04Wave Bands Pushed One Way and Set Into Chevrons

<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="Wave bands pushed one way and set into chevrons"></canvas>
  <p class="hs__status" data-role="status" aria-live="off">Combing to the right</p>
  <div class="hs__tools">
    <button class="hs__btn" data-role="btn" type="button">Comb direction</button>
  </div>
</div>
</main>

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

.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: crosshair;
}

.hs__canvas:focus-visible {
  outline: 2px solid rgba(58, 48, 76, .9);
  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, 252, 244, .92);
  color: $subject-ink;
  font: inherit;
  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, 252, 244, .92);
  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(58, 48, 76, .9);
  outline-offset: 2px;
}

// 포인터로는 잉크를 다루고, 쓸어 넘기는 손가락 제스처는 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: #ffffff;
  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: crosshair;
}

.hs__canvas:focus-visible {
  outline: 2px solid rgba(58, 48, 76, 0.9);
  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, 252, 244, 0.92);
  color: #17141a;
  font: inherit;
  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, 252, 244, 0.92);
  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(58, 48, 76, 0.9);
  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;
    // 마블링 팔레트 — 종이 물면(PAPER) 위에 파스텔 잉크 결이 흐른다
    const PAPER = [252, 246, 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;
        }
    }
    // 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() {
        // 캔버스 내부 해상도는 480x300 고정, 배율은 devicePixelRatio 에 상한 2 를 둔다
        const dpr = Math.min(window.devicePixelRatio || 1, 2);
        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];
    }
    // ── 필드 버퍼(077 방식) — 항목이 정한 낮은 해상도 버퍼에 픽셀 값을 굽고 drawImage 로 부드럽게 확대한다
    const small = document.createElement('canvas');
    let sctx = null;
    let buf = null;
    let px = null;
    // 종이 결은 시간이 지나도 안 변한다 — 필드를 만들 때 한 번만 구워 두고 픽셀마다 꺼내 쓴다
    let grainF = new Float32Array(0);
    function initField(nw, nh) {
        small.width = nw;
        small.height = nh;
        const c = small.getContext('2d');
        if (!c) {
            return;
        }
        sctx = c;
        buf = c.createImageData(nw, nh);
        px = buf.data;
        grainF = new Float32Array(nw * nh);
        for (let y = 0; y < nh; y += 1) {
            for (let x = 0; x < nw; x += 1) {
                grainF[y * nw + x] = paperGrain(x * W / nw, y * H / nh);
            }
        }
    }
    function blitField(nw, nh) {
        if (!sctx || !buf) {
            return;
        }
        sctx.putImageData(buf, 0, 0);
        ctx.imageSmoothingEnabled = true;
        ctx.imageSmoothingQuality = 'high';
        ctx.drawImage(small, 0, 0, nw, nh, 0, 0, W, H);
    }
    // ── 결정적 값노이즈 — 난수 소스를 못 쓰므로 정수 해시로 같은 시드에 같은 값
    const SEED = 463;
    function hash1(n, seed) {
        let h = Math.imul(n ^ seed, 374761393);
        h = Math.imul(h ^ (h >>> 13), 1274126177);
        return ((h ^ (h >>> 16)) >>> 0) / 4294967296;
    }
    function hash2(x, y, seed) {
        return hash1((Math.imul(x, 73856093) ^ Math.imul(y, 19349663)) | 0, seed);
    }
    function fade(t) { return t * t * (3 - 2 * t); }
    function vnoise2(x, y, seed) {
        const xi = Math.floor(x), yi = Math.floor(y);
        const u = fade(x - xi), v = fade(y - yi);
        const a = hash2(xi, yi, seed), b = hash2(xi + 1, yi, seed);
        const c = hash2(xi, yi + 1, seed), d = hash2(xi + 1, yi + 1, seed);
        return lerp(lerp(a, b, u), lerp(c, d, u), v);
    }
    function fbm2(x, y, oct, seed) {
        let sum = 0, amp = 0.5, norm = 0, f = 1;
        for (let i = 0; i < oct; i += 1) {
            sum += vnoise2(x * f, y * f, seed + i * 131) * amp;
            norm += amp;
            amp *= 0.5;
            f *= 2;
        }
        return sum / norm;
    }
