07네 가지 색으로 하늘 그라디언트를 양자화하는 팔레트 디더 노을

<main class="stage">
<div class="sc is-demo" id="scRoot">
  <canvas class="sc__canvas" id="scCanvas" width="480" height="300" tabindex="0" aria-label="네 가지 색으로 하늘 그라디언트를 양자화하는 팔레트 디더 노을"></canvas>
  <p class="sc__status" id="scStatus" aria-live="polite">네 가지 색만으로 노을을 찍는다</p>
  <button class="sc__btn" id="scBtn" type="button">멈춤</button>
  <p class="sc__caption">네 가지 색으로 하늘 그라디언트를 양자화하는 팔레트 디더 노을</p>
</div>
</main>

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

.sc {
  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;
}

.sc__canvas {
  display: block;
  width: 100%;
  height: 100%;
  touch-action: none;
  image-rendering: pixelated;
}

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

.sc__status {
  position: absolute;
  left: $sp-3;
  top: $sp-3;
  max-width: 62%;
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(255, 255, 255, .85);
  color: $subject-ink;
  font-weight: 500;
  font-size: 11px;
  line-height: 1.4;
  pointer-events: none;
}

.sc__btn {
  position: absolute;
  right: $sp-3;
  bottom: $sp-3;
  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;
}

.sc__btn:focus-visible {
  outline: 2px solid #ffffff;
  outline-offset: 2px;
}

.sc__caption {
  position: absolute;
  left: $sp-3;
  bottom: $sp-3;
  max-width: 68%;
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(255, 255, 255, .85);
  color: $subject-ink;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

@media (max-width: 340px) {
  .sc__caption, .sc__btn { font-size: 10px; padding: $sp-1 $sp-2; }
  .sc__status { font-size: 10px; }
}

@media (prefers-reduced-motion: reduce) {
  .sc { 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);
}

.sc {
  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;
}

.sc__canvas {
  display: block;
  width: 100%;
  height: 100%;
  touch-action: none;
  image-rendering: pixelated;
}

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

.sc__status {
  position: absolute;
  left: 12px;
  top: 12px;
  max-width: 62%;
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.85);
  color: #17141a;
  font-weight: 500;
  font-size: 11px;
  line-height: 1.4;
  pointer-events: none;
}

.sc__btn {
  position: absolute;
  right: 12px;
  bottom: 12px;
  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;
}

.sc__btn:focus-visible {
  outline: 2px solid #ffffff;
  outline-offset: 2px;
}

.sc__caption {
  position: absolute;
  left: 12px;
  bottom: 12px;
  max-width: 68%;
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.85);
  color: #17141a;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

@media (max-width: 340px) {
  .sc__caption, .sc__btn {
    font-size: 10px;
    padding: 4px 8px;
  }
  .sc__status {
    font-size: 10px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .sc {
    cursor: default;
  }
}

