04Fire spread — a consumption rule that burns neighboring fuel and shrinks

<main class="stage">
<div class="cd is-demo" id="cdRoot">
  <p class="cd__hint"><span>Fire ignites neighboring trees with a probability, then itself turns to ash</span></p>
  <div class="cd__field" id="cdField" role="application" aria-label="Fire Spread cellular automaton demo" tabindex="0">
    <canvas class="cd__cv" id="cdCv"></canvas>
  </div>
  <div class="cd__bar">
    <span class="cd__meta"><b class="cd__val" id="cdN">6</b>% ignition chance</span>
    <span class="cd__meta cd__meta--dim">canvas · ImageData · requestAnimationFrame</span>
  </div>
</div>
</main>

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

// 불 번짐 소모 규칙(04). @keyframes 를 아예 두지 않는다 —
// 움직임은 전부 캔버스 rAF 루프(셀 오토마타 점화·수명·연기)가 만든다.
// 무대는 모래의 밤. 파스텔 고정 팔레트 16색을 --sand-* 로 편 공통 규격(318 전 항목 동일).

$duration: $dur-loop;
$easing: $ease-spring;
$color: $subject-lilac;

@include stage($stage-ink);

// ── 편 공통 파스텔 팔레트(BD26 vivid 0 실측 통과값 — 다른 색 금지) ──
$sand-night: #201c17;   // 무대 — 모래의 밤
$sand-mist:  #d8d2c6;   // 보조 글자·안개 먼지
$sand-glow:  #f2e2c4;   // 잔광 — 화면을 도는 옅은 달빛
$sand-grain: #d9b98a;
$sand-gold:  #ecd9b0;   // 불 하이라이트 — 골드
$sand-water: #a9c8dd;
$sand-ice:   #cfe3ee;
$sand-fire:  #ffc9ad;   // 불 — 파스텔 화염
$sand-flame: #ffe0c4;   // 플레임 — 밝은 속살
$sand-ash:   #b9b2a6;   // 재
$sand-smoke: #8e8879;   // 연기
$sand-plant: #9fd6ad;
$sand-leaf:  #c4e6c9;
$sand-acid:  #c7dd8f;
$sand-stone: #8a8578;
$sand-wood:  #b98a63;   // 나무 — 연료

.cd {
  // 렌더러가 읽는 색 — JS 는 getComputedStyle 로 --sand-* 를 받아 쓴다
  --sand-night: #{$sand-night};
  --sand-mist:  #{$sand-mist};
  --sand-glow:  #{$sand-glow};
  --sand-grain: #{$sand-grain};
  --sand-gold:  #{$sand-gold};
  --sand-water: #{$sand-water};
  --sand-ice:   #{$sand-ice};
  --sand-fire:  #{$sand-fire};
  --sand-flame: #{$sand-flame};
  --sand-ash:   #{$sand-ash};
  --sand-smoke: #{$sand-smoke};
  --sand-plant: #{$sand-plant};
  --sand-leaf:  #{$sand-leaf};
  --sand-acid:  #{$sand-acid};
  --sand-stone: #{$sand-stone};
  --sand-wood:  #{$sand-wood};

  display: flex; flex-direction: column; gap: $sp-2;
  width: 100%; max-width: 424px;
}

.cd__hint {
  display: flex; align-items: center; gap: $sp-1; margin: 0;
  font-weight: 700; font-size: clamp(10px, 2.8vw, 12px); line-height: 1.35;
  color: $sand-mist;                        // 밤 무대 위 — 먼지 톤 글자
}

.cd__field {
  position: relative; height: 200px;
  border-radius: $r-card; overflow: hidden;
  background: $sand-night;
  box-shadow: inset 0 0 0 1px rgba($sand-mist, .18);
}
.cd__field:focus-visible { outline: 2px solid $subject-lilac; outline-offset: 2px; }

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

.cd__bar { display: flex; align-items: baseline; justify-content: space-between; gap: $sp-2; }
.cd__meta { font-size: 10px; font-weight: 500; color: rgba($sand-mist, .72); }
.cd__val { color: $subject-lilac; font-weight: 700; }     // 밤 위 라일락 라벨
.cd__meta--dim { font-size: 10px; }

@media (max-width: 340px) {
  .cd { gap: $sp-1; }
  .cd__field { height: 110px; }
  .cd__meta--dim { display: none; }
}

// reduce — rAF 를 돌리지 않고 점화 직후의 한 장만 남는다.
@media (prefers-reduced-motion: reduce) {
  .cd.is-still .cd__field { cursor: default !important; }
}

