03광원이 한 바퀴 돌며 달의 위상을 점으로 만드는 구체 셰이딩

<main class="stage">
<div class="sc is-demo" id="scRoot">
  <canvas class="sc__canvas" id="scCanvas" width="480" height="300" tabindex="0" aria-label="광원이 한 바퀴 돌며 달의 위상을 점으로 만드는 구체 셰이딩"></canvas>
  <p class="sc__status" id="scStatus" aria-live="polite">보름달 — 점이 가장 촘촘하다</p>
  <button class="sc__btn" id="scBtn" type="button">멈춤</button>
  <p class="sc__caption">광원이 한 바퀴 돌며 달의 위상을 점으로 만드는 구체 셰이딩</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 LIGHT_SPEED = 0.05;
    const SPHERE_R = 40;
    const AMBIENT = 0.04;
    const ATKINSON_KEEP = 0.125;
    const HALO_W = 9;
    const HALO_GAIN = 0.34;
    const DARK_03 = [36, 34, 56];
    const LIGHT_03 = [255, 244, 214];
    const TXT_FULL = '보름달 — 점이 가장 촘촘하다';
    const TXT_HALF = '반달 — 절반만 켜진다';
    const TXT_CRESCENT = '초승달 — 얇은 점의 띠';
    const TXT_NEW = '그믐 — 점이 거의 꺼진다';
    function makeScene(inp, reduce) {
        const buf = makeBuf();
        const err = new Float32Array(GW * GH);
        const dark = pack(DARK_03);
        const light = pack(LIGHT_03);
        const rnd = lcg(453303);
        const stars = [];
        for (let i = 0; i < 26; i += 1) {
            stars.push(Math.floor(rnd() * GW), Math.floor(rnd() * GH));
        }
        const sx = new Set();
        for (let i = 0; i < stars.length; i += 2) {
            sx.add(stars[i + 1] * GW + stars[i]);
        }
        const cx = GW / 2;
        const cy = GH / 2;
        let phi = 0;
        let dir = 1;
        function addErr(i, x, y, e) {
            if (x >= 0 && x < GW && y < GH) {
                err[i] += e;
            }
        }
        const scene = {
            step() {
                if (inp.idle < IDLE_TICKS) {
                    const target = (inp.x / W) * PI2;
                    const diff = Math.atan2(Math.sin(target - phi), Math.cos(target - phi));
                    phi += diff * 0.15;
                }
                else {
                    phi += LIGHT_SPEED * dir;
                }
            },
            draw(ctx) {
                // 광원 방향 — phi 가 0 이면 보는 쪽 정면, π 면 구 뒤쪽
                let lx = Math.sin(phi);
                let ly = 0.22;
                let lz = Math.cos(phi);
                const ln = Math.hypot(lx, ly, lz);
                lx /= ln;
                ly /= ln;
                lz /= ln;
                const lit = (1 + Math.cos(phi)) / 2;
                err.fill(0);
                for (let y = 0; y < GH; y += 1) {
                    for (let x = 0; x < GW; x += 1) {
                        const i = y * GW + x;
                        const dx = x + 0.5 - cx;
                        const dy = y + 0.5 - cy;
                        const r = Math.hypot(dx, dy);
                        let v = 0;
                        if (r < SPHERE_R) {
                            const nx = dx / SPHERE_R;
                            const ny = dy / SPHERE_R;
                            const nz = Math.sqrt(Math.max(0, 1 - nx * nx - ny * ny));
                            // 법선과 광원 방향의 내적이 곧 밝기
                            v = clamp(Math.max(0, nx * lx + ny * ly + nz * lz) + AMBIENT, 0, 1);
                        }
                        else {
                            v = HALO_GAIN * lit * Math.exp(-(r - SPHERE_R) / HALO_W);
                            if (sx.has(i) && r > SPHERE_R + 4) {
                                v = Math.max(v, 0.9);
                            }
                        }
                        const val = v + err[i];
                        const on = val > 0.5 ? 1 : 0;
                        buf.px[i] = on === 1 ? light : dark;
                        // Atkinson — 여섯 이웃이 오차의 1/8 씩만 받고 나머지는 버린다
                        const e = (val - on) * ATKINSON_KEEP;
                        addErr(i + 1, x + 1, y, e);
                        addErr(i + 2, x + 2, y, e);
                        if (y + 1 < GH) {
                            addErr(i + GW - 1, x - 1, y + 1, e);
                            addErr(i + GW, x, y + 1, e);
                            addErr(i + GW + 1, x + 1, y + 1, e);
                        }
                        if (y + 2 < GH) {
                            addErr(i + 2 * GW, x, y + 2, e);
                        }
                    }
                }
                flush(ctx, buf);
            },
            label() {
                const c = Math.cos(phi);
                if (c > 0.6) {
                    return TXT_FULL;
                }
                if (c > -0.1) {
                    return TXT_HALF;
                }
                return c > -0.7 ? TXT_CRESCENT : TXT_NEW;
            },
            tap() {
                dir = -dir;
            }
        };
        if (reduce) {
            for (let i = 0; i < 30; 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 "./DtLitSphereMoonPhase.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 LIGHT_SPEED = 0.05;
const SPHERE_R = 40;
const AMBIENT = 0.04;
const ATKINSON_KEEP = 0.125;
const HALO_W = 9;
const HALO_GAIN = 0.34;
const DARK_03: RGB = [36, 34, 56];
const LIGHT_03: RGB = [255, 244, 214];
const TXT_FULL = '보름달 — 점이 가장 촘촘하다';
const TXT_HALF = '반달 — 절반만 켜진다';
const TXT_CRESCENT = '초승달 — 얇은 점의 띠';
const TXT_NEW = '그믐 — 점이 거의 꺼진다';