(function () {
    const W = 480;
    const H = 300;
    const PI2 = Math.PI * 2;
    const FIXED_DT = 16;
    const REDUCE_STEP_MS = 900;
    const KEY_STEP = 14;
    const IDLE_TICKS = 150;
    const BTN_PAUSE = '멈춤';
    const BTN_PLAY = '재생';
    const BTN_NEXT = '다음 장면';
    // 점을 찍는 작은 격자 — 화면에는 3배로 확대해 올린다
    const GW = 160;
    const GH = 100;
    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 frac(x) { return x - Math.floor(x); }
    // 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;
        };
    }
    // 좌표 두 개와 시드로 0 이상 1 미만의 값을 만드는 정수 해시 (난수 함수 없이도 같은 좌표는 늘 같은 값)
    function hash2(x, y, seed) {
        let h = (Math.imul(x | 0, 374761393) + Math.imul(y | 0, 668265263) + Math.imul(seed | 0, 1442695041)) | 0;
        h = Math.imul(h ^ (h >>> 13), 1274126177);
        h ^= h >>> 16;
        return (h >>> 0) / 4294967296;
    }
    // 격자 네 점의 해시를 smooth 로 이어 붙인 값 노이즈
    function vnoise(x, y, seed) {
        const xi = Math.floor(x);
        const yi = Math.floor(y);
        const fx = smooth(x - xi);
        const fy = smooth(y - yi);
        const a = lerp(hash2(xi, yi, seed), hash2(xi + 1, yi, seed), fx);
        const b = lerp(hash2(xi, yi + 1, seed), hash2(xi + 1, yi + 1, seed), fx);
        return lerp(a, b, fy);
    }
    // 베이어 임계 행렬 — n 은 2 의 거듭제곱. 값은 0 초과 1 미만으로 맞춘다
    function makeBayer(n) {
        let size = 2;
        let m = [0, 2, 3, 1];
        const quad = [0, 2, 3, 1];
        while (size < n) {
            const s2 = size * 2;
            const next = [];
            for (let y = 0; y < s2; y += 1) {
                for (let x = 0; x < s2; x += 1) {
                    const q = (y >= size ? 2 : 0) + (x >= size ? 1 : 0);
                    next.push(4 * m[(y % size) * size + (x % size)] + quad[q]);
                }
            }
            m = next;
            size = s2;
        }
        const out = new Float32Array(n * n);
        for (let i = 0; i < out.length; i += 1) {
            out[i] = (m[i] + 0.5) / (n * n);
        }
        return out;
    }
    // 색 하나를 캔버스 픽셀 한 개(리틀 엔디언 RGBA)로 묶는다
    function pack(c) {
        return ((255 << 24) | (Math.round(c[2]) << 16) | (Math.round(c[1]) << 8) | Math.round(c[0])) >>> 0;
    }
    function mixPack(a, b, k) {
        return pack([lerp(a[0], b[0], k), lerp(a[1], b[1], k), lerp(a[2], b[2], k)]);
    }
    function makeBuf() {
        const off = document.createElement('canvas');
        off.width = GW;
        off.height = GH;
        const octx = off.getContext('2d');
        if (!octx) {
            throw new Error('2d context unavailable');
        }
        const img = octx.createImageData(GW, GH);
        return { off: off, octx: octx, img: img, px: new Uint32Array(img.data.buffer) };
    }
    // 작은 격자를 큰 캔버스에 보간 없이 확대해 올린다
    function flush(ctx, b) {
        b.octx.putImageData(b.img, 0, 0);
        ctx.imageSmoothingEnabled = false;
        ctx.drawImage(b.off, 0, 0, W, H);
    }
    function start(root, canvas, statusEl, btnEl, make) {
        const ctx0 = canvas.getContext('2d');
        if (!ctx0) {
            return function () { return; };
        }
        const ctx = ctx0;
        const dpr = Math.min(window.devicePixelRatio || 1, 2);
        canvas.width = Math.round(W * dpr);
        canvas.height = Math.round(H * dpr);
        ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
        const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
        const inp = { x: W / 2, y: H / 2, idle: 99999 };
        const scene = make(inp, reduce);
        let paused = false;
        let rafId = 0;
        let lastTs = -1;
        let accMs = 0;
        let lastLabel = '';
        const cleaners = [];
        function listen(target, type, fn) {
            target.addEventListener(type, fn);
            cleaners.push(function () { target.removeEventListener(type, fn); });
        }
        function show() {
            scene.draw(ctx);
            const t = scene.label();
            if (t !== lastLabel) {
