05A Total Line Where Digits Roll Vertically as Items Are Added and the Tax Row Follows One Beat Late

<main class="stage">
<div class="rc is-demo" id="rc">
  <canvas class="rc__canvas" data-role="canvas" width="480" height="300" aria-label="Each time an item is added the total wheels roll up with inertia and the tax line follows one beat later"></canvas>
  <p class="rc__status" data-role="status" aria-live="polite">Empty</p>
  <div class="rc__tools">
    <button class="rc__btn" data-role="btn" type="button">Add item</button>
    <button class="rc__btn" data-role="clear" type="button">Clear</button>
  </div>
</div>
</main>

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

.rc {
  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;
}

.rc__canvas {
  display: block;
  width: 100%;
  height: 100%;
}

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

.rc__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;
}

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

.rc__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;
}

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

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

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

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

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

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

.rc {
  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;
}

.rc__canvas {
  display: block;
  width: 100%;
  height: 100%;
}

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

.rc__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;
}

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

.rc__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;
}

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

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

@media (max-width: 340px) {
  .rc__btn {
    font-size: 10px;
    padding: 4px 8px;
  }
  .rc__status {
    font-size: 10px;
    padding: 4px 8px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .rc {
    cursor: default;
  }
  .rc__chip {
    cursor: default;
  }
}

