07An Endless Brick Wall Whose Columns Drift in Opposite Directions

<main class="stage">
<div class="mr is-demo" id="mr" data-demo="1">
  <div class="mr__bar">
    <div class="mr__btns"><button class="mr__btn" type="button" data-r="slow" aria-label="Slower">−</button><button class="mr__btn" type="button" data-r="fast" aria-label="Faster">+</button><button class="mr__btn" type="button" data-r="pause" aria-pressed="false">Pause</button></div>
    <p class="mr__live" data-r="live" aria-live="off" aria-atomic="true"><span class="mr__k">Speed</span> <b data-r="speed">1.0</b>×</p>
  </div>
  <div class="mr__wall" data-r="wall"></div>
</div>
</main>

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

// 핵심: 열마다 깊이 비율 속도로 번갈아 흐르고 한 열 높이만큼 흐르면 되감는다. 배치는 JS 가 계산하고 CSS 는 모양만 맡는다.

@include stage($stage-ink);

$fg: $subject-cream;
$mute: $tick-mute;
$btn-bg: rgba($subject-cream, .14);
$wall-bg: rgba($subject-cream, .06);
$focus: $subject-pink;
$on: $stage-ink;

.mr {
  position: relative;
  box-sizing: border-box;
  width: min(100%, 440px);
  height: min(252px, calc(100vh - 2 * clamp(8px, 4vw, 24px)));
  display: flex;
  flex-direction: column;
  gap: $sp-2;
  color: $fg;
  font-size: 12px;
  line-height: 16px;
  font-weight: 600;
  user-select: none;
}
.mr b { font-weight: 800; font-variant-numeric: tabular-nums; }
.mr__bar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: $sp-2;
  min-height: 28px;
}
.mr__btns {
  display: flex;
  flex-wrap: wrap;
  gap: $sp-1;
}
.mr__btn {
  box-sizing: border-box;
  min-width: 28px;
  height: 28px;
  padding: 0 $sp-3;
  border: 0;
  border-radius: $r-pill;
  background: $btn-bg;
  color: $fg;
  font-size: 12px;
  line-height: 16px;
  font-weight: 700;
  white-space: nowrap;
  cursor: pointer;
}
.mr__btn[aria-pressed="true"] { background: $fg; color: $on; }
.mr__btn:focus-visible { outline: 3px solid $focus; outline-offset: 2px; }
.mr__live { margin: 0; color: $mute; white-space: nowrap; }
.mr__live b { color: $fg; }
.mr__wall {
  position: relative;
  flex: 1 1 auto;
  min-height: 0;
  overflow: hidden;
  border-radius: $r-card;
  background: $wall-bg;
}
.mr__card {
  position: absolute;
  left: 0;
  top: 0;
  box-sizing: border-box;
  overflow: hidden;
  border-radius: $r-sm;
  background: linear-gradient(150deg, $subject-lilac, $subject-pink);
  color: $subject-ink;
  will-change: transform;
  box-shadow: 0 calc(2px + var(--lift, 0) * 10px) calc(6px + var(--lift, 0) * 14px) rgba($subject-ink, .22);
}
.mr__card::after {
  content: "";
  position: absolute;
  inset: 0;
  background: linear-gradient(135deg, rgba($stage-paper, .45), rgba($stage-paper, 0) 55%);
  pointer-events: none;
}
.mr__card[data-c="1"] { background: linear-gradient(150deg, $subject-sky, $subject-mint); }
.mr__card[data-c="2"] { background: linear-gradient(150deg, $subject-mint, $subject-lilac); }
.mr__card[data-c="3"] { background: linear-gradient(150deg, $subject-sky, $subject-lilac); }
.mr__card[data-c="4"] { background: linear-gradient(150deg, $subject-pink, $subject-lilac); }
.mr__card[data-c="5"] { background: linear-gradient(150deg, $subject-mint, $subject-sky); }
.mr__card i {
  position: absolute;
  left: $sp-2;
  top: $sp-1;
  font-style: normal;
  font-size: 12px;
  line-height: 16px;
  font-weight: 800;
  z-index: 1;
  opacity: .85;
}
.mr__col {
  position: absolute;
  top: 0;
  will-change: transform;
}
.mr__mark {
  position: absolute;
  left: 0;
  top: 0;
  height: $sp-1;
  border-radius: $r-pill;
  background: rgba($fg, .3);
  z-index: 3;
  pointer-events: none;
}
.mr__mark[data-low] { background: $subject-mint; }
@media (prefers-reduced-motion: reduce) {
  .mr__cursor, .mr__ring { display: none; }
  .mr__card { will-change: auto; }
}