    // 종이 결 — 옅은 얼룩으로 종이가 느껴지게 하는 바닥 값(0~1)
    function paperGrain(x, y) {
        return fbm2(x * 0.021, y * 0.021, 3, 71);
    }
    // 04 빗질 결 — 어긋난 위상 사인파 합성 + 민 만큼 위상 표류 누적
    const WAVE_AMP = 26; // 사인파 진폭(px)
    const PHASE_DRIFT = 0.022; // 16ms 스텝마다 쌓이는 위상 표류(빗이 민 만큼)
    const CHEVRON_SKEW = 0.34; // 가로 위치에 비례해 띠를 비스듬히 누르는 기울기
    const BAND_PX = 13; // 물결 띠 한 줄 폭(px)
    const DEMO_LOOP = 3600;
    const FW = 240;
    const FH = 150;
    const TXT_R = 'Combing to the right';
    const TXT_L = 'Combing to the left';
    const TXT_SET = 'The wave bands set into a skew';
    const TXT_GUIDE = 'Arrow keys set the comb direction';
    let drift = 0; // 누적 위상 표류
    let dir = 1; // Comb direction
    let saidSet = false;
    let btnEl = null;
    function bandAt(x, y) {
        // 어긋난 위상 사인파 합성 — 줄마다 위상이 달라 물결, 가로 기울기가 셰브런을 만든다
        const tilt = CHEVRON_SKEW * (x - W / 2);
        const wave = WAVE_AMP * 0.5 * Math.sin(x * 0.011 + Math.sin(y * 0.028) * 1.15 + drift);
        const fine = WAVE_AMP * 0.22 * Math.sin(x * 0.0031 + y * 0.052 - drift * 0.6);
        return (y + tilt + wave + fine) / BAND_PX;
    }
    function draw() {
        if (!px || !sctx) {
            return;
        }
        const sx = FW / W, sy = FH / H;
        let i4 = 0;
        for (let y = 0; y < FH; y += 1) {
            const wy = y / sy;
            for (let x = 0; x < FW; x += 1) {
                const wx = x / sx;
                const g = grainF[y * FW + x];
                const base = mix(PAPER, INK, g * 0.07 + 0.015);
                const b = bandAt(wx, wy);
                const bi = Math.floor(b);
                const fr = b - bi;
                const tint = TINTS[Math.abs(bi + 40) % TINTS.length];
                let col = base;
                const k = smooth(1 - Math.abs(fr - 0.5) * 2);
                if (bi % 2 === 0) {
                    col = mix(base, tint, k * 0.5 + 0.1);
                    if (fr < 0.16) {
                        col = mix(col, INK, (0.16 - fr) * 2.2);
                    }
                }
                else {
                    col = mix(base, INK, 0.06 + k * 0.05);
                }
                px[i4] = col[0];
                px[i4 + 1] = col[1];
                px[i4 + 2] = col[2];
                px[i4 + 3] = 255;
                i4 += 4;
            }
        }
        blitField(FW, FH);
    }
    function settle() {
        drift = 3.2;
        say(TXT_SET);
    }
    function step() {
        drift += dir * PHASE_DRIFT;
        if (demo) {
            if (!saidSet && Math.abs(drift - 3.2) < 0.05) {
                saidSet = true;
                say(TXT_SET);
            }
            else if (!saidSet) {
                say(dir > 0 ? TXT_R : TXT_L);
            }
        }
    }
    function setDir(d) {
        dir = d;
        saidSet = false;
        if (still) {
            drift += d * 0.9;
            draw();
            return;
        }
        say(d > 0 ? TXT_R : TXT_L);
        if (btnEl) {
            btnEl.textContent = d > 0 ? 'Comb left' : 'Comb right';
        }
    }
    function demoTick(t) {
        if (crossed(t, 200, DEMO_LOOP)) {
            dir = 1;
            saidSet = false;
        }
        if (crossed(t, 1900, DEMO_LOOP)) {
            dir = -1;
        }
    }
    initField(FW, FH);
    btnEl = root.querySelector('[data-role="btn"]');
    if (btnEl) {
        btnEl.textContent = 'Comb left';
        btnEl.addEventListener('click', function () {
            wake();
            setDir(-dir);
        });
    }
    cv.addEventListener('pointerdown', function (ev) {
        wake();
        setDir(toScene(ev)[0] < W / 2 ? -1 : 1);
    });
    cv.addEventListener('keydown', function (ev) {
        const k = ev.key;
        if (k !== 'ArrowLeft' && k !== 'ArrowRight') {
            return;
        }
        ev.preventDefault();
        wake();
        setDir(k === 'ArrowRight' ? 1 : -1);
    });
    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);
    };
})();