(function () {
    const root = document.getElementById("rc");
    if (!root) return;
    const W = 480;
    const H = 300;
    const FIXED_DT = 16;
    // 파스텔 팔레트 — 어두운 무대 위에 밝은 종이를 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];
    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)]; }
    // 시드 고정 난수 — 같은 시드면 언제나 같은 수열 (선형 합동 방식)
    function lcg(seed) {
        let s = seed >>> 0;
        return function () {
            s = (Math.imul(s, 1664525) + 1013904223) >>> 0;
            return s / 4294967296;
        };
    }
    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)');
    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();
        if (reduceQuery.matches) {
            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];
    }
    const DIGIT_H = 62;
    const INERTIA = 0.9;
    const PULL_K = 0.0052;
    const TAX_RATE = 0.1;
    const DELAY_MS = 260;
    const ADD_MS = 440;
    const HOLD_MS = 900;
    const TXT_SUM = 'Total';
    const TXT_TAX = 'Tax';
    const TXT_COUNT = ' items added — total ';
    const TXT_EMPTY = 'Empty';
    const NAMES = ['Milk', 'Bread', 'Apples', 'Eggs', 'Tangerines'];
    const PRICES = [1200, 2800, 3500, 4100, 1900];
    const addBtn = root.querySelector('[data-role="btn"]');
    const clearBtn = root.querySelector('[data-role="clear"]');
    let count = 0;
    let target = 0;
    let shown = 0;
    let speed = 0;
    let taxShown = 0;
    let clock = 0;
    let nextAt = 200;
    let userTouched = false;
    const addedAt = [];
    function totalOf(n) {
        let s = 0;
        for (let i = 0; i < n; i += 1) {
            s += PRICES[i];
        }
        return s;
    }
    // 숫자 판 하나가 놓이는 위치 — 올림이 일어나는 구간(바로 아래 자리가 9.9 를 넘길 때)에만 구른다
    function digitPos(value, d) {
        if (d === 0) {
            return value;
        }
        const scale = Math.pow(10, d);
        const base = Math.floor(value / scale);
        const f = value / scale - base;
        return base + smooth((f - 0.9) / 0.1);
    }
    function announce() {
        status.textContent = count === 0 ? TXT_EMPTY : count + TXT_COUNT + target;
    }
    function addItem() {
        if (count >= PRICES.length) {
            return;
        }
        addedAt[count] = clock;
        count += 1;
        target = totalOf(count);
        announce();
    }
    function clearAll() {
        count = 0;
        target = 0;
        announce();
    }
    function step() {
        clock += FIXED_DT;
        if (!userTouched && clock >= nextAt) {
            if (count >= PRICES.length) {
                clearAll();
                nextAt = clock + 700;
            }
            else {
                addItem();
                nextAt = clock + (count >= PRICES.length ? HOLD_MS : ADD_MS);
            }
        }
        // 관성 — 목표를 지나쳤다가 되돌아와 멈춘다
        speed = speed * INERTIA + (target - shown) * PULL_K * (FIXED_DT / 16);
        shown = Math.max(0, shown + speed);
        // Tax 줄은 화면에 보이는 합계를 한 박자 늦게 따라간다 (지연 필터)
        taxShown += (shown * TAX_RATE - taxShown) * (1 - Math.exp(-FIXED_DT / DELAY_MS));
    }
    function settle() {
        count = PRICES.length;
        target = totalOf(count);
        shown = target;
        taxShown = target * TAX_RATE;
        for (let i = 0; i < count; i += 1) {
            addedAt[i] = -9999;
        }
        announce();
    }
    function drawWheel(x, y, w, h, p, dim, size) {
        ctx.fillStyle = rgba(mix(BG, LILAC, 0.22), 1);
        ctx.fillRect(x, y, w, h);
        ctx.save();
        ctx.beginPath();
        ctx.rect(x, y, w, h);
        ctx.clip();
        const base = Math.floor(p);
        const f = p - base;
        ctx.font = '700 ' + size + 'px ui-monospace, "Noto Sans KR", monospace';
        ctx.textAlign = 'center';
