03A Night Sky Where a Noise Field Twinkles Each Star Differently

<main class="stage">
<div class="sc is-demo" id="scRoot">
  <canvas class="sc__canvas" id="scCanvas" width="480" height="300" tabindex="0" aria-label="A Night Sky Where a Noise Field Twinkles Each Star Differently"></canvas>
  <p class="sc__status" id="scStatus" aria-live="polite">Noise field — neighboring stars shimmer together</p>
  <button class="sc__btn" id="scBtn" type="button">Pause</button>
  <p class="sc__caption">A Night Sky Where a Noise Field Twinkles Each Star Differently</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;
}

.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;
}

.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 = 'Pause';
    const BTN_PLAY = 'Play';
    const BTN_NEXT = 'Next scene';
    const BG = [14, 12, 32];
    const STAR_RGBS = [[226, 238, 255], [255, 222, 196], [208, 196, 255], [196, 240, 228], [255, 206, 226]];
    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;
        };
    }
    function glow(ctx, x, y, r, c, a) {
        const g = ctx.createRadialGradient(x, y, 0, x, y, r);
        g.addColorStop(0, rgba(c, a));
        g.addColorStop(1, rgba(c, 0));
        ctx.fillStyle = g;
        ctx.fillRect(x - r, y - r, r * 2, r * 2);
    }
    function paintBg(ctx, alpha) {
        ctx.fillStyle = rgba(BG, alpha);
        ctx.fillRect(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 NOISE_SCALE = 0.011;
    const TWINKLE_SPEED = 0.035;
    const CONTRAST = 2.6;
    const SEED = 7;
    const STAR_TOTAL = 360;
    const NEBULA_W = 60;
    const NEBULA_H = 38;
    const TXT_FIELD = 'Noise field — neighboring stars shimmer together';
    const TXT_RESEED = 'New seed — same formula, different sky';
    // 격자 점의 값 — 정수 두 개와 시드를 섞어 0 이상 1 미만으로
    function hash2(ix, iy, seed) {
        let h = Math.imul(ix | 0, 374761393) + Math.imul(iy | 0, 668265263) + Math.imul(seed | 0, 1442695041);
        h = Math.imul(h ^ (h >>> 13), 1274126177);
        return ((h ^ (h >>> 16)) >>> 0) / 4294967296;
    }
    // 2차원 값 노이즈 — 네 격자 점을 부드럽게 보간
    function vnoise(x, y, seed) {
        const ix = Math.floor(x);
        const iy = Math.floor(y);
        const fx = smooth(x - ix);
        const fy = smooth(y - iy);
        return lerp(lerp(hash2(ix, iy, seed), hash2(ix + 1, iy, seed), fx), lerp(hash2(ix, iy + 1, seed), hash2(ix + 1, iy + 1, seed), fx), fy);
    }
    function makeScene(inp, reduce) {
        const rnd = lcg(450303);
        const sparks = [];
        for (let i = 0; i < STAR_TOTAL; i += 1) {
            sparks.push({ x: rnd() * W, y: rnd() * H, r: 0.6 + 1.5 * rnd() * rnd(), c: STAR_RGBS[Math.floor(rnd() * STAR_RGBS.length)] });
        }
        const fog = document.createElement('canvas');
        fog.width = NEBULA_W;
        fog.height = NEBULA_H;
        const fogCtx = fog.getContext('2d');
        let seed = SEED;
        let t = 0;
        let reseedLeft = 0;
        let ox = 0;
        function sky() {
            return inp.idle < IDLE_TICKS ? (inp.x - W / 2) * 0.03 : Math.sin(t * 0.01) * 6;
        }
        const scene = {
            step() {
                t += 1;
                ox = lerp(ox, sky(), 0.08);
                if (reseedLeft > 0) {
                    reseedLeft -= 1;
                }
            },
            draw(ctx) {
                paintBg(ctx, 1);
                const phase = t * TWINKLE_SPEED;
                if (fogCtx) {
                    const img = fogCtx.createImageData(NEBULA_W, NEBULA_H);
                    for (let py = 0; py < NEBULA_H; py += 1) {
                        for (let px = 0; px < NEBULA_W; px += 1) {
                            const n1 = vnoise(px * 0.09 + phase * 0.6 + ox * 0.1, py * 0.09 - phase * 0.3, seed + 3);
                            const n2 = vnoise(px * 0.2 - phase, py * 0.2 + phase * 0.5, seed + 4);
                            const m = clamp(n1 * 0.75 + n2 * 0.35 - 0.2, 0, 1);
                            const c = mix([120, 168, 232], [186, 150, 255], vnoise(px * 0.05, py * 0.05, seed + 5));
                            const o = (py * NEBULA_W + px) * 4;
                            img.data[o] = c[0];
                            img.data[o + 1] = c[1];
                            img.data[o + 2] = c[2];
                            img.data[o + 3] = Math.round(255 * Math.pow(m, 1.6) * 0.75);
                        }
                    }
                    fogCtx.putImageData(img, 0, 0);
                    ctx.imageSmoothingEnabled = true;
                    ctx.drawImage(fog, 0, 0, W, H);
                }
                for (let i = 0; i < sparks.length; i += 1) {
                    const s = sparks[i];
                    // 느린 장(이웃이 닮는다)과 빠른 장(별마다 다르다)을 섞어 밝기를 정한다
                    const slow = vnoise(s.x * NOISE_SCALE + ox * 0.05, s.y * NOISE_SCALE + phase, seed);
                    const fast = vnoise(s.x * 0.5 + phase * 7, s.y * 0.5, seed + 1);
                    const v = slow * 0.65 + fast * 0.35;
                    const b = clamp(Math.pow(v * 1.6, CONTRAST), 0, 1);
                    if (b > 0.55) {
                        glow(ctx, s.x, s.y, 7 * s.r, s.c, 0.4 * b);
                    }
                    ctx.fillStyle = rgba(s.c, 0.12 + 0.88 * b);
                    ctx.beginPath();
                    ctx.arc(s.x, s.y, s.r * (0.7 + 0.5 * b), 0, PI2);
                    ctx.fill();
                }
            },
            label() {
                return reseedLeft > 0 ? TXT_RESEED : TXT_FIELD;
            },
            tap() {
                seed += 1;
                reseedLeft = 90;
            }
        };
        if (reduce) {
            for (let i = 0; i < 40; 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 "./SfNoiseTwinkleField.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';