                lastLabel = t;
                statusEl.textContent = t;
            }
        }
        function advance(ms) {
            const n = Math.round(ms / FIXED_DT);
            for (let i = 0; i < n; i += 1) {
                inp.idle += 1;
                scene.step();
            }
        }
        function refresh() {
            if (reduce) {
                advance(FIXED_DT * 6);
                show();
            }
        }
        function toLocal(e) {
            const r = canvas.getBoundingClientRect();
            inp.x = clamp((e.clientX - r.left) * W / r.width, 0, W);
            inp.y = clamp((e.clientY - r.top) * H / r.height, 0, H);
            inp.idle = 0;
        }
        function tick(ts) {
            if (lastTs < 0) {
                lastTs = ts;
            }
            const frameDt = Math.min(ts - lastTs, 160);
            lastTs = ts;
            if (!paused) {
                accMs += frameDt;
                while (accMs >= FIXED_DT) {
                    inp.idle += 1;
                    scene.step();
                    accMs -= FIXED_DT;
                }
                show();
            }
            rafId = requestAnimationFrame(tick);
        }
        btnEl.textContent = reduce ? BTN_NEXT : BTN_PAUSE;
        if (reduce) {
            root.classList.remove('is-demo');
            advance(1400);
            show();
        }
        listen(btnEl, 'click', function () {
            if (reduce) {
                advance(REDUCE_STEP_MS);
                show();
                return;
            }
            paused = !paused;
            if (paused) {
                root.classList.remove('is-demo');
            }
            else {
                root.classList.add('is-demo');
            }
            btnEl.textContent = paused ? BTN_PLAY : BTN_PAUSE;
        });
        listen(canvas, 'pointermove', function (e) {
            toLocal(e);
            refresh();
        });
        listen(canvas, 'pointerdown', function (e) {
            toLocal(e);
            scene.tap();
            refresh();
        });
        listen(canvas, 'keydown', function (e) {
            const k = e.key;
            let dx = 0;
            let dy = 0;
            if (k === 'Enter' || k === ' ') {
                e.preventDefault();
                scene.tap();
                refresh();
                return;
            }
            if (k === 'ArrowLeft') {
                dx = -KEY_STEP;
            }
            else if (k === 'ArrowRight') {
                dx = KEY_STEP;
            }
            else if (k === 'ArrowUp') {
                dy = -KEY_STEP;
            }
            else if (k === 'ArrowDown') {
                dy = KEY_STEP;
            }
            else {
                return;
            }
            e.preventDefault();
            inp.x = clamp(inp.x + dx, 0, W);
            inp.y = clamp(inp.y + dy, 0, H);
            inp.idle = 0;
            refresh();
        });
        if (!reduce) {
            rafId = requestAnimationFrame(tick);
        }
        return function () {
            cancelAnimationFrame(rafId);
            for (let i = 0; i < cleaners.length; i += 1) {
                cleaners[i]();
            }
        };
    }
    const DITHER_AMP = 0.4;
    const PALETTE_SIZE = 4;
    const HORIZON_Y = 62;
    const SUN_SPEED = 0.05;
    const SUN_R = 9;
    const PALETTE_07 = [[52, 40, 84], [142, 92, 160], [240, 132, 124], [255, 222, 170]];
    const SKY_TOP = [32, 26, 70];
    const SKY_LOW = [250, 170, 140];
    const TXT_SUNSET = '네 가지 색만으로 노을을 찍는다';
    const TXT_BAND = '진폭을 0 으로 두면 경계에 띠가 생긴다';
    const TXT_SUN = '포인터가 해의 가로 위치를 정한다';
    function makeScene(inp, reduce) {
        const buf = makeBuf();
        const matrix = makeBayer(8);
        const pal = PALETTE_07.slice(0, PALETTE_SIZE);
        const palPack = pal.map(pack);
        let t = 0;
        let banded = false;
        let sunX = GW * 0.5;
        // 보정한 색에서 가장 가까운 팔레트 색의 번호
