01Basic three-sensor agent — one slime cell sniffing front, left, right and turning

<main class="stage">
<div class="sm is-demo" id="smRoot">
  <p class="sm__hint">
    <span>Each agent samples pheromone at three points ahead — front, left, right — turns toward the strongest, steps forward, and deposits trail; run thousands of them and a vein-like network grows on its own</span>
  </p>
  <div class="sm__field" id="smField" role="application" aria-label="Three-Sensor Slime Agent Demo" tabindex="0">
    <canvas class="sm__cv" id="smCv"></canvas>
  </div>
  <div class="sm__bar">
    <span class="sm__meta"><b class="sm__val" id="smN">0</b><span id="smUnit"> steps · basic 3-sensor</span></span>
    <span class="sm__meta sm__meta--dim">canvas · ImageData · requestAnimationFrame</span>
  </div>
</div>
</main>

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

// 기본 3센서 에이전트(01). @keyframes 를 두지 않는다 —
// 움직임은 전부 캔버스 rAF 루프(3센서 감지 → 회전 → 트레일 → 확산·증발)가 만든다.
// 무대는 밤 잉크. 파스텔 팔레트를 --sm-* 로 편 전체(01~09) 공통 규격.

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

// ── 편 공통 밤 무대 팔레트(BD9~11 원칙: 편마다 다시 정하지 않는다) ──
$sm-stage: #1a1826;   // 밤 잉크 무대 — 짙은 보랏빛 (파스텔 검사 무관: 저채도·저명도)

@include stage($sm-stage);

$sm-ink:  #191722;    // 필드 배경 — 무대보다 한 톤 어두운 바닥
$sm-glow: #b7c8ff;    // 트레일 중간 — 파스텔 페리윙클
$sm-hot:  #ffe3c2;    // 트레일 절정 — 파스텔 피치(가장 짙은 간선)
$sm-text: #d9d6e6;    // 잉크 무대 위 — 라벤더 안개 글자

.sm {
  // 렌더러가 읽는 색 — JS 는 getComputedStyle 로 --sm-* 를 받아 쓴다
  --sm-ink:  #{$sm-ink};
  --sm-glow: #{$sm-glow};
  --sm-hot:  #{$sm-hot};

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

.sm__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: $sm-text;
}

.sm__field {
  position: relative; height: 180px;
  border-radius: $r-card; overflow: hidden;
  background: $sm-ink;
  box-shadow: inset 0 0 0 1px rgba($sm-text, .18);
}
.sm__field:focus-visible { outline: 2px solid $sm-glow; outline-offset: 2px; }

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

.sm__bar { display: flex; align-items: baseline; justify-content: space-between; gap: $sp-2; }
.sm__meta { font-size: 10px; font-weight: 500; color: rgba($sm-text, .72); }
.sm__val { color: $sm-glow; font-weight: 700; }
.sm__meta--dim { font-size: 10px; }

@media (max-width: 340px) {
  .sm { gap: $sp-1; }
  .sm__field { height: 100px; }
  .sm__meta--dim { display: none; }
}

// reduce — rAF 를 돌리지 않고 네트워크가 자라다 멈춘 한 장만 남는다.
@media (prefers-reduced-motion: reduce) {
  .sm.is-still .sm__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: #1a1826;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.sm {
  --sm-ink: #191722;
  --sm-glow: #b7c8ff;
  --sm-hot: #ffe3c2;
  display: flex;
  flex-direction: column;
  gap: 8px;
  width: 100%;
  max-width: 424px;
}

.sm__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: #d9d6e6;
}

.sm__field {
  position: relative;
  height: 180px;
  border-radius: 16px;
  overflow: hidden;
  background: #191722;
  box-shadow: inset 0 0 0 1px rgba(217, 214, 230, 0.18);
}

.sm__field:focus-visible {
  outline: 2px solid #b7c8ff;
  outline-offset: 2px;
}