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);
}

.mr {
  position: relative;
  box-sizing: border-box;
  width: min(100%, 440px);
  height: min(252px, 100vh - 2 * clamp(8px, 4vw, 24px));
  display: flex;
  flex-direction: column;
  gap: 8px;
  color: #fff7e6;
  font-size: 12px;
  line-height: 16px;
  font-weight: 600;
  user-select: none;
}

.mr b {
  font-weight: 800;
  font-variant-numeric: tabular-nums;
}

.mr__bar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
  min-height: 28px;
}

.mr__btns {
  display: flex;
  flex-wrap: wrap;
  gap: 4px;
}

.mr__btn {
  box-sizing: border-box;
  min-width: 28px;
  height: 28px;
  padding: 0 12px;
  border: 0;
  border-radius: 999px;
  background: rgba(255, 247, 230, 0.14);
  color: #fff7e6;
  font-size: 12px;
  line-height: 16px;
  font-weight: 700;
  white-space: nowrap;
  cursor: pointer;
}

.mr__btn[aria-pressed=true] {
  background: #fff7e6;
  color: #17141a;
}

.mr__btn:focus-visible {
  outline: 3px solid #ff9ebb;
  outline-offset: 2px;
}

.mr__live {
  margin: 0;
  color: #9a93a6;
  white-space: nowrap;
}

.mr__live b {
  color: #fff7e6;
}

.mr__wall {
  position: relative;
  flex: 1 1 auto;
  min-height: 0;
  overflow: hidden;
  border-radius: 16px;
  background: rgba(255, 247, 230, 0.06);
}

.mr__card {
  position: absolute;
  left: 0;
  top: 0;
  box-sizing: border-box;
  overflow: hidden;
  border-radius: 8px;
  background: linear-gradient(150deg, #b9a0ff, #ff9ebb);
  color: #17141a;
  will-change: transform;
  box-shadow: 0 calc(2px + var(--lift, 0) * 10px) calc(6px + var(--lift, 0) * 14px) rgba(23, 20, 26, 0.22);
}

.mr__card::after {
  content: "";
  position: absolute;
  inset: 0;
  background: linear-gradient(135deg, rgba(255, 255, 255, 0.45), rgba(255, 255, 255, 0) 55%);
  pointer-events: none;
}

.mr__card[data-c="1"] {
  background: linear-gradient(150deg, #6ec8ff, #4cd4a6);
}

.mr__card[data-c="2"] {
  background: linear-gradient(150deg, #4cd4a6, #b9a0ff);
}

.mr__card[data-c="3"] {
  background: linear-gradient(150deg, #6ec8ff, #b9a0ff);
}

.mr__card[data-c="4"] {
  background: linear-gradient(150deg, #ff9ebb, #b9a0ff);
}

.mr__card[data-c="5"] {
  background: linear-gradient(150deg, #4cd4a6, #6ec8ff);
}

.mr__card i {
  position: absolute;
  left: 8px;
  top: 4px;
  font-style: normal;
  font-size: 12px;
  line-height: 16px;
  font-weight: 800;
  z-index: 1;
  opacity: 0.85;
}

.mr__col {
  position: absolute;
  top: 0;
  will-change: transform;
}

.mr__mark {
  position: absolute;
  left: 0;
  top: 0;
  height: 4px;
  border-radius: 999px;
  background: rgba(255, 247, 230, 0.3);
  z-index: 3;
  pointer-events: none;
}

.mr__mark[data-low] {
  background: #4cd4a6;
}

@media (prefers-reduced-motion: reduce) {
  .mr__cursor, .mr__ring {
    display: none;
  }
  .mr__card {
    will-change: auto;
  }
}