        function nearest(r, g, b) {
            let best = 0;
            let bestD = 1e9;
            for (let k = 0; k < pal.length; k += 1) {
                const dr = r - pal[k][0];
                const dg = g - pal[k][1];
                const db = b - pal[k][2];
                const d = dr * dr + dg * dg + db * db;
                if (d < bestD) {
                    bestD = d;
                    best = k;
                }
            }
            return best;
        }
        const scene = {
            step() {
                t += 1;
                const target = inp.idle < IDLE_TICKS ? inp.x * GW / W : GW * (0.5 + 0.16 * Math.sin(t * 0.017));
                sunX = lerp(sunX, target, 0.1);
            },
            draw(ctx) {
                // 해는 수평선 위에서 오래 머물다 잠깐 아래로 잠긴다
                const h = 0.25 + 0.75 * Math.sin(t * SUN_SPEED);
                const sunY = HORIZON_Y - 8 - 34 * h;
                const day = 0.62 + 0.38 * smooth((h + 0.5) / 1.1);
                const amp = (banded ? 0 : DITHER_AMP) * 255;
                for (let y = 0; y < GH; y += 1) {
                    for (let x = 0; x < GW; x += 1) {
                        let r = 0;
                        let g = 0;
                        let b = 0;
                        if (y < HORIZON_Y) {
                            const s = Math.pow(y / HORIZON_Y, 1.3);
                            r = lerp(SKY_TOP[0], SKY_LOW[0], s);
                            g = lerp(SKY_TOP[1], SKY_LOW[1], s);
                            b = lerp(SKY_TOP[2], SKY_LOW[2], s);
                            const d = Math.hypot(x - sunX, y - sunY);
                            const glow = 0.8 * Math.exp(-(d * d) / (2 * 22 * 22)) * (0.4 + 0.6 * day);
                            r += 255 * glow * 0.8;
                            g += 200 * glow * 0.7;
                            b += 150 * glow * 0.5;
                            if (d < SUN_R && sunY < HORIZON_Y) {
                                r = 255;
                                g = 236;
                                b = 190;
                            }
                            r *= day;
                            g *= day;
                            b *= day;
                        }
                        else {
                            const depth = y - HORIZON_Y;
                            const base = 1 - 0.45 * Math.min(1, depth / 38);
                            r = SKY_LOW[0] * 0.55 * base;
                            g = SKY_LOW[1] * 0.42 * base;
                            b = SKY_LOW[2] * 0.6 * base + 26;
                            // 물결에 일렁이는 해의 반사 기둥
                            const wob = 0.5 + 0.5 * Math.sin(y * 1.2 - t * 0.2 + Math.sin(x * 0.15) * 2);
                            const width = 6 + depth * 0.25;
                            const refl = Math.exp(-((x - sunX) * (x - sunX)) / (2 * width * width)) * 0.7 * wob * (sunY < HORIZON_Y + 12 ? 1 : 0.4);
                            r += 255 * refl * day;
                            g += 205 * refl * day;
                            b += 160 * refl * day;
                        }
                        const off = (matrix[(y & 7) * 8 + (x & 7)] - 0.5) * amp;
                        buf.px[y * GW + x] = palPack[nearest(r + off, g + off, b + off)];
                    }
                }
                flush(ctx, buf);
            },
            label() {
                if (banded) {
                    return TXT_BAND;
                }
                return inp.idle < IDLE_TICKS ? TXT_SUN : TXT_SUNSET;
            },
            tap() {
                banded = !banded;
            }
        };
        if (reduce) {
            for (let i = 0; i < 24; i += 1) {
                scene.step();
            }
        }
        return scene;
    }
    start(document.getElementById('scRoot'), document.getElementById('scCanvas'), document.getElementById('scStatus'), document.getElementById('scBtn'), makeScene);
})();