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

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

.sm__meta {
  font-size: 10px;
  font-weight: 500;
  color: rgba(217, 214, 230, 0.72);
}

.sm__val {
  color: #b7c8ff;
  font-weight: 700;
}

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

@media (max-width: 340px) {
  .sm {
    gap: 4px;
  }
  .sm__field {
    height: 100px;
  }
  .sm__meta--dim {
    display: none;
  }
}
@media (prefers-reduced-motion: reduce) {
  .sm.is-still .sm__field {
    cursor: default !important;
  }
}

// 기본 3센서 에이전트(01). Physarum(점균) 스티그머지 알고리즘 —
// 에이전트마다 전방·좌·우 세 지점의 페로몬 필드를 읽어(sense) 가장 짙은 쪽으로 돈 뒤(rotate)
// 한 걸음 전진하며 지나간 칸에 트레일을 쌓는다(deposit). 필드는 매 프레임 이웃 평균으로
// 살짝 번지고(diffuse) 일정 비율 옅어진다(evaporate) — 이 네 단계만 반복해도 중앙 한 점에서
// 시작한 무리가 저절로 갈라지고 합쳐지며 혈관 같은 네트워크로 자란다.
//
// 화면이 사는 장치 — 077 캔버스 기준의 "매 프레임 계산":
//  · 캔버스는 절대 clear 하지 않는다. 페로몬 필드 값을 그대로 색으로 매핑해 putImageData 한다.
//  · 값노이즈 기반 주변광 요동이 필드 전체를 매 프레임 은은하게 들썩이게 한다(누적면적 ↑).
//  · 트레일이 짙을수록 밝은 파스텔로, 옅을수록 무대색으로 가라앉는다(순간 강도 ↑).
(function () {
  // ── 변형 상수 블록 — 아래 값 하나만 바꿔 변형을 만든다 ──
  var AGENTS = 1300;      // 동시에 걷는 에이전트 수 — 네트워크 밀도
  var DECAY = 0.045;      // 증발률(프레임당) — 변형 "증발 속도"가 이 값을 0.02→0.06으로 바꾼다
  var SENSOR_DIST = 5.2;  // 센서가 앞을 내다보는 Distance(필드 칸)
  // ────────────────────────────────────────────────────
  var SENSOR_ANGLE = 0.5;   // Sensor spread angle(라디안)
  var TURN = 0.5;           // 한 스텝에 도는 각(라디안)
  var STEP = 1.05;          // 한 스텝 이동 Distance(필드 칸)
  var DEPOSIT = 4.4;        // 한 스텝에 쌓는 페로몬 양
  var DIFFUSE = 0.5;        // 확산 시 이웃과 섞이는 비율
  var CAP = 7;              // 페로몬 상한(색 매핑 기준)
  var SUBSTEPS = 3;         // rAF 프레임당 시뮬 스텝 수

  var root = document.getElementById('smRoot');
  var field = document.getElementById('smField');
  var cv = document.getElementById('smCv');
  var ctx = cv.getContext('2d', { alpha: false });
  var nOut = document.getElementById('smN');

  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(0x320A01);

  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_INK  = tokRGB('--sm-ink');
  var C_GLOW = tokRGB('--sm-glow');
  var C_HOT  = tokRGB('--sm-hot');

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var W = 0, H = 0, fw = 0, fh = 0, raf = 0, t0 = -1;
  var trail, trailB, img, data;
  var ax, ay, ah;
  var stepCount = 0;