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);
}

.cd {
  --sand-night: #201c17;
  --sand-mist: #d8d2c6;
  --sand-glow: #f2e2c4;
  --sand-grain: #d9b98a;
  --sand-gold: #ecd9b0;
  --sand-water: #a9c8dd;
  --sand-ice: #cfe3ee;
  --sand-fire: #ffc9ad;
  --sand-flame: #ffe0c4;
  --sand-ash: #b9b2a6;
  --sand-smoke: #8e8879;
  --sand-plant: #9fd6ad;
  --sand-leaf: #c4e6c9;
  --sand-acid: #c7dd8f;
  --sand-stone: #8a8578;
  --sand-wood: #b98a63;
  display: flex;
  flex-direction: column;
  gap: 8px;
  width: 100%;
  max-width: 424px;
}

.cd__hint {
  display: flex;
  align-items: center;
  gap: 4px;
  margin: 0;
  font-weight: 700;
  font-size: clamp(10px, 2.8vw, 12px);
  line-height: 1.35;
  color: #d8d2c6;
}

.cd__field {
  position: relative;
  height: 200px;
  border-radius: 16px;
  overflow: hidden;
  background: #201c17;
  box-shadow: inset 0 0 0 1px rgba(216, 210, 198, 0.18);
}

.cd__field:focus-visible {
  outline: 2px solid #b9a0ff;
  outline-offset: 2px;
}

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

.cd__bar {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 8px;
}

.cd__meta {
  font-size: 10px;
  font-weight: 500;
  color: rgba(216, 210, 198, 0.72);
}

.cd__val {
  color: #b9a0ff;
  font-weight: 700;
}

.cd__meta--dim {
  font-size: 10px;
}

@media (max-width: 340px) {
  .cd {
    gap: 4px;
  }
  .cd__field {
    height: 110px;
  }
  .cd__meta--dim {
    display: none;
  }
}
@media (prefers-reduced-motion: reduce) {
  .cd.is-still .cd__field {
    cursor: default !important;
  }
}

// 불 번짐(04). 재료 코드 0 빈칸 1 모래 2 물 3 벽 4 나무 5 불 6 재 7 연기 8 씨앗 9 식물 10 흙 11 돌.
// 불 칸은 매 틱 이웃(4방향) 나무·기름(밝은 fire 색 조명 나무) 칸을 IGNITE_P 확률로 불로 바꾸고,
// 자신은 LIFE 틱의 수명이 다하면 재가 된 뒤 위로 연기를 몇 칸 보낸다 — 타고 넘어가며 꺼지는 불줄기.
(function () {
  // ── 변형 상수 블록 — 아래 값 하나만 바꿔 변형을 만든다 ──
  var IGNITE_P = 0.06;  // 이웃 점화 확률 — 0.02 는 느린 은은한 불씨, 0.14 는 폭발적 화염
  var LIFE     = 14;    // 불 수명(틱) — 짧으면 잔불 없이 스치듯, 길면 오래 타오른다
  // ────────────────────────────────────────────────────

  var EMPTY=0, WOOD=4, FIRE=5, ASH=6, SMOKE=7, OIL=8;
  var root = document.getElementById('cdRoot');
  var field = document.getElementById('cdField');
  var cv = document.getElementById('cdCv');
  var ctx = cv.getContext('2d');
  var nOut = document.getElementById('cdN');

  // 시드 고정 PRNG — mulberry32. 미리보기가 항상 같은 연소 순서로 흐른다
  function makeRand(seed) {
    var st = seed >>> 0;
    return function () {
      st = (st + 0x6D2B79F5) >>> 0;
      var t = st;
      t = Math.imul(t ^ (t >>> 15), t | 1);
      t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
      return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
    };
  }
  var rand = makeRand(0x318A44);

  // 색은 CSS 커스텀 프로퍼티(--sand-*)에서 getComputedStyle 로 읽는다 — 파스텔 토큰이 scss 한 곳에
  var css = getComputedStyle(root);
  function tokRGB(name) {
    var s = css.getPropertyValue(name).trim();
    var hx = s.length === 4
      ? s.charAt(1) + s.charAt(1) + s.charAt(2) + s.charAt(2) + s.charAt(3) + s.charAt(3)
      : s.slice(1);
    return [parseInt(hx.slice(0, 2), 16), parseInt(hx.slice(2, 4), 16), parseInt(hx.slice(4, 6), 16)];
  }
  var C_NIGHT = tokRGB('--sand-night');
  var C_GLOW  = tokRGB('--sand-glow');
  var C_FIRE  = tokRGB('--sand-fire');
  var C_FLAME = tokRGB('--sand-flame');
  var C_GOLD  = tokRGB('--sand-gold');
  var C_ASH   = tokRGB('--sand-ash');
  var C_SMOKE = tokRGB('--sand-smoke');
  var C_WOOD  = tokRGB('--sand-wood');
  var C_MIST  = tokRGB('--sand-mist');

  var TAU = Math.PI * 2;
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var W = 0, H = 0, cols = 0, rows = 0, CELL = 4;
  var grid = null, life = null, img = null, buf = null;
  var raf = 0, t0 = -1;
  var tick = 0;