        ctx.textBaseline = 'middle';
        ctx.fillStyle = rgba(PAPER, dim ? 0.22 : 1);
        const a = ((base % 10) + 10) % 10;
        ctx.fillText(String(a), x + w / 2, y + h / 2 - f * h);
        ctx.fillText(String((a + 1) % 10), x + w / 2, y + h / 2 + (1 - f) * h);
        // 둥근 판의 위아래가 어두워지는 음영
        const sh = ctx.createLinearGradient(0, y, 0, y + h);
        sh.addColorStop(0, rgba(BG, 0.85));
        sh.addColorStop(0.28, rgba(BG, 0));
        sh.addColorStop(0.72, rgba(BG, 0));
        sh.addColorStop(1, rgba(BG, 0.85));
        ctx.fillStyle = sh;
        ctx.fillRect(x, y, w, h);
        ctx.restore();
        ctx.textBaseline = 'alphabetic';
    }
    function drawOdometer(x, y, digits, value, w, h, size) {
        for (let k = 0; k < digits; k += 1) {
            const d = digits - 1 - k;
            const lead = value < Math.pow(10, d) - 0.5 && d > 0;
            drawWheel(x + k * (w + 4), y, w, h, digitPos(value, d), lead, size);
        }
    }
    function draw() {
        ctx.fillStyle = rgba(BG, 1);
        ctx.fillRect(0, 0, W, H);
        // 왼쪽 영수증 종이
        ctx.fillStyle = rgba([10, 8, 22], 0.45);
        ctx.fillRect(34, 24, 196, 240);
        ctx.fillStyle = rgba(PAPER, 1);
        ctx.fillRect(28, 18, 196, 240);
        ctx.fillStyle = rgba(INK, 0.07);
        for (let y = 22; y < 256; y += 8) {
            ctx.fillRect(28, y, 196, 1);
        }
        ctx.font = '600 13px "Noto Sans KR", ui-monospace, monospace';
        for (let i = 0; i < count; i += 1) {
            const age = clamp((clock - addedAt[i]) / 240, 0, 1);
            const y = 52 + i * 34;
            ctx.fillStyle = rgba(INK, smooth(age));
            ctx.textAlign = 'left';
            ctx.fillText(NAMES[i], 44 - (1 - smooth(age)) * 26, y);
            ctx.textAlign = 'right';
            ctx.fillText(String(PRICES[i]), 208 + (1 - smooth(age)) * 26, y);
            ctx.fillStyle = rgba(INK, 0.16 * smooth(age));
            ctx.fillRect(40, y + 10, 168, 1);
        }
        // 오른쪽 숫자 판
        ctx.font = '700 14px "Noto Sans KR", ui-monospace, monospace';
        ctx.textAlign = 'left';
        ctx.fillStyle = rgba(PAPER, 0.9);
        ctx.fillText(TXT_SUM, 256, 58);
        drawOdometer(256, 70, 5, shown, 38, DIGIT_H, 46);
        ctx.fillStyle = rgba(PAPER, 0.9);
        ctx.font = '700 14px "Noto Sans KR", ui-monospace, monospace';
        ctx.fillText(TXT_TAX, 256, 172);
        drawOdometer(256, 184, 4, taxShown, 30, 44, 32);
    }
    function press() {
        userTouched = true;
        if (reduceQuery.matches) {
            addItem();
            shown = target;
            taxShown = target * TAX_RATE;
            draw();
            return;
        }
        addItem();
    }
    if (addBtn) {
        addBtn.addEventListener('click', press);
    }
    if (clearBtn) {
        clearBtn.addEventListener('click', function () {
            userTouched = true;
            clearAll();
            if (reduceQuery.matches) {
                shown = 0;
                taxShown = 0;
                draw();
            }
        });
    }
    let rafId = 0;
    let lastTs = -1;
    let acc = 0;
    function frame(ts) {
        if (lastTs < 0) {
            lastTs = ts;
        }
        acc += Math.min(ts - lastTs, 100);
        lastTs = ts;
        let n = 0;
        while (acc >= FIXED_DT && n < 6) {
            step();
            acc -= FIXED_DT;
            n += 1;
        }
        draw();
        rafId = window.requestAnimationFrame(frame);
    }
    if (reduceQuery.matches) {
        settle();
        draw();
    }
    else {
        rafId = window.requestAnimationFrame(frame);
    }
    return function () {
        window.cancelAnimationFrame(rafId);
        window.removeEventListener('resize', onResize);
    };
})();