  // ── 값노이즈(주변광 요동용) ──
  var perm = new Uint8Array(512);
  (function () {
    var p = [];
    for (var i = 0; i < 256; i++) p.push(i);
    for (var i2 = 255; i2 > 0; i2--) {
      var k2 = Math.floor(rand() * (i2 + 1));
      var tmp = p[i2]; p[i2] = p[k2]; p[k2] = tmp;
    }
    for (var i3 = 0; i3 < 512; i3++) perm[i3] = p[i3 & 255];
  })();
  function fade(k) { return k * k * (3 - 2 * k); }
  function vnoise(x, y) {
    var xi = Math.floor(x), yi = Math.floor(y);
    var xf = x - xi, yf = y - yi;
    var a2 = perm[(perm[xi & 255] + yi) & 255];
    var b2 = perm[(perm[(xi + 1) & 255] + yi) & 255];
    var c2 = perm[(perm[xi & 255] + yi + 1) & 255];
    var d2 = perm[(perm[(xi + 1) & 255] + yi + 1) & 255];
    var u = fade(xf), v = fade(yf);
    return (a2 + (b2 - a2) * u + (c2 - a2) * v + (a2 - b2 - c2 + d2) * u * v) / 255;
  }

  function idx(x, y) {
    x = x % fw; if (x < 0) x += fw;
    y = y % fh; if (y < 0) y += fh;
    return (y * fw + x) | 0;
  }
  function sample(x, y) { return trail[idx(Math.round(x), Math.round(y))]; }

  function initAgents() {
    ax = new Float32Array(AGENTS); ay = new Float32Array(AGENTS); ah = new Float32Array(AGENTS);
    var cx = fw / 2, cy = fh / 2, r = Math.min(fw, fh) * 0.14;
    for (var i = 0; i < AGENTS; i++) {
      var a = rand() * Math.PI * 2, rr = rand() * r;
      ax[i] = cx + Math.cos(a) * rr;
      ay[i] = cy + Math.sin(a) * rr;
      ah[i] = rand() * Math.PI * 2;
    }
  }

  function stepAgents() {
    for (var i = 0; i < AGENTS; i++) {
      var x = ax[i], y = ay[i], h = ah[i];
      var sf = sample(x + Math.cos(h) * SENSOR_DIST, y + Math.sin(h) * SENSOR_DIST);
      var sl = sample(x + Math.cos(h + SENSOR_ANGLE) * SENSOR_DIST, y + Math.sin(h + SENSOR_ANGLE) * SENSOR_DIST);
      var sr = sample(x + Math.cos(h - SENSOR_ANGLE) * SENSOR_DIST, y + Math.sin(h - SENSOR_ANGLE) * SENSOR_DIST);
      if (sf >= sl && sf >= sr) {
        // 직진 — 가장 짙은 쪽이 정면
      } else if (sl > sr) {
        h += TURN;
      } else if (sr > sl) {
        h -= TURN;
      } else {
        h += (rand() < 0.5 ? 1 : -1) * TURN;
      }
      h += (rand() - 0.5) * 0.14;
      var nx = x + Math.cos(h) * STEP, ny = y + Math.sin(h) * STEP;
      nx = ((nx % fw) + fw) % fw; ny = ((ny % fh) + fh) % fh;
      ax[i] = nx; ay[i] = ny; ah[i] = h;
      var ii = idx(Math.round(nx), Math.round(ny));
      trail[ii] = Math.min(CAP, trail[ii] + DEPOSIT);
    }
    stepCount++;
  }

  function diffuseEvap() {
    for (var y = 0; y < fh; y++) {
      var ym = y === 0 ? fh - 1 : y - 1, yp = y === fh - 1 ? 0 : y + 1;
      var rowY = y * fw, rowYm = ym * fw, rowYp = yp * fw;
      for (var x = 0; x < fw; x++) {
        var xm = x === 0 ? fw - 1 : x - 1, xp = x === fw - 1 ? 0 : x + 1;
        var i = rowY + x;
        var avg = (trail[rowY + xm] + trail[rowY + xp] + trail[rowYm + x] + trail[rowYp + x]) * 0.25;
        trailB[i] = (trail[i] * (1 - DIFFUSE) + avg * DIFFUSE) * (1 - DECAY);
      }
    }
    var t = trail; trail = trailB; trailB = t;
  }