  // ── 장면 — 계단식 나무 발판 3단 + 바닥 기름 웅덩이 ──
  // 오일은 '밝은 fire 색조로 조명된 나무' — 가연물이되 셀 색만 fire 톤으로 둔다(기름 표면의 광택)
  function idx(x, y) { return y * cols + x; }
  function build() {
    grid = new Uint8Array(cols * rows);
    life = new Uint8Array(cols * rows);
    var x, y, i;
    // 계단식 나무 발판 3단 — 좌하단에서 우상단으로 올라가는 층
    var rowsPer = Math.max(2, Math.round(rows * 0.05));
    var y0 = rows - Math.max(2, Math.round(rows * 0.16));
    for (var step = 0; step < 3; step++) {
      var x0 = Math.round(cols * (0.06 + step * 0.24));
      var x1 = Math.round(cols * (0.30 + step * 0.24));
      var yy = y0 - step * Math.round(rows * 0.16);
      for (x = x0; x < x1; x++)
        for (y = yy; y < yy + rowsPer; y++)
          if (x >= 0 && x < cols && y >= 0 && y < rows) grid[idx(x, y)] = WOOD;
    }
    // 바닥 기름 웅덩이 — 맨 아래 2줄 전체 폭
    for (x = 0; x < cols; x++)
      for (y = rows - 2; y < rows; y++)
        grid[idx(x, y)] = OIL;
    img = ctx.createImageData(cols, rows);
    buf = img.data;
  }

  // ── 점화 스케줄 — t=0 첫 나무, 이후 ~1.2초마다 다른 위치(우측 발판 → 기름) 재점화 ──
  var ignitions = [];
  function scheduleIgnitions() {
    ignitions = [
      { at: 0.05, kind: 'wood1' },
      { at: 1.2,  kind: 'wood3' },
      { at: 2.4,  kind: 'oil' },
      { at: 3.6,  kind: 'wood2' },
      { at: 4.8,  kind: 'oil' },
      { at: 6.0,  kind: 'wood1' },
      { at: 7.2,  kind: 'wood3' },
      { at: 8.4,  kind: 'oil' }
    ];
  }
  var ignIdx = 0;
  function doIgnite(kind) {
    var y0 = rows - Math.max(2, Math.round(rows * 0.16));
    var rowsPer = Math.max(2, Math.round(rows * 0.05));
    function spark(cx, top, w, h, mat) {
      // 해당 재료 영역에서 무작위 한 칸을 찾아 불로
      for (var k = 0; k < 60; k++) {
        var x = cx + Math.floor(rand() * w);
        var y = top + Math.floor(rand() * h);
        if (x < 0 || x >= cols || y < 0 || y >= rows) continue;
        var i = idx(x, y);
        if (grid[i] === mat) { grid[i] = FIRE; life[i] = LIFE; return true; }
      }
      return false;
    }
    if (kind === 'wood1') spark(Math.round(cols * 0.10), y0, Math.round(cols * 0.22), rowsPer, WOOD);
    else if (kind === 'wood2') spark(Math.round(cols * 0.34), y0 - Math.round(rows * 0.16), Math.round(cols * 0.22), rowsPer, WOOD);
    else if (kind === 'wood3') spark(Math.round(cols * 0.58), y0 - Math.round(rows * 0.32), Math.round(cols * 0.22), rowsPer, WOOD);
    else spark(Math.round(cols * 0.1), rows - 2, Math.round(cols * 0.8), 2, OIL);
  }