(function () {
    const root = document.getElementById("mr");
    const CLS = { card: "mr__card", col: "mr__col" };
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let demo = !reduce;
    let raf = 0;
    let last = -1;
    let ready = false;
    const offs = [];
    function q(sel) {
        return root.querySelector(sel);
    }
    const wall = q("[data-r=wall]");
    const live = q("[data-r=live]");
    function clamp(v, lo, hi) {
        return Math.max(lo, Math.min(hi, v));
    }
    function makeRng(seed) {
        let s = seed >>> 0;
        return function () {
            s = (Math.imul(s, 1664525) + 1013904223) >>> 0;
            return s / 4294967296;
        };
    }
    function on(el, type, fn) {
        el.addEventListener(type, fn);
        offs.push(function () {
            el.removeEventListener(type, fn);
        });
    }
    function stopDemo() {
        if (!demo) return;
        demo = false;
        root.removeAttribute("data-demo");
        root.classList.remove("is-demo");
        live.setAttribute("aria-live", "polite");
    }
    if (reduce) live.setAttribute("aria-live", "polite");
    // Cards: 시드 LCG 로 비율을 뽑는다. 이미지 파일은 없고 그라디언트와 번호만 있다.
    function makeCards(n, seed, lo, hi) {
        const rng = makeRng(seed);
        const list = [];
        for (let i = 0; i < n; i += 1) {
            const el = document.createElement("div");
            el.className = CLS.card;
            el.setAttribute("data-c", String(i % 6));
            el.innerHTML = "<i>" + (i + 1) + "</i>";
            wall.appendChild(el);
            list.push({
                el: el, ratio: lo + rng() * (hi - lo), cat: Math.floor(rng() * 3),
                x: 0, y: 0, w: 0, h: 0, tx: 0, ty: 0, tw: 0, th: 0,
                s: 1, ds: 1, o: 1, dop: 1, vx: 0, vy: 0,
                ox: 0, oy: 0, osx: 0, osy: 0, ovx: 0, ovy: 0, ovsx: 0, ovsy: 0,
                fx: 0, fy: 0, fs: 1, fo: 1, t0: 0, sq: 0, rest: 0, wait: 0
            });
        }
        return list;
    }
    function colW(cols, gap) {
        return (wall.clientWidth - gap * (cols - 1)) / cols;
    }
    // 최단 Columns 배치: 카드를 순서대로 읽으며 지금 가장 낮은 Columns 끝에 얹고 그 Columns 높이에 Cards 높이와 간격을 더한다.
    function pack(hs, cols, cw, gap) {
        const colH = [];
        for (let k = 0; k < cols; k += 1) colH.push(0);
        const out = [];
        for (let i = 0; i < hs.length; i += 1) {
            let best = 0;
            for (let k = 1; k < cols; k += 1) {
                if (colH[k] < colH[best] - 0.5) best = k;
            }
            out.push({ x: best * (cw + gap), y: colH[best] });
            colH[best] += hs[i] + gap;
        }
        return out;
    }
    function put(c, x, y, sx, sy) {
        const st = c.el.style;
        st.width = c.w.toFixed(1) + "px";
        st.height = c.h.toFixed(1) + "px";
        st.transform = "translate3d(" + x.toFixed(2) + "px," + y.toFixed(2) + "px,0) scale(" + sx.toFixed(3) + "," + sy.toFixed(3) + ")";
    }
    function frame(ts) {
        const dt = last < 0 ? 0.016 : Math.min(0.05, (ts - last) / 1000);
        last = ts;
        if (demo) script(ts);
        step(dt, ts);
        render();
        raf = requestAnimationFrame(frame);
    }
    const ro = new ResizeObserver(function () {
        relayout();
    });
    ro.observe(root);