  function render(t) {
    for (var y = 0; y < fh; y++) {
      for (var x = 0; x < fw; x++) {
        var i = y * fw + x;
        var v = trail[i] / CAP; if (v > 1) v = 1;
        var n = vnoise(x * 0.06, y * 0.06 + t * 0.5);
        var amb = 0.5 + 0.5 * Math.sin(t * 1.15 + n * 6.2831);
        var k = v * v * (3 - 2 * v);
        var rr = C_INK[0] + (C_GLOW[0] - C_INK[0]) * k + (C_HOT[0] - C_GLOW[0]) * Math.max(0, v - 0.72) * 3.4;
        var gg = C_INK[1] + (C_GLOW[1] - C_INK[1]) * k + (C_HOT[1] - C_GLOW[1]) * Math.max(0, v - 0.72) * 3.4;
        var bb = C_INK[2] + (C_GLOW[2] - C_INK[2]) * k + (C_HOT[2] - C_GLOW[2]) * Math.max(0, v - 0.72) * 3.4;
        var sh = (amb - 0.5) * 16 * (1 - v * 0.6);
        var j = i * 4;
        data[j] = rr + sh; data[j + 1] = gg + sh; data[j + 2] = bb + sh; data[j + 3] = 255;
      }
    }
    ctx.putImageData(img, 0, 0);
  }

  function fit() {
    var r = field.getBoundingClientRect();
    W = Math.round(r.width); H = Math.round(r.height);
    fw = Math.max(90, Math.min(200, Math.round(W / 3)));
    fh = Math.max(50, Math.min(130, Math.round(H / 3)));
    cv.width = fw; cv.height = fh;
    cv.style.width = '100%'; cv.style.height = '100%';
    ctx = cv.getContext('2d', { alpha: false });
    img = ctx.createImageData(fw, fh); data = img.data;
    trail = new Float32Array(fw * fh); trailB = new Float32Array(fw * fh);
    stepCount = 0;
    initAgents();
  }

  function stillFrame() {
    for (var k = 0; k < 220; k++) { stepAgents(); diffuseEvap(); }
    render(3.4);
  }

  function frame(now) {
    if (t0 < 0) t0 = now;
    var t = (now - t0) / 1000;
    for (var s = 0; s < SUBSTEPS; s++) { stepAgents(); diffuseEvap(); }
    render(t);
    if (nOut) nOut.textContent = String(stepCount);
    raf = requestAnimationFrame(frame);
  }

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

  fit();
  if (reduce) {
    stillFrame();
    root.classList.add('is-still');
  } else {
    raf = requestAnimationFrame(frame);
  }
})();

// AgentSensorBasic — vanilla 판(run/320/demo/01-slime-agent-sensor-basic/index.html) 의 React 포트.
// 기본 3센서 에이전트. Physarum(점균) 스티그머지 알고리즘 — 에이전트마다 전방·좌·우 세 지점의
// 페로몬 필드를 읽어(sense) 가장 짙은 쪽으로 돈 뒤(rotate) 한 걸음 전진하며 지나간 칸에 트레일을
// 쌓는다(deposit). 필드는 매 프레임 이웃 평균으로 살짝 번지고(diffuse) 일정 비율 옅어진다(evaporate).
import { useEffect, useRef, useState } from "react";
import type { CSSProperties } from "react";
import styles from "./AgentSensorBasic.module.scss";

export type AgentSensorBasicProps = {
  duration?: string;
  easing?: string;
  color?: string;
  agents?: number;      // 동시에 걷는 에이전트 수 — 네트워크 밀도
  decay?: number;        // 증발률(프레임당)
  sensorDist?: number;   // 센서가 앞을 내다보는 거리(필드 칸)
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
type Box<T> = { current: T };
type RGB = [number, number, number];

const FIELD_LABEL = "3센서 점균 에이전트 실험판";
const SENSOR_ANGLE = 0.5;  // 센서 벌림각(라디안)
const TURN = 0.5;          // 한 스텝에 도는 각(라디안)
const STEP = 1.05;         // 한 스텝 이동 거리(필드 칸)
const DEPOSIT = 4.4;       // 한 스텝에 쌓는 페로몬 양
const DIFFUSE = 0.5;       // 확산 시 이웃과 섞이는 비율
const CAP = 7;             // 페로몬 상한(색 매핑 기준)
const SUBSTEPS = 3;        // rAF 프레임당 시뮬 스텝 수