import { useEffect, useRef } from "react";
import styles from "./DtPaletteSunsetQuantize.module.scss";

const W = 480;
const H = 300;
const PI2 = Math.PI * 2;
const FIXED_DT = 16;
const REDUCE_STEP_MS = 900;
const KEY_STEP = 14;
const IDLE_TICKS = 150;
const BTN_PAUSE = '멈춤';
const BTN_PLAY = '재생';
const BTN_NEXT = '다음 장면';
// 점을 찍는 작은 격자 — 화면에는 3배로 확대해 올린다
const GW = 160;
const GH = 100;

type RGB = [number, number, number];
interface Input { x: number; y: number; idle: number; }
interface Scene {
    step(): void;
    draw(ctx: CanvasRenderingContext2D): void;
    label(): string;
    tap(): void;
}
type Maker = (inp: Input, reduce: boolean) => Scene;
interface Buf {
    off: HTMLCanvasElement;
    octx: CanvasRenderingContext2D;
    img: ImageData;
    px: Uint32Array;
}

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 frac(x: number): number { return x - Math.floor(x); }
// 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;
    };
}
// 좌표 두 개와 시드로 0 이상 1 미만의 값을 만드는 정수 해시 (난수 함수 없이도 같은 좌표는 늘 같은 값)
function hash2(x: number, y: number, seed: number): number {
    let h = (Math.imul(x | 0, 374761393) + Math.imul(y | 0, 668265263) + Math.imul(seed | 0, 1442695041)) | 0;
    h = Math.imul(h ^ (h >>> 13), 1274126177);
    h ^= h >>> 16;
    return (h >>> 0) / 4294967296;
}
// 격자 네 점의 해시를 smooth 로 이어 붙인 값 노이즈
function vnoise(x: number, y: number, seed: number): number {
    const xi = Math.floor(x);
    const yi = Math.floor(y);
    const fx = smooth(x - xi);
    const fy = smooth(y - yi);
    const a = lerp(hash2(xi, yi, seed), hash2(xi + 1, yi, seed), fx);
    const b = lerp(hash2(xi, yi + 1, seed), hash2(xi + 1, yi + 1, seed), fx);
    return lerp(a, b, fy);
}
// 베이어 임계 행렬 — n 은 2 의 거듭제곱. 값은 0 초과 1 미만으로 맞춘다
function makeBayer(n: number): Float32Array {
    let size = 2;
    let m: number[] = [0, 2, 3, 1];
    const quad = [0, 2, 3, 1];
    while (size < n) {
        const s2 = size * 2;
        const next: number[] = [];
        for (let y = 0; y < s2; y += 1) {
            for (let x = 0; x < s2; x += 1) {
                const q = (y >= size ? 2 : 0) + (x >= size ? 1 : 0);
                next.push(4 * m[(y % size) * size + (x % size)] + quad[q]);
            }
        }
        m = next;
        size = s2;
    }
    const out = new Float32Array(n * n);
    for (let i = 0; i < out.length; i += 1) {
        out[i] = (m[i] + 0.5) / (n * n);
    }
    return out;
}
// 색 하나를 캔버스 픽셀 한 개(리틀 엔디언 RGBA)로 묶는다
function pack(c: RGB): number {
    return ((255 << 24) | (Math.round(c[2]) << 16) | (Math.round(c[1]) << 8) | Math.round(c[0])) >>> 0;
}
function mixPack(a: RGB, b: RGB, k: number): number {
    return pack([lerp(a[0], b[0], k), lerp(a[1], b[1], k), lerp(a[2], b[2], k)]);
}
function makeBuf(): Buf {
    const off = document.createElement('canvas');
    off.width = GW;
    off.height = GH;
    const octx = off.getContext('2d');
    if (!octx) {
        throw new Error('2d context unavailable');
    }
    const img = octx.createImageData(GW, GH);
    return { off: off, octx: octx, img: img, px: new Uint32Array(img.data.buffer) };
}
// 작은 격자를 큰 캔버스에 보간 없이 확대해 올린다
function flush(ctx: CanvasRenderingContext2D, b: Buf): void {
    b.octx.putImageData(b.img, 0, 0);
    ctx.imageSmoothingEnabled = false;
    ctx.drawImage(b.off, 0, 0, W, H);
}