    // 기법: 열마다 속도에 깊이 비율을 곱하고 방향을 번갈아 정한다. Columns 내용을 두 번 이상 이어 붙이고 위치를 한 Columns 높이로 나눈 나머지로 되감아 이음새를 숨긴다.
    const COLUMNS = 4;
    const GAP = 8;
    const SPEED = 64;
    const DEPTH = [1, 0.62, 1.3, 0.8];
    const PER = 5;
    const SEED = 3;
    const rng = makeRng(SEED);
    const ratios = [];
    const pos = [0, 0, 0, 0];
    const spans = [1, 1, 1, 1];
    const cols = [];
    const speedEl = q("[data-r=speed]");
    const pauseBtn = q("[data-r=pause]");
    let mult = 1;
    let paused = false;
    for (let i = 0; i < COLUMNS * PER; i += 1) ratios.push(0.4 + rng() * 0.6);
    function build() {
        while (wall.firstChild) wall.removeChild(wall.firstChild);
        cols.length = 0;
        const cw = colW(COLUMNS, GAP);
        for (let k = 0; k < COLUMNS; k += 1) {
            const col = document.createElement("div");
            col.className = CLS.col;
            col.style.left = (k * (cw + GAP)).toFixed(1) + "px";
            col.style.width = cw.toFixed(1) + "px";
            let total = 0;
            for (let i = 0; i < PER; i += 1) total += ratios[k * PER + i] * cw + GAP;
            const copies = Math.ceil((total + wall.clientHeight) / total);
            for (let n = 0; n < copies; n += 1) {
                let y = n * total;
                for (let i = 0; i < PER; i += 1) {
                    const h = ratios[k * PER + i] * cw;
                    const el = document.createElement("div");
                    el.className = CLS.card;
                    el.setAttribute("data-c", String((k * PER + i) % 6));
                    el.innerHTML = "<i>" + (k * PER + i + 1) + "</i>";
                    if (n > 0) el.setAttribute("aria-hidden", "true");
                    el.style.width = cw.toFixed(1) + "px";
                    el.style.height = h.toFixed(1) + "px";
                    el.style.transform = "translate3d(0," + y.toFixed(1) + "px,0)";
                    col.appendChild(el);
                    y += h + GAP;
                }
            }
            spans[k] = total;
            cols.push(col);
            wall.appendChild(col);
        }
    }
    function relayout() {
        build();
        for (let k = 0; k < COLUMNS; k += 1) pos[k] = pos[k] % spans[k];
        ready = true;
        speedEl.textContent = mult.toFixed(1);
        render();
    }
    function script(ts) {
        // 시연은 기본 속도로 계속 흐른다.
    }
    function step(dt, ts) {
        if (paused) return;
        for (let k = 0; k < COLUMNS; k += 1) {
            const dir = k % 2 === 0 ? 1 : -1;
            const next = pos[k] + dir * SPEED * DEPTH[k] * mult * dt;
            pos[k] = ((next % spans[k]) + spans[k]) % spans[k];
        }
    }
    function render() {
        for (let k = 0; k < cols.length; k += 1) {
            cols[k].style.transform = "translate3d(0," + (-pos[k]).toFixed(1) + "px,0)";
        }
    }
    function bump() {
        // 움직임 줄이기에서는 흐르지 않으므로 누를 때마다 한 칸 밀어서 바뀐 결과를 바로 보여 준다.
        if (!reduce) return;
        for (let k = 0; k < COLUMNS; k += 1) {
            pos[k] = (pos[k] + (k % 2 === 0 ? 1 : -1) * 48 * DEPTH[k] + spans[k]) % spans[k];
        }
        render();
    }
    function speedBy(d) {
        stopDemo();
        mult = clamp(mult + d, 0.5, 3);
        speedEl.textContent = mult.toFixed(1);
        bump();
    }
    on(q("[data-r=slow]"), "click", function () {
        speedBy(-0.5);
    });
    on(q("[data-r=fast]"), "click", function () {
        speedBy(0.5);
    });
    on(pauseBtn, "click", function () {
        stopDemo();
        paused = !paused;
        pauseBtn.setAttribute("aria-pressed", paused ? "true" : "false");
    });
    pauseBtn.hidden = reduce;

    relayout();
    if (reduce) {
        render();
    } else {
        raf = requestAnimationFrame(frame);
    }

})();

// ColumnDriftLoop - vanilla 판(07-mr-column-drift-loop) 의 React 포트. 같은 계산을 useEffect 안에서 돌린다.
import { useEffect, useRef } from "react";
import styles from "./ColumnDriftLoop.module.scss";

type Card = {
  el: HTMLElement; ratio: number; cat: number;
  x: number; y: number; w: number; h: number; tx: number; ty: number; tw: number; th: number;
  s: number; ds: number; o: number; dop: number; vx: number; vy: number;
  ox: number; oy: number; osx: number; osy: number; ovx: number; ovy: number; ovsx: number; ovsy: number;
  fx: number; fy: number; fs: number; fo: number; t0: number; sq: number; rest: number; wait: number;
};