  function update() {
    tick++;
    // 아래 행 → 위 행. 이미 이번 틱에 갱신된 칸은 건너뛴다(불의 연쇄가 한 틱에 끝까지 달리는 것 방지)
    var moved = new Uint8Array(cols * rows);
    var x, y, i, d;
    for (y = rows - 1; y >= 0; y--) {
      var ltr = (tick & 1) === 0; // 홀짝 스캔 방향 교차 — 번짐 비대칭 방지
      for (var s = 0; s < cols; s++) {
        x = ltr ? s : cols - 1 - s;
        i = idx(x, y);
        if (moved[i]) continue;
        var m = grid[i];
        if (m === FIRE) {
          // 이웃 점화 — 4방향의 나무·기름을 확률로 불로
          var nb = [[1,0],[-1,0],[0,1],[0,-1]];
          for (d = 0; d < 4; d++) {
            var nx = x + nb[d][0], ny = y + nb[d][1];
            if (nx < 0 || nx >= cols || ny < 0 || ny >= rows) continue;
            var j = idx(nx, ny);
            if ((grid[j] === WOOD || grid[j] === OIL) && rand() < IGNITE_P) {
              grid[j] = FIRE; life[j] = LIFE; moved[j] = 1;
            }
          }
          // 수명 감소 — 다하면 재, 위 빈칸에 연기 시도
          if (life[i] <= 1) {
            grid[i] = ASH;
            if (y > 0 && grid[idx(x, y - 1)] === EMPTY && rand() < 0.5) {
              grid[idx(x, y - 1)] = SMOKE;
              if (y > 1 && grid[idx(x, y - 2)] === EMPTY && rand() < 0.5) grid[idx(x, y - 2)] = SMOKE;
            }
          } else {
            life[i]--;
          }
        } else if (m === SMOKE) {
          // 연기 — 위로 한 칸, 막히면 옆. 오래 남지 않게 확률 소멸
          if (rand() < 0.22) { grid[i] = EMPTY; continue; }
          var up = y > 0 ? idx(x, y - 1) : -1;
          if (up >= 0 && grid[up] === EMPTY) {
            grid[up] = SMOKE; grid[i] = EMPTY; moved[up] = 1;
          } else if (x > 0 && grid[idx(x - 1, y)] === EMPTY && rand() < 0.5) {
            grid[idx(x - 1, y)] = SMOKE; grid[i] = EMPTY;
          } else if (x < cols - 1 && grid[idx(x + 1, y)] === EMPTY && rand() < 0.5) {
            grid[idx(x + 1, y)] = SMOKE; grid[i] = EMPTY;
          }
        } else if (m === ASH) {
          // 재 — 낙하(아래 빈칸) + 확률 소멸. 소멸한 자리는 연기 없이 비운다
          if (y < rows - 1 && grid[idx(x, y + 1)] === EMPTY) {
            grid[idx(x, y + 1)] = ASH; grid[i] = EMPTY; moved[idx(x, y + 1)] = 1;
          } else if (rand() < 0.012) { grid[i] = EMPTY; }
        }
      }
    }
  }

  // ── 렌더 — ImageData 버퍼 → putImageData. 1 픽셀 = 1 칸 ──
  function px(o, c, k) {
    buf[o]     = c[0] * k;
    buf[o + 1] = c[1] * k;
    buf[o + 2] = c[2] * k;
    buf[o + 3] = 255;
  }
  function draw(t) {
    var x, y, i, o;
    // 배경 — 밤. 칸 단위로 밤색을 깔아 ImageData 전체를 채운다
    for (i = 0; i < cols * rows; i++) {
      o = i * 4;
      buf[o] = C_NIGHT[0]; buf[o + 1] = C_NIGHT[1]; buf[o + 2] = C_NIGHT[2]; buf[o + 3] = 255;
    }
    // 격자 재료 렌더
    var flicker = 0.5 + 0.5 * Math.sin(t * 9.3) * Math.cos(t * 6.1);
    for (y = 0; y < rows; y++) {
      for (x = 0; x < cols; x++) {
        i = idx(x, y);
        o = i * 4;
        var m = grid[i];
        if (m === WOOD) px(o, C_WOOD, 1);
        else if (m === OIL) px(o, C_FIRE, 0.9);
        else if (m === ASH) px(o, C_ASH, 0.95);
        else if (m === SMOKE) px(o, C_SMOKE, 0.8);
        else if (m === FIRE) {
          // 매 틱 fire/flame/gold 랜덤 스왑 — 타오르는 질감
          var r3 = rand();
          var fc = r3 < 0.4 ? C_FIRE : (r3 < 0.8 ? C_FLAME : C_GOLD);
          px(o, fc, 0.85 + 0.3 * flicker);
        }
      }
    }
    ctx.putImageData(img, 0, 0);

    // 잔광(안개) — 중심이 sin/cos 로 천천히 도는 radial gradient, 알파 낮게 — 화면이 늘 살아 있다
    var gx = W * (0.5 + 0.30 * Math.sin(t * 0.9));
    var gy = H * (0.55 + 0.26 * Math.cos(t * 0.7));
    var gr = Math.max(W, H) * 0.52;
    var g = ctx.createRadialGradient(gx, gy, 0, gx, gy, gr);
    g.addColorStop(0, 'rgba(' + C_GLOW.join(',') + ',0.07)');
    g.addColorStop(1, 'rgba(' + C_GLOW.join(',') + ',0)');
    ctx.fillStyle = g;
    ctx.fillRect(0, 0, W, H);
  }