function start(root: HTMLElement, canvas: HTMLCanvasElement, statusEl: HTMLElement, btnEl: HTMLButtonElement, make: Maker): () => void {
    const ctx0 = canvas.getContext('2d');
    if (!ctx0) {
        return function (): void { return; };
    }
    const ctx: CanvasRenderingContext2D = ctx0;
    const dpr = Math.min(window.devicePixelRatio || 1, 2);
    canvas.width = Math.round(W * dpr);
    canvas.height = Math.round(H * dpr);
    ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
    const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
    const inp: Input = { x: W / 2, y: H / 2, idle: 99999 };
    const scene = make(inp, reduce);
    let paused = false;
    let rafId = 0;
    let lastTs = -1;
    let accMs = 0;
    let lastLabel = '';
    const cleaners: Array<() => void> = [];
    function listen(target: EventTarget, type: string, fn: (e: Event) => void): void {
        target.addEventListener(type, fn);
        cleaners.push(function (): void { target.removeEventListener(type, fn); });
    }
    function show(): void {
        scene.draw(ctx);
        const t = scene.label();
        if (t !== lastLabel) {
            lastLabel = t;
            statusEl.textContent = t;
        }
    }
    function advance(ms: number): void {
        const n = Math.round(ms / FIXED_DT);
        for (let i = 0; i < n; i += 1) {
            inp.idle += 1;
            scene.step();
        }
    }
    function refresh(): void {
        if (reduce) {
            advance(FIXED_DT * 6);
            show();
        }
    }
    function toLocal(e: PointerEvent): void {
        const r = canvas.getBoundingClientRect();
        inp.x = clamp((e.clientX - r.left) * W / r.width, 0, W);
        inp.y = clamp((e.clientY - r.top) * H / r.height, 0, H);
        inp.idle = 0;
    }
    function tick(ts: number): void {
        if (lastTs < 0) {
            lastTs = ts;
        }
        const frameDt = Math.min(ts - lastTs, 160);
        lastTs = ts;
        if (!paused) {
            accMs += frameDt;
            while (accMs >= FIXED_DT) {
                inp.idle += 1;
                scene.step();
                accMs -= FIXED_DT;
            }
            show();
        }
        rafId = requestAnimationFrame(tick);
    }
    btnEl.textContent = reduce ? BTN_NEXT : BTN_PAUSE;
    if (reduce) {
        root.classList.remove('is-demo');
        advance(1400);
        show();
    }
    listen(btnEl, 'click', function (): void {
        if (reduce) {
            advance(REDUCE_STEP_MS);
            show();
            return;
        }
        paused = !paused;
        if (paused) {
            root.classList.remove('is-demo');
        } else {
            root.classList.add('is-demo');
        }
        btnEl.textContent = paused ? BTN_PLAY : BTN_PAUSE;
    });
    listen(canvas, 'pointermove', function (e: Event): void {
        toLocal(e as PointerEvent);
        refresh();
    });
    listen(canvas, 'pointerdown', function (e: Event): void {
        toLocal(e as PointerEvent);
        scene.tap();
        refresh();
    });
    listen(canvas, 'keydown', function (e: Event): void {
        const k = (e as KeyboardEvent).key;
        let dx = 0;
        let dy = 0;
        if (k === 'Enter' || k === ' ') {
            e.preventDefault();
            scene.tap();
            refresh();
            return;
        }
        if (k === 'ArrowLeft') { dx = -KEY_STEP; }
        else if (k === 'ArrowRight') { dx = KEY_STEP; }
        else if (k === 'ArrowUp') { dy = -KEY_STEP; }
        else if (k === 'ArrowDown') { dy = KEY_STEP; }
        else { return; }
        e.preventDefault();
        inp.x = clamp(inp.x + dx, 0, W);
        inp.y = clamp(inp.y + dy, 0, H);
        inp.idle = 0;
        refresh();
    });
    if (!reduce) {
        rafId = requestAnimationFrame(tick);
    }
    return function (): void {
        cancelAnimationFrame(rafId);
        for (let i = 0; i < cleaners.length; i += 1) {
            cleaners[i]();
        }
    };
}

const DITHER_AMP = 0.4;
const PALETTE_SIZE = 4;
const HORIZON_Y = 62;
const SUN_SPEED = 0.05;
const SUN_R = 9;
const PALETTE_07: RGB[] = [[52, 40, 84], [142, 92, 160], [240, 132, 124], [255, 222, 170]];
const SKY_TOP: RGB = [32, 26, 70];
const SKY_LOW: RGB = [250, 170, 140];
const TXT_SUNSET = '네 가지 색만으로 노을을 찍는다';
const TXT_BAND = '진폭을 0 으로 두면 경계에 띠가 생긴다';
const TXT_SUN = '포인터가 해의 가로 위치를 정한다';