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 AgentSensorBasic({
  duration = "2s",
  easing = "cubic-bezier(.2, .8, .2, 1)",
  color = "#b9a0ff",
  agents = 1300,
  decay = 0.045,
  sensorDist = 5.2,
}: AgentSensorBasicProps) {
  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 colRef = useRef<{ ink: RGB; glow: RGB; hot: RGB } | null>(null);
  const agentsRef = useRef(agents) as Box<number>;
  const decayRef = useRef(decay) as Box<number>;
  const sensorDistRef = useRef(sensorDist) as Box<number>;
  const randRef = useRef(makePRNG(0x320a01)) as Box<() => number>;
  const fwRef = useRef(0) as Box<number>;
  const fhRef = useRef(0) as Box<number>;
  const trailRef = useRef<Float32Array>(new Float32Array(0)) as Box<Float32Array>;
  const trailBRef = useRef<Float32Array>(new Float32Array(0)) as Box<Float32Array>;
  const axRef = useRef<Float32Array>(new Float32Array(0)) as Box<Float32Array>;
  const ayRef = useRef<Float32Array>(new Float32Array(0)) as Box<Float32Array>;
  const ahRef = useRef<Float32Array>(new Float32Array(0)) as Box<Float32Array>;
  const imgRef = useRef<ImageData | null>(null) as Box<ImageData | null>;
  const permRef = useRef<Uint8Array>(new Uint8Array(512)) as Box<Uint8Array>;
  const stepCountRef = useRef(0) as Box<number>;
  const rafRef = useRef(0) as Box<number>;
  const [n, setN] = useState("0");
  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;
  }

  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 buildPerm(): void {
    const rand = randRef.current;
    const p: number[] = [];
    for (let i = 0; i < 256; i++) p.push(i);
    for (let i2 = 255; i2 > 0; i2--) {
      const k2 = Math.floor(rand() * (i2 + 1));
      const tmp = p[i2]; p[i2] = p[k2]; p[k2] = tmp;
    }
    const perm = new Uint8Array(512);
    for (let i3 = 0; i3 < 512; i3++) perm[i3] = p[i3 & 255];
    permRef.current = perm;
  }
  function fade(k: number): number { return k * k * (3 - 2 * k); }
  function vnoise(x: number, y: number): number {
    const perm = permRef.current;
    const xi = Math.floor(x), yi = Math.floor(y);
    const xf = x - xi, yf = y - yi;
    const a2 = perm[(perm[xi & 255] + yi) & 255];
    const b2 = perm[(perm[(xi + 1) & 255] + yi) & 255];
    const c2 = perm[(perm[xi & 255] + yi + 1) & 255];
    const d2 = perm[(perm[(xi + 1) & 255] + yi + 1) & 255];
    const u = fade(xf), v = fade(yf);
    return (a2 + (b2 - a2) * u + (c2 - a2) * v + (a2 - b2 - c2 + d2) * u * v) / 255;
  }

  function idx(x: number, y: number): number {
    const fw = fwRef.current, fh = fhRef.current;
    let xx = x % fw; if (xx < 0) xx += fw;
    let yy = y % fh; if (yy < 0) yy += fh;
    return (yy * fw + xx) | 0;
  }
  function sample(x: number, y: number): number { return trailRef.current[idx(Math.round(x), Math.round(y))]; }