// RecTotalOdometerRollTaxTick - vanilla 판(05-rec-total-odometer-roll-tax-tick) 의 React 포트. 같은 계산을 useEffect 안에서 돌린다.
import { useEffect, useRef } from "react";
import styles from "./RecTotalOdometerRollTaxTick.module.scss";

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

export default function RecTotalOdometerRollTaxTick() {
  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 종이를 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];
    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)]; }
    // 시드 고정 난수 — 같은 시드면 언제나 같은 수열 (선형 합동 방식)
    function lcg(seed: number): () => number {
        let s = seed >>> 0;
        return function (): number {
            s = (Math.imul(s, 1664525) + 1013904223) >>> 0;
            return s / 4294967296;
        };
    }
    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)');
    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();
        if (reduceQuery.matches) { 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];
    }
    const DIGIT_H = 62;
    const INERTIA = 0.9;
    const PULL_K = 0.0052;
    const TAX_RATE = 0.1;
    const DELAY_MS = 260;
    const ADD_MS = 440;
    const HOLD_MS = 900;
    const TXT_SUM = '합계';
    const TXT_TAX = '세금';
    const TXT_COUNT = '개 담김 — 합계 ';
    const TXT_EMPTY = '비어 있음';
    const NAMES: string[] = ['우유', '식빵', '사과', '달걀', '귤'];
    const PRICES: number[] = [1200, 2800, 3500, 4100, 1900];
    const addBtn = root.querySelector('[data-role="btn"]') as HTMLButtonElement | null;
    const clearBtn = root.querySelector('[data-role="clear"]') as HTMLButtonElement | null;
    let count = 0;
    let target = 0;
    let shown = 0;
    let speed = 0;
    let taxShown = 0;
    let clock = 0;
    let nextAt = 200;
    let userTouched = false;
    const addedAt: number[] = [];
    function totalOf(n: number): number {
        let s = 0;
        for (let i = 0; i < n; i += 1) { s += PRICES[i]; }
        return s;
    }
    // 숫자 판 하나가 놓이는 위치 — 올림이 일어나는 구간(바로 아래 자리가 9.9 를 넘길 때)에만 구른다
    function digitPos(value: number, d: number): number {
        if (d === 0) { return value; }
        const scale = Math.pow(10, d);
        const base = Math.floor(value / scale);
        const f = value / scale - base;
        return base + smooth((f - 0.9) / 0.1);
    }
    function announce(): void {
        status.textContent = count === 0 ? TXT_EMPTY : count + TXT_COUNT + target;
    }
    function addItem(): void {
        if (count >= PRICES.length) { return; }
        addedAt[count] = clock;
        count += 1;
        target = totalOf(count);
        announce();
    }
    function clearAll(): void {
        count = 0;
        target = 0;
        announce();
    }
    function step(): void {
        clock += FIXED_DT;
        if (!userTouched && clock >= nextAt) {
            if (count >= PRICES.length) {
                clearAll();
                nextAt = clock + 700;
            } else {
                addItem();
                nextAt = clock + (count >= PRICES.length ? HOLD_MS : ADD_MS);
            }
        }
        // 관성 — 목표를 지나쳤다가 되돌아와 멈춘다
        speed = speed * INERTIA + (target - shown) * PULL_K * (FIXED_DT / 16);
        shown = Math.max(0, shown + speed);
        // 세금 줄은 화면에 보이는 합계를 한 박자 늦게 따라간다 (지연 필터)
        taxShown += (shown * TAX_RATE - taxShown) * (1 - Math.exp(-FIXED_DT / DELAY_MS));
    }
    function settle(): void {
        count = PRICES.length;
        target = totalOf(count);
        shown = target;
        taxShown = target * TAX_RATE;
        for (let i = 0; i < count; i += 1) { addedAt[i] = -9999; }
        announce();
    }
    function drawWheel(x: number, y: number, w: number, h: number, p: number, dim: boolean, size: number): void {
        ctx.fillStyle = rgba(mix(BG, LILAC, 0.22), 1);
        ctx.fillRect(x, y, w, h);
        ctx.save();
        ctx.beginPath();
        ctx.rect(x, y, w, h);
        ctx.clip();
        const base = Math.floor(p);
        const f = p - base;
        ctx.font = '700 ' + size + 'px ui-monospace, "Noto Sans KR", monospace';
        ctx.textAlign = 'center';
        ctx.textBaseline = 'middle';
        ctx.fillStyle = rgba(PAPER, dim ? 0.22 : 1);
        const a = ((base % 10) + 10) % 10;
        ctx.fillText(String(a), x + w / 2, y + h / 2 - f * h);
        ctx.fillText(String((a + 1) % 10), x + w / 2, y + h / 2 + (1 - f) * h);
        // 둥근 판의 위아래가 어두워지는 음영
        const sh = ctx.createLinearGradient(0, y, 0, y + h);
        sh.addColorStop(0, rgba(BG, 0.85));
        sh.addColorStop(0.28, rgba(BG, 0));
        sh.addColorStop(0.72, rgba(BG, 0));
        sh.addColorStop(1, rgba(BG, 0.85));
        ctx.fillStyle = sh;
        ctx.fillRect(x, y, w, h);
        ctx.restore();
        ctx.textBaseline = 'alphabetic';
    }
    function drawOdometer(x: number, y: number, digits: number, value: number, w: number, h: number, size: number): void {
        for (let k = 0; k < digits; k += 1) {
            const d = digits - 1 - k;
            const lead = value < Math.pow(10, d) - 0.5 && d > 0;
            drawWheel(x + k * (w + 4), y, w, h, digitPos(value, d), lead, size);
        }
    }
    function draw(): void {
        ctx.fillStyle = rgba(BG, 1);
        ctx.fillRect(0, 0, W, H);
        // 왼쪽 영수증 종이
        ctx.fillStyle = rgba([10, 8, 22], 0.45);
        ctx.fillRect(34, 24, 196, 240);
        ctx.fillStyle = rgba(PAPER, 1);
        ctx.fillRect(28, 18, 196, 240);
        ctx.fillStyle = rgba(INK, 0.07);
        for (let y = 22; y < 256; y += 8) { ctx.fillRect(28, y, 196, 1); }
        ctx.font = '600 13px "Noto Sans KR", ui-monospace, monospace';
        for (let i = 0; i < count; i += 1) {
            const age = clamp((clock - addedAt[i]) / 240, 0, 1);
            const y = 52 + i * 34;
            ctx.fillStyle = rgba(INK, smooth(age));
            ctx.textAlign = 'left';
            ctx.fillText(NAMES[i], 44 - (1 - smooth(age)) * 26, y);
            ctx.textAlign = 'right';
            ctx.fillText(String(PRICES[i]), 208 + (1 - smooth(age)) * 26, y);
            ctx.fillStyle = rgba(INK, 0.16 * smooth(age));
            ctx.fillRect(40, y + 10, 168, 1);
        }
        // 오른쪽 숫자 판
        ctx.font = '700 14px "Noto Sans KR", ui-monospace, monospace';
        ctx.textAlign = 'left';
        ctx.fillStyle = rgba(PAPER, 0.9);
        ctx.fillText(TXT_SUM, 256, 58);
        drawOdometer(256, 70, 5, shown, 38, DIGIT_H, 46);
        ctx.fillStyle = rgba(PAPER, 0.9);
        ctx.font = '700 14px "Noto Sans KR", ui-monospace, monospace';
        ctx.fillText(TXT_TAX, 256, 172);
        drawOdometer(256, 184, 4, taxShown, 30, 44, 32);
    }
    function press(): void {
        userTouched = true;
        if (reduceQuery.matches) {
            addItem();
            shown = target;
            taxShown = target * TAX_RATE;
            draw();
            return;
        }
        addItem();
    }
    if (addBtn) { addBtn.addEventListener('click', press); }
    if (clearBtn) {
        clearBtn.addEventListener('click', function (): void {
            userTouched = true;
            clearAll();
            if (reduceQuery.matches) { shown = 0; taxShown = 0; draw(); }
        });
    }