// MblRakeWaveChevronBands - vanilla 판(04-mbl-rake-wave-chevron-bands) 의 React 포트. 같은 계산을 useEffect 안에서 돌린다.
import { useEffect, useRef } from "react";
import styles from "./MblRakeWaveChevronBands.module.scss";

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

export default function MblRakeWaveChevronBands() {
  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;
    // 마블링 팔레트 — 종이 물면(PAPER) 위에 파스텔 잉크 결이 흐른다
    const PAPER: RGB = [252, 246, 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; }
    }
    // 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 {
        // 캔버스 내부 해상도는 480x300 고정, 배율은 devicePixelRatio 에 상한 2 를 둔다
        const dpr = Math.min(window.devicePixelRatio || 1, 2);
        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];
    }
    // ── 필드 버퍼(077 방식) — 항목이 정한 낮은 해상도 버퍼에 픽셀 값을 굽고 drawImage 로 부드럽게 확대한다
    const small = document.createElement('canvas');
    let sctx: CanvasRenderingContext2D | null = null;
    let buf: ImageData | null = null;
    let px: Uint8ClampedArray | null = null;
    // 종이 결은 시간이 지나도 안 변한다 — 필드를 만들 때 한 번만 구워 두고 픽셀마다 꺼내 쓴다
    let grainF: Float32Array = new Float32Array(0);
    function initField(nw: number, nh: number): void {
        small.width = nw;
        small.height = nh;
        const c = small.getContext('2d');
        if (!c) { return; }
        sctx = c;
        buf = c.createImageData(nw, nh);
        px = buf.data;
        grainF = new Float32Array(nw * nh);
        for (let y = 0; y < nh; y += 1) {
            for (let x = 0; x < nw; x += 1) { grainF[y * nw + x] = paperGrain(x * W / nw, y * H / nh); }
        }
    }
    function blitField(nw: number, nh: number): void {
        if (!sctx || !buf) { return; }
        sctx.putImageData(buf, 0, 0);
        ctx.imageSmoothingEnabled = true;
        ctx.imageSmoothingQuality = 'high';
        ctx.drawImage(small, 0, 0, nw, nh, 0, 0, W, H);
    }
    // ── 결정적 값노이즈 — 난수 소스를 못 쓰므로 정수 해시로 같은 시드에 같은 값
    const SEED = 463;
    function hash1(n: number, seed: number): number {
        let h = Math.imul(n ^ seed, 374761393);
        h = Math.imul(h ^ (h >>> 13), 1274126177);
        return ((h ^ (h >>> 16)) >>> 0) / 4294967296;
    }
    function hash2(x: number, y: number, seed: number): number {
        return hash1((Math.imul(x, 73856093) ^ Math.imul(y, 19349663)) | 0, seed);
    }
    function fade(t: number): number { return t * t * (3 - 2 * t); }
    function vnoise2(x: number, y: number, seed: number): number {
        const xi = Math.floor(x), yi = Math.floor(y);
        const u = fade(x - xi), v = fade(y - yi);
        const a = hash2(xi, yi, seed), b = hash2(xi + 1, yi, seed);
        const c = hash2(xi, yi + 1, seed), d = hash2(xi + 1, yi + 1, seed);
        return lerp(lerp(a, b, u), lerp(c, d, u), v);
    }
    function fbm2(x: number, y: number, oct: number, seed: number): number {
        let sum = 0, amp = 0.5, norm = 0, f = 1;
        for (let i = 0; i < oct; i += 1) {
            sum += vnoise2(x * f, y * f, seed + i * 131) * amp;
            norm += amp;
            amp *= 0.5;
            f *= 2;
        }
        return sum / norm;
    }
    // 종이 결 — 옅은 얼룩으로 종이가 느껴지게 하는 바닥 값(0~1)
    function paperGrain(x: number, y: number): number {
        return fbm2(x * 0.021, y * 0.021, 3, 71);
    }
    // 04 빗질 결 — 어긋난 위상 사인파 합성 + 민 만큼 위상 표류 누적
    const WAVE_AMP = 26;        // 사인파 진폭(px)
    const PHASE_DRIFT = 0.022;  // 16ms 스텝마다 쌓이는 위상 표류(빗이 민 만큼)
    const CHEVRON_SKEW = 0.34;  // 가로 위치에 비례해 띠를 비스듬히 누르는 기울기
    const BAND_PX = 13;         // 물결 띠 한 줄 폭(px)
    const DEMO_LOOP = 3600;
    const FW = 240;
    const FH = 150;