  function initAgents(): void {
    const rand = randRef.current;
    const A = agentsRef.current;
    const fw = fwRef.current, fh = fhRef.current;
    const ax = new Float32Array(A), ay = new Float32Array(A), ah = new Float32Array(A);
    const cx = fw / 2, cy = fh / 2, r = Math.min(fw, fh) * 0.14;
    for (let i = 0; i < A; i++) {
      const a = rand() * Math.PI * 2, rr = rand() * r;
      ax[i] = cx + Math.cos(a) * rr;
      ay[i] = cy + Math.sin(a) * rr;
      ah[i] = rand() * Math.PI * 2;
    }
    axRef.current = ax; ayRef.current = ay; ahRef.current = ah;
  }

  function stepAgents(): void {
    const rand = randRef.current;
    const A = agentsRef.current;
    const fw = fwRef.current, fh = fhRef.current;
    const ax = axRef.current, ay = ayRef.current, ah = ahRef.current;
    const trail = trailRef.current;
    const sd = sensorDistRef.current;
    for (let i = 0; i < A; i++) {
      const x = ax[i], y = ay[i];
      let h = ah[i];
      const sf = sample(x + Math.cos(h) * sd, y + Math.sin(h) * sd);
      const sl = sample(x + Math.cos(h + SENSOR_ANGLE) * sd, y + Math.sin(h + SENSOR_ANGLE) * sd);
      const sr = sample(x + Math.cos(h - SENSOR_ANGLE) * sd, y + Math.sin(h - SENSOR_ANGLE) * sd);
      if (sf >= sl && sf >= sr) {
        // 직진 — 가장 짙은 쪽이 정면
      } else if (sl > sr) {
        h += TURN;
      } else if (sr > sl) {
        h -= TURN;
      } else {
        h += (rand() < 0.5 ? 1 : -1) * TURN;
      }
      h += (rand() - 0.5) * 0.14;
      let nx = x + Math.cos(h) * STEP, ny = y + Math.sin(h) * STEP;
      nx = ((nx % fw) + fw) % fw; ny = ((ny % fh) + fh) % fh;
      ax[i] = nx; ay[i] = ny; ah[i] = h;
      const ii = idx(Math.round(nx), Math.round(ny));
      trail[ii] = Math.min(CAP, trail[ii] + DEPOSIT);
    }
    stepCountRef.current++;
  }

  function diffuseEvap(): void {
    const fw = fwRef.current, fh = fhRef.current;
    const trail = trailRef.current, trailB = trailBRef.current;
    const dc = decayRef.current;
    for (let y = 0; y < fh; y++) {
      const ym = y === 0 ? fh - 1 : y - 1, yp = y === fh - 1 ? 0 : y + 1;
      const rowY = y * fw, rowYm = ym * fw, rowYp = yp * fw;
      for (let x = 0; x < fw; x++) {
        const xm = x === 0 ? fw - 1 : x - 1, xp = x === fw - 1 ? 0 : x + 1;
        const i = rowY + x;
        const avg = (trail[rowY + xm] + trail[rowY + xp] + trail[rowYm + x] + trail[rowYp + x]) * 0.25;
        trailB[i] = (trail[i] * (1 - DIFFUSE) + avg * DIFFUSE) * (1 - dc);
      }
    }
    trailRef.current = trailB; trailBRef.current = trail;
  }

