001) { kNow = kTarget; }
        target = clamp(target, 0, maxScroll(kNow));
        scroll += (target - scroll) * S_LERP;
        if (Math.abs(target - scroll) < 0.05) { scroll = target; }
        if (scroll !== ps || kNow !== pk) { dirty = true; }
        const now = Math.abs(scroll - ps) > 0.05;
        if (now && !flowing) { say(TXT_FLOW); }
        flowing = now;
    }
    function settle(): void {
        kNow = kTarget;
        scroll = clamp(target, 0, maxScroll(kNow));
        dirty = true;
    }
    function demoTick(t: number): void {
        if (crossed(t, 200, DEMO_LOOP)) { target = 520; }
        if (crossed(t, 1350, DEMO_LOOP)) { target = 120; }
    }
    function draw(): void {
        if (dirty) { remap(); }
        ctx.drawImage(bufCanvas, 0, 0, W, H);
        // 가장자리 그늘 — 렌즈 바깥이 둥글게 꺼지는 느낌
        const g = ctx.createLinearGradient(0, 0, W, 0);
        g.addColorStop(0, rgba(BG, 0.55 * kNow / LENS_K));
        g.addColorStop(0.12, rgba(BG, 0));
        g.addColorStop(0.88, rgba(BG, 0));
        g.addColorStop(1, rgba(BG, 0.55 * kNow / LENS_K));
        ctx.fillStyle = g;
        ctx.fillRect(0, 0, W, H);
    }
    function canMove(d: number): boolean { return d > 0 ? target < maxScroll(kNow) - 0.5 : target > 0.5; }
    function moveTo(p: number): void {
        target = clamp(p, 0, maxScroll(kNow));
        if (still) { settle(); draw(); }
    }
    function onWheel(ev: WheelEvent): void {
        const d = wheelPx(ev);
        if (d === 0 || !canMove(d)) { return; }
        ev.preventDefault();
        wake();
        moveTo(target + d);
    }
    cv.addEventListener('wheel', onWheel, { passive: false });
    let dragId = -1;
    let dragX = 0;
    cv.addEventListener('pointerdown', function (ev: PointerEvent): void {
        wake();
        dragId = ev.pointerId;
        cv.setPointerCapture(ev.pointerId);
        dragX = toScene(ev)[0];
    });
    cv.addEventListener('pointermove', function (ev: PointerEvent): void {
        if (ev.pointerId !== dragId) { return; }
        const sx = toScene(ev)[0];
        moveTo(target - (sx - dragX));
        dragX = sx;
    });
    function endDrag(ev: PointerEvent): void { if (ev.pointerId === dragId) { dragId = -1; } }
    cv.addEventListener('pointerup', endDrag);
    cv.addEventListener('pointercancel', endDrag);
    cv.addEventListener('keydown', function (ev: KeyboardEvent): void {
        let goal = NaN;
        if (ev.key === 'ArrowRight') { goal = target + PITCH; }
        else if (ev.key === 'ArrowLeft') { goal = target - PITCH; }
        else if (ev.key === 'Home') { goal = 0; }
        else if (ev.key === 'End') { goal = maxScroll(kNow); }
        if (Number.isNaN(goal) || !canMove(goal - target)) { return; }
        ev.preventDefault();
        wake();
        moveTo(goal);
    });
    if (lensBtn) {
        lensBtn.addEventListener('click', function (): void {
            wake();
            const off = kTarget > 0;
            kTarget = off ? 0 : LENS_K;
            lensBtn.setAttribute('aria-pressed', off ? 'true' : 'false');
            say(off ? TXT_OFF : TXT_ON);
            if (still) { settle(); draw(); }
        });
    }
    say(TXT_ON);

    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="아이콘 줄이 화면 가장자리로 갈수록 어안 렌즈처럼 작아지고 휘어 보이는 장면"></canvas>
        <p className={cx("hs__status")} data-role="status" aria-live="off">렌즈 켬</p>
        <div className={cx("hs__tools")}>
          <button className={cx("hs__btn")} data-role="btn" type="button" aria-pressed="false">렌즈 끄기</button>
        </div>
    </div>
  );
}