    const TXT_R = '오른쪽으로 빗질하는 중';
    const TXT_L = '왼쪽으로 빗질하는 중';
    const TXT_SET = '물결 띠가 비스듬히 굳는다';
    const TXT_GUIDE = '화살표로 빗질 방향';
    let drift = 0;       // 누적 위상 표류
    let dir = 1;         // 빗질 방향
    let saidSet = false;
    let btnEl: HTMLButtonElement | null = null;
    function bandAt(x: number, y: number): number {
        // 어긋난 위상 사인파 합성 — 줄마다 위상이 달라 물결, 가로 기울기가 셰브런을 만든다
        const tilt = CHEVRON_SKEW * (x - W / 2);
        const wave = WAVE_AMP * 0.5 * Math.sin(x * 0.011 + Math.sin(y * 0.028) * 1.15 + drift);
        const fine = WAVE_AMP * 0.22 * Math.sin(x * 0.0031 + y * 0.052 - drift * 0.6);
        return (y + tilt + wave + fine) / BAND_PX;
    }
    function draw(): void {
        if (!px || !sctx) { return; }
        const sx = FW / W, sy = FH / H;
        let i4 = 0;
        for (let y = 0; y < FH; y += 1) {
            const wy = y / sy;
            for (let x = 0; x < FW; x += 1) {
                const wx = x / sx;
                const g = grainF[y * FW + x];
                const base = mix(PAPER, INK, g * 0.07 + 0.015);
                const b = bandAt(wx, wy);
                const bi = Math.floor(b);
                const fr = b - bi;
                const tint = TINTS[Math.abs(bi + 40) % TINTS.length];
                let col = base;
                const k = smooth(1 - Math.abs(fr - 0.5) * 2);
                if (bi % 2 === 0) {
                    col = mix(base, tint, k * 0.5 + 0.1);
                    if (fr < 0.16) { col = mix(col, INK, (0.16 - fr) * 2.2); }
                } else {
                    col = mix(base, INK, 0.06 + k * 0.05);
                }
                px[i4] = col[0]; px[i4 + 1] = col[1]; px[i4 + 2] = col[2]; px[i4 + 3] = 255;
                i4 += 4;
            }
        }
        blitField(FW, FH);
    }
    function settle(): void {
        drift = 3.2;
        say(TXT_SET);
    }
    function step(): void {
        drift += dir * PHASE_DRIFT;
        if (demo) {
            if (!saidSet && Math.abs(drift - 3.2) < 0.05) { saidSet = true; say(TXT_SET); }
            else if (!saidSet) { say(dir > 0 ? TXT_R : TXT_L); }
        }
    }
    function setDir(d: number): void {
        dir = d;
        saidSet = false;
        if (still) { drift += d * 0.9; draw(); return; }
        say(d > 0 ? TXT_R : TXT_L);
        if (btnEl) { btnEl.textContent = d > 0 ? '왼쪽으로 빗질' : '오른쪽으로 빗질'; }
    }
    function demoTick(t: number): void {
        if (crossed(t, 200, DEMO_LOOP)) { dir = 1; saidSet = false; }
        if (crossed(t, 1900, DEMO_LOOP)) { dir = -1; }
    }
    initField(FW, FH);
    btnEl = root.querySelector('[data-role="btn"]') as HTMLButtonElement | null;
    if (btnEl) {
        btnEl.textContent = '왼쪽으로 빗질';
        btnEl.addEventListener('click', function (): void {
            wake();
            setDir(-dir);
        });
    }
    cv.addEventListener('pointerdown', function (ev: PointerEvent): void {
        wake();
        setDir(toScene(ev)[0] < W / 2 ? -1 : 1);
    });
    cv.addEventListener('keydown', function (ev: KeyboardEvent): void {
        const k = ev.key;
        if (k !== 'ArrowLeft' && k !== 'ArrowRight') { return; }
        ev.preventDefault();
        wake();
        setDir(k === 'ArrowRight' ? 1 : -1);
    });

    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="한 방향으로 밀린 물결 띠가 비스듬히 굳는 빗질 결"></canvas>
        <p className={cx("hs__status")} data-role="status" aria-live="off">오른쪽으로 빗질하는 중</p>
        <div className={cx("hs__tools")}>
          <button className={cx("hs__btn")} data-role="btn" type="button">빗질 방향</button>
        </div>
    </div>
  );
}