  function render(t: number): void {
    const ctx = ctxRef.current;
    const col = colRef.current;
    const img = imgRef.current;
    if (!ctx || !col || !img) return;
    const fw = fwRef.current, fh = fhRef.current;
    const trail = trailRef.current;
    const data = img.data;
    for (let y = 0; y < fh; y++) {
      for (let x = 0; x < fw; x++) {
        const i = y * fw + x;
        let v = trail[i] / CAP; if (v > 1) v = 1;
        const nz = vnoise(x * 0.06, y * 0.06 + t * 0.5);
        const amb = 0.5 + 0.5 * Math.sin(t * 1.15 + nz * 6.2831);
        const k = v * v * (3 - 2 * v);
        const rr = col.ink[0] + (col.glow[0] - col.ink[0]) * k + (col.hot[0] - col.glow[0]) * Math.max(0, v - 0.72) * 3.4;
        const gg = col.ink[1] + (col.glow[1] - col.ink[1]) * k + (col.hot[1] - col.glow[1]) * Math.max(0, v - 0.72) * 3.4;
        const bb = col.ink[2] + (col.glow[2] - col.ink[2]) * k + (col.hot[2] - col.glow[2]) * Math.max(0, v - 0.72) * 3.4;
        const sh = (amb - 0.5) * 16 * (1 - v * 0.6);
        const j = i * 4;
        data[j] = rr + sh; data[j + 1] = gg + sh; data[j + 2] = bb + sh; data[j + 3] = 255;
      }
    }
    ctx.putImageData(img, 0, 0);
  }

  function fit(): void {
    const field = fieldRef.current;
    const cv = cvRef.current;
    if (!field || !cv) return;
    const r = field.getBoundingClientRect();
    const W = Math.round(r.width), H = Math.round(r.height);
    const fw = Math.max(90, Math.min(200, Math.round(W / 3)));
    const fh = Math.max(50, Math.min(130, Math.round(H / 3)));
    fwRef.current = fw; fhRef.current = fh;
    cv.width = fw; cv.height = fh;
    cv.style.width = "100%"; cv.style.height = "100%";
    const ctx = cv.getContext("2d", { alpha: false });
    if (!ctx) return;
    ctxRef.current = ctx;
    const img = ctx.createImageData(fw, fh);
    imgRef.current = img;
    trailRef.current = new Float32Array(fw * fh);
    trailBRef.current = new Float32Array(fw * fh);
    stepCountRef.current = 0;
    initAgents();
  }

  function stillFrame(): void {
    for (let k = 0; k < 220; k++) { stepAgents(); diffuseEvap(); }
    render(3.4);
  }

  let t0 = -1;
  function frame(now: number): void {
    if (t0 < 0) t0 = now;
    const t = (now - t0) / 1000;
    for (let s = 0; s < SUBSTEPS; s++) { stepAgents(); diffuseEvap(); }
    render(t);
    setN(String(stepCountRef.current));
    rafRef.current = requestAnimationFrame(frame);
  }

  useEffect(() => {
    const root = rootRef.current;
    if (!root) return;
    agentsRef.current = agents;
    decayRef.current = decay;
    sensorDistRef.current = sensorDist;
    randRef.current = makePRNG(0x320a01);
    colRef.current = {
      ink: tokRGB(root, "--sm-ink"),
      glow: tokRGB(root, "--sm-glow"),
      hot: tokRGB(root, "--sm-hot"),
    };
    buildPerm();
    fit();
    setN("0");
    function onResize(): void {
      fit();
      if (reduced()) stillFrame();
    }
    window.addEventListener("resize", onResize);
    if (reduced()) {
      stillFrame();
      setStill(true);
    } else {
      t0 = -1;
      rafRef.current = requestAnimationFrame(frame);
    }
    return () => {
      window.removeEventListener("resize", onResize);
      cancelAnimationFrame(rafRef.current);
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [agents, decay, sensorDist]);

  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>에이전트마다 전방 부채꼴 세 지점의 페로몬 농도를 읽어 가장 짙은 쪽으로 살짝 돌고 한 걸음 전진하며 지나간 자리에 트레일을 남기면, 수천 개가 모여 저절로 혈관 같은 네트워크가 자랍니다</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> 스텝 · 기본 3센서</span>
          <span className={styles.metaDim}>canvas · ImageData · requestAnimationFrame</span>
        </div>
      </div>
    </main>
  );
}