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;

const BG: RGB = [14, 12, 32];
const STAR_RGBS: RGB[] = [[226, 238, 255], [255, 222, 196], [208, 196, 255], [196, 240, 228], [255, 206, 226]];

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;
    };
}
function glow(ctx: CanvasRenderingContext2D, x: number, y: number, r: number, c: RGB, a: number): void {
    const g = ctx.createRadialGradient(x, y, 0, x, y, r);
    g.addColorStop(0, rgba(c, a));
    g.addColorStop(1, rgba(c, 0));
    ctx.fillStyle = g;
    ctx.fillRect(x - r, y - r, r * 2, r * 2);
}
function paintBg(ctx: CanvasRenderingContext2D, alpha: number): void {
    ctx.fillStyle = rgba(BG, alpha);
    ctx.fillRect(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 NOISE_SCALE = 0.011;
const TWINKLE_SPEED = 0.035;
const CONTRAST = 2.6;
const SEED = 7;
const STAR_TOTAL = 360;
const NEBULA_W = 60;
const NEBULA_H = 38;
const TXT_FIELD = '노이즈 장 — 이웃 별이 함께 번진다';
const TXT_RESEED = '새 시드 — 같은 식, 다른 하늘';

interface Spark { x: number; y: number; r: number; c: RGB; }

// 격자 점의 값 — 정수 두 개와 시드를 섞어 0 이상 1 미만으로
function hash2(ix: number, iy: number, seed: number): number {
    let h = Math.imul(ix | 0, 374761393) + Math.imul(iy | 0, 668265263) + Math.imul(seed | 0, 1442695041);
    h = Math.imul(h ^ (h >>> 13), 1274126177);
    return ((h ^ (h >>> 16)) >>> 0) / 4294967296;
}
// 2차원 값 노이즈 — 네 격자 점을 부드럽게 보간
function vnoise(x: number, y: number, seed: number): number {
    const ix = Math.floor(x);
    const iy = Math.floor(y);
    const fx = smooth(x - ix);
    const fy = smooth(y - iy);
    return lerp(lerp(hash2(ix, iy, seed), hash2(ix + 1, iy, seed), fx), lerp(hash2(ix, iy + 1, seed), hash2(ix + 1, iy + 1, seed), fx), fy);
}