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

  useEffect(() => {
    const rootEl = rootRef.current;
    if (!rootEl) return;
    const root: HTMLElement = rootEl;
    const CLS = { card: styles["mr__card"], col: styles["mr__col"] };
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let demo = !reduce;
    let raf: number = 0;
    let last: number = -1;
    let ready = false;
    const offs: Array<() => void> = [];
    function q(sel: string): HTMLElement {
        return root.querySelector(sel) as HTMLElement;
    }
    const wall = q("[data-r=wall]");
    const live = q("[data-r=live]");
    function clamp(v: number, lo: number, hi: number): number {
        return Math.max(lo, Math.min(hi, v));
    }
    function makeRng(seed: number): () => number {
        let s = seed >>> 0;
        return function (): number {
            s = (Math.imul(s, 1664525) + 1013904223) >>> 0;
            return s / 4294967296;
        };
    }
    function on(el: EventTarget, type: string, fn: (e: any) => void): void {
        el.addEventListener(type, fn);
        offs.push(function (): void {
            el.removeEventListener(type, fn);
        });
    }
    function stopDemo(): void {
        if (!demo) return;
        demo = false;
        root.removeAttribute("data-demo");
        root.classList.remove("is-demo");
        live.setAttribute("aria-live", "polite");
    }
    if (reduce) live.setAttribute("aria-live", "polite");
    // 카드: 시드 LCG 로 비율을 뽑는다. 이미지 파일은 없고 그라디언트와 번호만 있다.
    function makeCards(n: number, seed: number, lo: number, hi: number): Card[] {
        const rng = makeRng(seed);
        const list: Card[] = [];
        for (let i = 0; i < n; i += 1) {
            const el = document.createElement("div");
            el.className = CLS.card;
            el.setAttribute("data-c", String(i % 6));
            el.innerHTML = "<i>" + (i + 1) + "</i>";
            wall.appendChild(el);
            list.push({
                el: el, ratio: lo + rng() * (hi - lo), cat: Math.floor(rng() * 3),
                x: 0, y: 0, w: 0, h: 0, tx: 0, ty: 0, tw: 0, th: 0,
                s: 1, ds: 1, o: 1, dop: 1, vx: 0, vy: 0,
                ox: 0, oy: 0, osx: 0, osy: 0, ovx: 0, ovy: 0, ovsx: 0, ovsy: 0,
                fx: 0, fy: 0, fs: 1, fo: 1, t0: 0, sq: 0, rest: 0, wait: 0
            });
        }
        return list;
    }
    function colW(cols: number, gap: number): number {
        return (wall.clientWidth - gap * (cols - 1)) / cols;
    }
    // 최단 열 배치: 카드를 순서대로 읽으며 지금 가장 낮은 열 끝에 얹고 그 열 높이에 카드 높이와 간격을 더한다.
    function pack(hs: number[], cols: number, cw: number, gap: number): Array<{ x: number; y: number }> {
        const colH: number[] = [];
        for (let k = 0; k < cols; k += 1) colH.push(0);
        const out: Array<{ x: number; y: number }> = [];
        for (let i = 0; i < hs.length; i += 1) {
            let best = 0;
            for (let k = 1; k < cols; k += 1) {
                if (colH[k] < colH[best] - 0.5) best = k;
            }
            out.push({ x: best * (cw + gap), y: colH[best] });
            colH[best] += hs[i] + gap;
        }
        return out;
    }
    function put(c: Card, x: number, y: number, sx: number, sy: number): void {
        const st = c.el.style;
        st.width = c.w.toFixed(1) + "px";
        st.height = c.h.toFixed(1) + "px";
        st.transform = "translate3d(" + x.toFixed(2) + "px," + y.toFixed(2) + "px,0) scale(" + sx.toFixed(3) + "," + sy.toFixed(3) + ")";
    }
    function frame(ts: number): void {
        const dt = last < 0 ? 0.016 : Math.min(0.05, (ts - last) / 1000);
        last = ts;
        if (demo) script(ts);
        step(dt, ts);
        render();
        raf = requestAnimationFrame(frame);
    }
    const ro = new ResizeObserver(function (): void {
        relayout();
    });
    ro.observe(root);