  function fit() {
    var r = field.getBoundingClientRect();
    W = r.width; H = r.height;
    cv.width = Math.round(W); cv.height = Math.round(H);
    cols = Math.max(8, Math.floor(W / CELL));
    rows = Math.max(8, Math.floor(H / CELL));
    build();
    scheduleIgnitions();
    ignIdx = 0;
    tick = 0;
  }

  function stillFrame() {
    // reduce — 점화 직후 몇 틱만 돌리고 한 장
    doIgnite('wood1');
    for (var k = 0; k < 12; k++) update();
    draw(0.2);
  }

  var STEP = 1000 / 60, acc = 0;
  function frame(now) {
    if (t0 < 0) t0 = now;
    var dt = now - t0;
    acc = acc + (now - (frame.prev || now));
    frame.prev = now;
    while (acc >= STEP) {
      update();
      var t = tick / 60;
      while (ignIdx < ignitions.length && ignitions[ignIdx].at <= t) {
        doIgnite(ignitions[ignIdx].kind);
        ignIdx++;
      }
      acc -= STEP;
    }
    draw(dt / 1000);
    raf = requestAnimationFrame(frame);
  }

  window.addEventListener('resize', function () {
    fit();
    if (reduce) stillFrame();
  });

  fit();
  nOut.textContent = String(Math.round(IGNITE_P * 100));
  if (reduce) {
    stillFrame();
    root.classList.add('is-still');
  } else {
    raf = requestAnimationFrame(frame);
  }
})();

// FireBurnSpread — vanilla 판(run/318/demo/04-sand-fire-burn-spread/index.html) 의 React 포트.
// 불 번짐 소모 규칙 — 불 칸은 이웃 나무·기름을 확률로 점화하고 수명이 다하면 재가 되며 연기를 남긴다.
// 계단식 나무 발판 3단 + 바닥 기름 웅덩이를 ~1.2초마다 다른 위치에서 재점화해 화면이 늘 활동한다.
import { useEffect, useRef, useState } from "react";
import type { CSSProperties } from "react";
import styles from "./FireBurnSpread.module.scss";

export type FireBurnSpreadProps = {
  duration?: string;
  easing?: string;
  color?: string;
  igniteP?: number;   // 이웃 점화 확률 — 변형 "점화 확률" 축(0.02 은은 · 0.14 폭발)
  life?: number;      // 불 수명(틱)
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
type Box<T> = { current: T };
type RGB = [number, number, number];
type Ignition = { at: number; kind: string };
type Colors = {
  night: RGB; glow: RGB; fire: RGB; flame: RGB; gold: RGB;
  ash: RGB; smoke: RGB; wood: RGB;
};

const TAU = Math.PI * 2;
const FIELD_LABEL = "불 번짐 셀 오토마타 데모";
const EMPTY = 0, WOOD = 4, FIRE = 5, ASH = 6, SMOKE = 7, OIL = 8;
const CELL = 4;
const STEP = 1000 / 60;

// 시드 고정 PRNG — mulberry32. 미리보기가 항상 같은 연소 순서로 흐른다
function makePRNG(seed: number): () => number {
  let s = seed >>> 0;
  return function () {
    s = (s + 0x6d2b79f5) >>> 0;
    let t = s;
    t = Math.imul(t ^ (t >>> 15), t | 1);
    t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
    return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
  };
}

export default function FireBurnSpread({
  duration = "2s",
  easing = "cubic-bezier(.2, .8, .2, 1)",
  color = "#b9a0ff",
  igniteP = 0.06,
  life = 14,
}: FireBurnSpreadProps) {
  const rootRef = useRef<HTMLDivElement | null>(null);
  const fieldRef = useRef<HTMLDivElement | null>(null);
  const cvRef = useRef<HTMLCanvasElement | null>(null);
  const ctxRef = useRef<CanvasRenderingContext2D | null>(null);
  const sizeRef = useRef({ w: 0, h: 0 }) as Box<{ w: number; h: number }>;
  const colRef = useRef<Colors | null>(null);
  const ignitePRef = useRef(igniteP) as Box<number>;
  const lifeRef = useRef(life) as Box<number>;
  const gridRef = useRef<Uint8Array | null>(null) as Box<Uint8Array | null>;
  const lifeGridRef = useRef<Uint8Array | null>(null) as Box<Uint8Array | null>;
  const imgRef = useRef<ImageData | null>(null) as Box<ImageData | null>;
  const dimsRef = useRef({ cols: 0, rows: 0 }) as Box<{ cols: number; rows: number }>;
  const tickRef = useRef(0) as Box<number>;
  const ignRef = useRef<Ignition[]>([]) as Box<Ignition[]>;
  const ignIdxRef = useRef(0) as Box<number>;
  const rafRef = useRef(0) as Box<number>;
  const randRef = useRef(makePRNG(0x318a44)) as Box<() => number>;
  const [n, setN] = useState(String(Math.round(igniteP * 100)));
  const [still, setStill] = useState(false);
  const vars: Vars = { "--duration": duration, "--easing": easing, "--color": color };

  function reduced(): boolean {
    return window.matchMedia("(prefers-reduced-motion: reduce)").matches;
  }