function makeScene(inp: Input, reduce: boolean): Scene {
    const buf = makeBuf();
    const matrix = makeBayer(8);
    const pal = PALETTE_07.slice(0, PALETTE_SIZE);
    const palPack = pal.map(pack);
    let t = 0;
    let banded = false;
    let sunX = GW * 0.5;
    // 보정한 색에서 가장 가까운 팔레트 색의 번호
    function nearest(r: number, g: number, b: number): number {
        let best = 0;
        let bestD = 1e9;
        for (let k = 0; k < pal.length; k += 1) {
            const dr = r - pal[k][0];
            const dg = g - pal[k][1];
            const db = b - pal[k][2];
            const d = dr * dr + dg * dg + db * db;
            if (d < bestD) {
                bestD = d;
                best = k;
            }
        }
        return best;
    }
    const scene: Scene = {
        step(): void {
            t += 1;
            const target = inp.idle < IDLE_TICKS ? inp.x * GW / W : GW * (0.5 + 0.16 * Math.sin(t * 0.017));
            sunX = lerp(sunX, target, 0.1);
        },
        draw(ctx: CanvasRenderingContext2D): void {
            // 해는 수평선 위에서 오래 머물다 잠깐 아래로 잠긴다
            const h = 0.25 + 0.75 * Math.sin(t * SUN_SPEED);
            const sunY = HORIZON_Y - 8 - 34 * h;
            const day = 0.62 + 0.38 * smooth((h + 0.5) / 1.1);
            const amp = (banded ? 0 : DITHER_AMP) * 255;
            for (let y = 0; y < GH; y += 1) {
                for (let x = 0; x < GW; x += 1) {
                    let r = 0;
                    let g = 0;
                    let b = 0;
                    if (y < HORIZON_Y) {
                        const s = Math.pow(y / HORIZON_Y, 1.3);
                        r = lerp(SKY_TOP[0], SKY_LOW[0], s);
                        g = lerp(SKY_TOP[1], SKY_LOW[1], s);
                        b = lerp(SKY_TOP[2], SKY_LOW[2], s);
                        const d = Math.hypot(x - sunX, y - sunY);
                        const glow = 0.8 * Math.exp(-(d * d) / (2 * 22 * 22)) * (0.4 + 0.6 * day);
                        r += 255 * glow * 0.8;
                        g += 200 * glow * 0.7;
                        b += 150 * glow * 0.5;
                        if (d < SUN_R && sunY < HORIZON_Y) {
                            r = 255;
                            g = 236;
                            b = 190;
                        }
                        r *= day;
                        g *= day;
                        b *= day;
                    } else {
                        const depth = y - HORIZON_Y;
                        const base = 1 - 0.45 * Math.min(1, depth / 38);
                        r = SKY_LOW[0] * 0.55 * base;
                        g = SKY_LOW[1] * 0.42 * base;
                        b = SKY_LOW[2] * 0.6 * base + 26;
                        // 물결에 일렁이는 해의 반사 기둥
                        const wob = 0.5 + 0.5 * Math.sin(y * 1.2 - t * 0.2 + Math.sin(x * 0.15) * 2);
                        const width = 6 + depth * 0.25;
                        const refl = Math.exp(-((x - sunX) * (x - sunX)) / (2 * width * width)) * 0.7 * wob * (sunY < HORIZON_Y + 12 ? 1 : 0.4);
                        r += 255 * refl * day;
                        g += 205 * refl * day;
                        b += 160 * refl * day;
                    }
                    const off = (matrix[(y & 7) * 8 + (x & 7)] - 0.5) * amp;
                    buf.px[y * GW + x] = palPack[nearest(r + off, g + off, b + off)];
                }
            }
            flush(ctx, buf);
        },
        label(): string {
            if (banded) {
                return TXT_BAND;
            }
            return inp.idle < IDLE_TICKS ? TXT_SUN : TXT_SUNSET;
        },
        tap(): void {
            banded = !banded;
        }
    };
    if (reduce) {
        for (let i = 0; i < 24; i += 1) {
            scene.step();
        }
    }
    return scene;
}

export default function DtPaletteSunsetQuantize() {
  const rootRef = useRef<HTMLDivElement | null>(null);
  const canvasRef = useRef<HTMLCanvasElement | null>(null);
  const statusRef = useRef<HTMLParagraphElement | null>(null);
  const btnRef = useRef<HTMLButtonElement | null>(null);

  useEffect(() => {
    const root = rootRef.current;
    const canvas = canvasRef.current;
    const statusEl = statusRef.current;
    const btnEl = btnRef.current;
    if (!root || !canvas || !statusEl || !btnEl) return;
    return start(root, canvas, statusEl, btnEl, makeScene);
  }, []);

  return (
    <main className={styles.stage}>
      <div className={`${styles.sc} is-demo`} ref={rootRef}>
        <canvas className={styles.sc__canvas} ref={canvasRef} width={480} height={300} tabIndex={0} aria-label="네 가지 색으로 하늘 그라디언트를 양자화하는 팔레트 디더 노을" />
        <p className={styles.sc__status} ref={statusRef} aria-live="polite">네 가지 색만으로 노을을 찍는다</p>
        <button className={styles.sc__btn} ref={btnRef} type="button">멈춤</button>
        <p className={styles.sc__caption}>네 가지 색으로 하늘 그라디언트를 양자화하는 팔레트 디더 노을</p>
      </div>
    </main>
  );
}