function makeScene(inp: Input, reduce: boolean): Scene {
    const rnd = lcg(450303);
    const sparks: Spark[] = [];
    for (let i = 0; i < STAR_TOTAL; i += 1) {
        sparks.push({ x: rnd() * W, y: rnd() * H, r: 0.6 + 1.5 * rnd() * rnd(), c: STAR_RGBS[Math.floor(rnd() * STAR_RGBS.length)] });
    }
    const fog = document.createElement('canvas');
    fog.width = NEBULA_W;
    fog.height = NEBULA_H;
    const fogCtx = fog.getContext('2d');
    let seed = SEED;
    let t = 0;
    let reseedLeft = 0;
    let ox = 0;
    function sky(): number {
        return inp.idle < IDLE_TICKS ? (inp.x - W / 2) * 0.03 : Math.sin(t * 0.01) * 6;
    }
    const scene: Scene = {
        step(): void {
            t += 1;
            ox = lerp(ox, sky(), 0.08);
            if (reseedLeft > 0) {
                reseedLeft -= 1;
            }
        },
        draw(ctx: CanvasRenderingContext2D): void {
            paintBg(ctx, 1);
            const phase = t * TWINKLE_SPEED;
            if (fogCtx) {
                const img = fogCtx.createImageData(NEBULA_W, NEBULA_H);
                for (let py = 0; py < NEBULA_H; py += 1) {
                    for (let px = 0; px < NEBULA_W; px += 1) {
                        const n1 = vnoise(px * 0.09 + phase * 0.6 + ox * 0.1, py * 0.09 - phase * 0.3, seed + 3);
                        const n2 = vnoise(px * 0.2 - phase, py * 0.2 + phase * 0.5, seed + 4);
                        const m = clamp(n1 * 0.75 + n2 * 0.35 - 0.2, 0, 1);
                        const c = mix([120, 168, 232], [186, 150, 255], vnoise(px * 0.05, py * 0.05, seed + 5));
                        const o = (py * NEBULA_W + px) * 4;
                        img.data[o] = c[0];
                        img.data[o + 1] = c[1];
                        img.data[o + 2] = c[2];
                        img.data[o + 3] = Math.round(255 * Math.pow(m, 1.6) * 0.75);
                    }
                }
                fogCtx.putImageData(img, 0, 0);
                ctx.imageSmoothingEnabled = true;
                ctx.drawImage(fog, 0, 0, W, H);
            }
            for (let i = 0; i < sparks.length; i += 1) {
                const s = sparks[i];
                // 느린 장(이웃이 닮는다)과 빠른 장(별마다 다르다)을 섞어 밝기를 정한다
                const slow = vnoise(s.x * NOISE_SCALE + ox * 0.05, s.y * NOISE_SCALE + phase, seed);
                const fast = vnoise(s.x * 0.5 + phase * 7, s.y * 0.5, seed + 1);
                const v = slow * 0.65 + fast * 0.35;
                const b = clamp(Math.pow(v * 1.6, CONTRAST), 0, 1);
                if (b > 0.55) {
                    glow(ctx, s.x, s.y, 7 * s.r, s.c, 0.4 * b);
                }
                ctx.fillStyle = rgba(s.c, 0.12 + 0.88 * b);
                ctx.beginPath();
                ctx.arc(s.x, s.y, s.r * (0.7 + 0.5 * b), 0, PI2);
                ctx.fill();
            }
        },
        label(): string {
            return reseedLeft > 0 ? TXT_RESEED : TXT_FIELD;
        },
        tap(): void {
            seed += 1;
            reseedLeft = 90;
        }
    };
    if (reduce) {
        for (let i = 0; i < 40; i += 1) {
            scene.step();
        }
    }
    return scene;
}

export default function SfNoiseTwinkleField() {
  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="노이즈 장이 별마다 다르게 반짝이게 하는 밤하늘" />
        <p className={styles.sc__status} ref={statusRef} aria-live="polite">노이즈 장 — 이웃 별이 함께 번진다</p>
        <button className={styles.sc__btn} ref={btnRef} type="button">멈춤</button>
        <p className={styles.sc__caption}>노이즈 장이 별마다 다르게 반짝이게 하는 밤하늘</p>
      </div>
    </main>
  );
}