    let rafId = 0;
    let lastTs = -1;
    let acc = 0;
    function frame(ts: number): void {
        if (lastTs < 0) { lastTs = ts; }
        acc += Math.min(ts - lastTs, 100);
        lastTs = ts;
        let n = 0;
        while (acc >= FIXED_DT && n < 6) {
            step();
            acc -= FIXED_DT;
            n += 1;
        }
        draw();
        rafId = window.requestAnimationFrame(frame);
    }
    if (reduceQuery.matches) {
        settle();
        draw();
    } else {
        rafId = window.requestAnimationFrame(frame);
    }
    return function (): void {
        window.cancelAnimationFrame(rafId);
        window.removeEventListener('resize', onResize);
    };

  }, []);

  return (
    <div className={cx("rc") + " is-demo"} ref={rootRef}>
        <canvas className={cx("rc__canvas")} data-role="canvas" width={480} height={300} aria-label="품목이 담길 때마다 합계 숫자판이 관성으로 굴러 올라가고 세금 줄이 한 박자 늦게 따라가는 장면"></canvas>
        <p className={cx("rc__status")} data-role="status" aria-live="polite">비어 있음</p>
        <div className={cx("rc__tools")}>
          <button className={cx("rc__btn")} data-role="btn" type="button">품목 추가</button>
          <button className={cx("rc__btn")} data-role="clear" type="button">비우기</button>
        </div>
    </div>
  );
}