  // 색은 CSS 커스텀 프로퍼티(--sand-*)에서 getComputedStyle 로 읽는다 — 파스텔 토큰이 scss 한 곳에
  function tokRGB(root: HTMLDivElement, name: string): RGB {
    const s = getComputedStyle(root).getPropertyValue(name).trim();
    const hx = s.length === 4
      ? s.charAt(1) + s.charAt(1) + s.charAt(2) + s.charAt(2) + s.charAt(3) + s.charAt(3)
      : s.slice(1);
    return [parseInt(hx.slice(0, 2), 16), parseInt(hx.slice(2, 4), 16), parseInt(hx.slice(4, 6), 16)];
  }

  function idx(x: number, y: number): number {
    const { cols } = dimsRef.current;
    return y * cols + x;
  }

  // ── 장면 — 계단식 나무 발판 3단 + 바닥 기름 웅덩이 ──
  // 오일은 '밝은 fire 색조로 조명된 나무' — 가연물이되 셀 색만 fire 톤으로 둔다(기름 표면의 광택)
  function build(): void {
    const { cols, rows } = dimsRef.current;
    const grid = new Uint8Array(cols * rows);
    const lifeGrid = new Uint8Array(cols * rows);
    const rowsPer = Math.max(2, Math.round(rows * 0.05));
    const y0 = rows - Math.max(2, Math.round(rows * 0.16));
    for (let step = 0; step < 3; step++) {
      const x0 = Math.round(cols * (0.06 + step * 0.24));
      const x1 = Math.round(cols * (0.3 + step * 0.24));
      const yy = y0 - step * Math.round(rows * 0.16);
      for (let x = x0; x < x1; x++)
        for (let y = yy; y < yy + rowsPer; y++)
          if (x >= 0 && x < cols && y >= 0 && y < rows) grid[idx(x, y)] = WOOD;
    }
    for (let x = 0; x < cols; x++)
      for (let y = rows - 2; y < rows; y++)
        grid[idx(x, y)] = OIL;
    gridRef.current = grid;
    lifeGridRef.current = lifeGrid;
    const ctx = ctxRef.current;
    if (ctx) imgRef.current = ctx.createImageData(cols, rows);
  }

  // ── 점화 스케줄 — t=0 첫 나무, 이후 ~1.2초마다 다른 위치(우측 발판 → 기름) 재점화 ──
  function scheduleIgnitions(): void {
    ignRef.current = [
      { at: 0.05, kind: "wood1" },
      { at: 1.2, kind: "wood3" },
      { at: 2.4, kind: "oil" },
      { at: 3.6, kind: "wood2" },
      { at: 4.8, kind: "oil" },
      { at: 6.0, kind: "wood1" },
      { at: 7.2, kind: "wood3" },
      { at: 8.4, kind: "oil" },
    ];
    ignIdxRef.current = 0;
  }

  function doIgnite(kind: string): void {
    if (!gridRef.current || !lifeGridRef.current) return;
    const grid: Uint8Array = gridRef.current;
    const lifeGrid: Uint8Array = lifeGridRef.current;
    const { cols, rows } = dimsRef.current;
    const rand = randRef.current;
    const y0 = rows - Math.max(2, Math.round(rows * 0.16));
    const rowsPer = Math.max(2, Math.round(rows * 0.05));
    function spark(cx: number, top: number, w: number, h: number, mat: number): void {
      for (let k = 0; k < 60; k++) {
        const x = cx + Math.floor(rand() * w);
        const y = top + Math.floor(rand() * h);
        if (x < 0 || x >= cols || y < 0 || y >= rows) continue;
        const i = idx(x, y);
        if (grid[i] === mat) { grid[i] = FIRE; lifeGrid[i] = lifeRef.current; return; }
      }
    }
    if (kind === "wood1") spark(Math.round(cols * 0.1), y0, Math.round(cols * 0.22), rowsPer, WOOD);
    else if (kind === "wood2") spark(Math.round(cols * 0.34), y0 - Math.round(rows * 0.16), Math.round(cols * 0.22), rowsPer, WOOD);
    else if (kind === "wood3") spark(Math.round(cols * 0.58), y0 - Math.round(rows * 0.32), Math.round(cols * 0.22), rowsPer, WOOD);
    else spark(Math.round(cols * 0.1), rows - 2, Math.round(cols * 0.8), 2, OIL);
  }