function makeScene(inp: Input, reduce: boolean): Scene {
    const buf = makeBuf();
    const err = new Float32Array(GW * GH);
    const dark = pack(DARK_03);
    const light = pack(LIGHT_03);
    const rnd = lcg(453303);
    const stars: number[] = [];
    for (let i = 0; i < 26; i += 1) {
        stars.push(Math.floor(rnd() * GW), Math.floor(rnd() * GH));
    }
    const sx = new Set<number>();
    for (let i = 0; i < stars.length; i += 2) {
        sx.add(stars[i + 1] * GW + stars[i]);
    }
    const cx = GW / 2;
    const cy = GH / 2;
    let phi = 0;
    let dir = 1;
    function addErr(i: number, x: number, y: number, e: number): void {
        if (x >= 0 && x < GW && y < GH) {
            err[i] += e;
        }
    }
    const scene: Scene = {
        step(): void {
            if (inp.idle < IDLE_TICKS) {
                const target = (inp.x / W) * PI2;
                const diff = Math.atan2(Math.sin(target - phi), Math.cos(target - phi));
                phi += diff * 0.15;
            } else {
                phi += LIGHT_SPEED * dir;
            }
        },
        draw(ctx: CanvasRenderingContext2D): void {
            // 광원 방향 — phi 가 0 이면 보는 쪽 정면, π 면 구 뒤쪽
            let lx = Math.sin(phi);
            let ly = 0.22;
            let lz = Math.cos(phi);
            const ln = Math.hypot(lx, ly, lz);
            lx /= ln;
            ly /= ln;
            lz /= ln;
            const lit = (1 + Math.cos(phi)) / 2;
            err.fill(0);
            for (let y = 0; y < GH; y += 1) {
                for (let x = 0; x < GW; x += 1) {
                    const i = y * GW + x;
                    const dx = x + 0.5 - cx;
                    const dy = y + 0.5 - cy;
                    const r = Math.hypot(dx, dy);
                    let v = 0;
                    if (r < SPHERE_R) {
                        const nx = dx / SPHERE_R;
                        const ny = dy / SPHERE_R;
                        const nz = Math.sqrt(Math.max(0, 1 - nx * nx - ny * ny));
                        // 법선과 광원 방향의 내적이 곧 밝기
                        v = clamp(Math.max(0, nx * lx + ny * ly + nz * lz) + AMBIENT, 0, 1);
                    } else {
                        v = HALO_GAIN * lit * Math.exp(-(r - SPHERE_R) / HALO_W);
                        if (sx.has(i) && r > SPHERE_R + 4) {
                            v = Math.max(v, 0.9);
                        }
                    }
                    const val = v + err[i];
                    const on = val > 0.5 ? 1 : 0;
                    buf.px[i] = on === 1 ? light : dark;
                    // Atkinson — 여섯 이웃이 오차의 1/8 씩만 받고 나머지는 버린다
                    const e = (val - on) * ATKINSON_KEEP;
                    addErr(i + 1, x + 1, y, e);
                    addErr(i + 2, x + 2, y, e);
                    if (y + 1 < GH) {
                        addErr(i + GW - 1, x - 1, y + 1, e);
                        addErr(i + GW, x, y + 1, e);
                        addErr(i + GW + 1, x + 1, y + 1, e);
                    }
                    if (y + 2 < GH) {
                        addErr(i + 2 * GW, x, y + 2, e);
                    }
                }
            }
            flush(ctx, buf);
        },
        label(): string {
            const c = Math.cos(phi);
            if (c > 0.6) {
                return TXT_FULL;
            }
            if (c > -0.1) {
                return TXT_HALF;
            }
            return c > -0.7 ? TXT_CRESCENT : TXT_NEW;
        },
        tap(): void {
            dir = -dir;
        }
    };
    if (reduce) {
        for (let i = 0; i < 30; i += 1) {
            scene.step();
        }
    }
    return scene;
}

export default function DtLitSphereMoonPhase() {
  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="광원이 한 바퀴 돌며 달의 위상을 점으로 만드는 구체 셰이딩" />
        <p className={styles.sc__status} ref={statusRef} aria-live="polite">보름달 — 점이 가장 촘촘하다</p>
        <button className={styles.sc__btn} ref={btnRef} type="button">멈춤</button>
        <p className={styles.sc__caption}>광원이 한 바퀴 돌며 달의 위상을 점으로 만드는 구체 셰이딩</p>
      </div>
    </main>
  );
}