    // 기법: 열마다 속도에 깊이 비율을 곱하고 방향을 번갈아 정한다. 열 내용을 두 번 이상 이어 붙이고 위치를 한 열 높이로 나눈 나머지로 되감아 이음새를 숨긴다.
    const COLUMNS = 4;
    const GAP = 8;
    const SPEED = 64;
    const DEPTH = [1, 0.62, 1.3, 0.8];
    const PER = 5;
    const SEED = 3;
    const rng = makeRng(SEED);
    const ratios: number[] = [];
    const pos: number[] = [0, 0, 0, 0];
    const spans: number[] = [1, 1, 1, 1];
    const cols: HTMLElement[] = [];
    const speedEl = q("[data-r=speed]");
    const pauseBtn = q("[data-r=pause]");
    let mult = 1;
    let paused = false;
    for (let i = 0; i < COLUMNS * PER; i += 1) ratios.push(0.4 + rng() * 0.6);
    function build(): void {
        while (wall.firstChild) wall.removeChild(wall.firstChild);
        cols.length = 0;
        const cw = colW(COLUMNS, GAP);
        for (let k = 0; k < COLUMNS; k += 1) {
            const col = document.createElement("div");
            col.className = CLS.col;
            col.style.left = (k * (cw + GAP)).toFixed(1) + "px";
            col.style.width = cw.toFixed(1) + "px";
            let total = 0;
            for (let i = 0; i < PER; i += 1) total += ratios[k * PER + i] * cw + GAP;
            const copies = Math.ceil((total + wall.clientHeight) / total);
            for (let n = 0; n < copies; n += 1) {
                let y = n * total;
                for (let i = 0; i < PER; i += 1) {
                    const h = ratios[k * PER + i] * cw;
                    const el = document.createElement("div");
                    el.className = CLS.card;
                    el.setAttribute("data-c", String((k * PER + i) % 6));
                    el.innerHTML = "<i>" + (k * PER + i + 1) + "</i>";
                    if (n > 0) el.setAttribute("aria-hidden", "true");
                    el.style.width = cw.toFixed(1) + "px";
                    el.style.height = h.toFixed(1) + "px";
                    el.style.transform = "translate3d(0," + y.toFixed(1) + "px,0)";
                    col.appendChild(el);
                    y += h + GAP;
                }
            }
            spans[k] = total;
            cols.push(col);
            wall.appendChild(col);
        }
    }
    function relayout(): void {
        build();
        for (let k = 0; k < COLUMNS; k += 1) pos[k] = pos[k] % spans[k];
        ready = true;
        speedEl.textContent = mult.toFixed(1);
        render();
    }
    function script(ts: number): void {
        // 시연은 기본 속도로 계속 흐른다.
    }
    function step(dt: number, ts: number): void {
        if (paused) return;
        for (let k = 0; k < COLUMNS; k += 1) {
            const dir = k % 2 === 0 ? 1 : -1;
            const next = pos[k] + dir * SPEED * DEPTH[k] * mult * dt;
            pos[k] = ((next % spans[k]) + spans[k]) % spans[k];
        }
    }
    function render(): void {
        for (let k = 0; k < cols.length; k += 1) {
            cols[k].style.transform = "translate3d(0," + (-pos[k]).toFixed(1) + "px,0)";
        }
    }
    function bump(): void {
        // 움직임 줄이기에서는 흐르지 않으므로 누를 때마다 한 칸 밀어서 바뀐 결과를 바로 보여 준다.
        if (!reduce) return;
        for (let k = 0; k < COLUMNS; k += 1) {
            pos[k] = (pos[k] + (k % 2 === 0 ? 1 : -1) * 48 * DEPTH[k] + spans[k]) % spans[k];
        }
        render();
    }
    function speedBy(d: number): void {
        stopDemo();
        mult = clamp(mult + d, 0.5, 3);
        speedEl.textContent = mult.toFixed(1);
        bump();
    }
    on(q("[data-r=slow]"), "click", function (): void {
        speedBy(-0.5);
    });
    on(q("[data-r=fast]"), "click", function (): void {
        speedBy(0.5);
    });
    on(pauseBtn, "click", function (): void {
        stopDemo();
        paused = !paused;
        pauseBtn.setAttribute("aria-pressed", paused ? "true" : "false");
    });
    pauseBtn.hidden = reduce;

    relayout();
    if (reduce) {
        render();
    } else {
        raf = requestAnimationFrame(frame);
    }

    return () => {
      cancelAnimationFrame(raf);
      offs.forEach((f) => f());
      ro.disconnect();
    };
  }, []);

  return (
    <main className={styles["stage"]}>
    <div ref={rootRef} className={styles["mr"] + " is-demo"} data-demo="1">
      <div className={styles["mr__bar"]}>
        <div className={styles["mr__btns"]}><button className={styles["mr__btn"]} type="button" data-r="slow" aria-label="느리게">−</button><button className={styles["mr__btn"]} type="button" data-r="fast" aria-label="빠르게">+</button><button className={styles["mr__btn"]} type="button" data-r="pause" aria-pressed="false">멈춤</button></div>
        <p className={styles["mr__live"]} data-r="live" aria-live="off" aria-atomic="true"><span className={styles["mr__k"]}>속도</span> <b data-r="speed">1.0</b>×</p>
      </div>
      <div className={styles["mr__wall"]} data-r="wall"></div>
    </div>
    </main>
  );
}