  function update(): void {
    const grid = gridRef.current;
    const lifeGrid = lifeGridRef.current;
    const { cols, rows } = dimsRef.current;
    const rand = randRef.current;
    if (!grid || !lifeGrid) return;
    tickRef.current++;
    const tick = tickRef.current;
    const moved = new Uint8Array(cols * rows);
    for (let y = rows - 1; y >= 0; y--) {
      const ltr = (tick & 1) === 0; // 홀짝 스캔 방향 교차 — 번짐 비대칭 방지
      for (let s = 0; s < cols; s++) {
        const x = ltr ? s : cols - 1 - s;
        const i = idx(x, y);
        if (moved[i]) continue;
        const m = grid[i];
        if (m === FIRE) {
          // 이웃 점화 — 4방향의 나무·기름을 확률로 불로
          const nb = [[1, 0], [-1, 0], [0, 1], [0, -1]];
          for (let d = 0; d < 4; d++) {
            const nx = x + nb[d][0], ny = y + nb[d][1];
            if (nx < 0 || nx >= cols || ny < 0 || ny >= rows) continue;
            const j = idx(nx, ny);
            if ((grid[j] === WOOD || grid[j] === OIL) && rand() < ignitePRef.current) {
              grid[j] = FIRE; lifeGrid[j] = lifeRef.current; moved[j] = 1;
            }
          }
          // 수명 감소 — 다하면 재, 위 빈칸에 연기 시도
          if (lifeGrid[i] <= 1) {
            grid[i] = ASH;
            if (y > 0 && grid[idx(x, y - 1)] === EMPTY && rand() < 0.5) {
              grid[idx(x, y - 1)] = SMOKE;
              if (y > 1 && grid[idx(x, y - 2)] === EMPTY && rand() < 0.5) grid[idx(x, y - 2)] = SMOKE;
            }
          } else {
            lifeGrid[i]--;
          }
        } else if (m === SMOKE) {
          // 연기 — 위로 한 칸, 막히면 옆. 오래 남지 않게 확률 소멸
          if (rand() < 0.22) { grid[i] = EMPTY; continue; }
          const up = y > 0 ? idx(x, y - 1) : -1;
          if (up >= 0 && grid[up] === EMPTY) {
            grid[up] = SMOKE; grid[i] = EMPTY; moved[up] = 1;
          } else if (x > 0 && grid[idx(x - 1, y)] === EMPTY && rand() < 0.5) {
            grid[idx(x - 1, y)] = SMOKE; grid[i] = EMPTY;
          } else if (x < cols - 1 && grid[idx(x + 1, y)] === EMPTY && rand() < 0.5) {
            grid[idx(x + 1, y)] = SMOKE; grid[i] = EMPTY;
          }
        } else if (m === ASH) {
          // 재 — 낙하(아래 빈칸) + 확률 소멸. 소멸한 자리는 연기 없이 비운다
          if (y < rows - 1 && grid[idx(x, y + 1)] === EMPTY) {
            grid[idx(x, y + 1)] = ASH; grid[i] = EMPTY; moved[idx(x, y + 1)] = 1;
          } else if (rand() < 0.012) { grid[i] = EMPTY; }
        }
      }
    }
  }

  // ── 렌더 — ImageData 버퍼 → putImageData. 1 픽셀 = 1 칸 ──
  function px(buf: Uint8ClampedArray, o: number, c: RGB, k: number): void {
    buf[o] = c[0] * k;
    buf[o + 1] = c[1] * k;
    buf[o + 2] = c[2] * k;
    buf[o + 3] = 255;
  }

  function draw(t: number): void {
    const ctx = ctxRef.current;
    const col = colRef.current;
    const img = imgRef.current;
    const grid = gridRef.current;
    const { w: W, h: H } = sizeRef.current;
    const { cols, rows } = dimsRef.current;
    const rand = randRef.current;
    if (!ctx || !col || !img || !grid) return;
    const buf = img.data;
    let i: number, o: number;
    for (i = 0; i < cols * rows; i++) {
      o = i * 4;
      buf[o] = col.night[0]; buf[o + 1] = col.night[1]; buf[o + 2] = col.night[2]; buf[o + 3] = 255;
    }
    const flicker = 0.5 + 0.5 * Math.sin(t * 9.3) * Math.cos(t * 6.1);
    for (let y = 0; y < rows; y++) {
      for (let x = 0; x < cols; x++) {
        i = idx(x, y);
        o = i * 4;
        const m = grid[i];
        if (m === WOOD) px(buf, o, col.wood, 1);
        else if (m === OIL) px(buf, o, col.fire, 0.9);
        else if (m === ASH) px(buf, o, col.ash, 0.95);
        else if (m === SMOKE) px(buf, o, col.smoke, 0.8);
        else if (m === FIRE) {
          // 매 틱 fire/flame/gold 랜덤 스왑 — 타오르는 질감
          const r3 = rand();
          const fc = r3 < 0.4 ? col.fire : r3 < 0.8 ? col.flame : col.gold;
          px(buf, o, fc, 0.85 + 0.3 * flicker);
        }
      }
    }
    ctx.putImageData(img, 0, 0);

    // 잔광(안개) — 중심이 sin/cos 로 천천히 도는 radial gradient, 알파 낮게 — 화면이 늘 살아 있다
    const gx = W * (0.5 + 0.3 * Math.sin(t * 0.9));
    const gy = H * (0.55 + 0.26 * Math.cos(t * 0.7));
    const gr = Math.max(W, H) * 0.52;
    const g = ctx.createRadialGradient(gx, gy, 0, gx, gy, gr);
    g.addColorStop(0, `rgba(${col.glow.join(",")},0.07)`);
    g.addColorStop(1, `rgba(${col.glow.join(",")},0)`);
    ctx.fillStyle = g;
    ctx.fillRect(0, 0, W, H);
  }

  function fit(): void {
    const field = fieldRef.current;
    const cv = cvRef.current;
    if (!field || !cv) return;
    const ctx = cv.getContext("2d");
    if (!ctx) return;
    const r = field.getBoundingClientRect();
    sizeRef.current.w = r.width;
    sizeRef.current.h = r.height;
    cv.width = Math.round(r.width);
    cv.height = Math.round(r.height);
    ctxRef.current = ctx;
    dimsRef.current.cols = Math.max(8, Math.floor(r.width / CELL));
    dimsRef.current.rows = Math.max(8, Math.floor(r.height / CELL));
    build();
    scheduleIgnitions();
    tickRef.current = 0;
  }

  function stillFrame(): void {
    // reduce — 점화 직후 몇 틱만 돌리고 한 장
    doIgnite("wood1");
    for (let k = 0; k < 12; k++) update();
    draw(0.2);
  }

  let t0 = -1;
  let prev = 0;
  let acc = 0;
  function frame(now: number): void {
    if (t0 < 0) t0 = now;
    acc += now - (prev || now);
    prev = now;
    while (acc >= STEP) {
      update();
      const t = tickRef.current / 60;
      const igns = ignRef.current;
      while (ignIdxRef.current < igns.length && igns[ignIdxRef.current].at <= t) {
        doIgnite(igns[ignIdxRef.current].kind);
        ignIdxRef.current++;
      }
      acc -= STEP;
    }
    draw((now - t0) / 1000);
    rafRef.current = requestAnimationFrame(frame);
  }

  useEffect(() => {
    const root = rootRef.current;
    if (!root) return;
    ignitePRef.current = igniteP;
    lifeRef.current = life;
    colRef.current = {
      night: tokRGB(root, "--sand-night"),
      glow: tokRGB(root, "--sand-glow"),
      fire: tokRGB(root, "--sand-fire"),
      flame: tokRGB(root, "--sand-flame"),
      gold: tokRGB(root, "--sand-gold"),
      ash: tokRGB(root, "--sand-ash"),
      smoke: tokRGB(root, "--sand-smoke"),
      wood: tokRGB(root, "--sand-wood"),
    };
    randRef.current = makePRNG(0x318a44);
    fit();
    setN(String(Math.round(igniteP * 100)));
    function onResize(): void {
      fit();
      if (reduced()) stillFrame();
    }
    window.addEventListener("resize", onResize);
    if (reduced()) {
      stillFrame();
      setStill(true);
    } else {
      rafRef.current = requestAnimationFrame(frame);
    }
    return () => {
      window.removeEventListener("resize", onResize);
      cancelAnimationFrame(rafRef.current);
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [igniteP, life]);

  const rootCls = still ? `${styles.root} ${styles.isStill}` : styles.root;

  return (
    <main className={styles.stage}>
      <div className={rootCls} ref={rootRef} style={vars}>
        <p className={styles.hint}>
          <span>불은 이웃한 나무를 확률로 태우고, 스스로는 재가 됩니다</span>
        </p>
        <div
          className={styles.field}
          ref={fieldRef}
          role="application"
          aria-label={FIELD_LABEL}
          tabIndex={0}
        >
          <canvas className={styles.cv} ref={cvRef}></canvas>
        </div>
        <div className={styles.bar}>
          <span className={styles.meta}><b className={styles.val}>{n}</b>점화 확률 %</span>
          <span className={styles.metaDim}>canvas · ImageData · requestAnimationFrame</span>
        </div>
      </div>
    </main>
  );
}