Ant Colony Highways

let W, H, COLS, ROWS, CELL;
let cells;
let img, imgData, pixels;
let buf, bufCtx;
let ants;
let stepsPerFrame = 6000;
let resetTimer = 0;

const ANT_COLORS = [
  [255, 80, 80],
  [80, 200, 255],
  [120, 255, 120],
  [255, 220, 80],
  [220, 120, 255],
];
const RULES = ["RL", "RL", "RL", "RLLR", "RL"];
const OFF_BG = [16, 14, 22];
const ON_BG  = [42, 38, 56];
// Heading -> (dx, dy). Hoisted to module scope so stepAnts doesn't
// reallocate them every frame (it gets called once per frame with ~6000
// inner iterations; the arrays themselves never change).
const DX = [0, 1, 0, -1];
const DY = [-1, 0, 1, 0];

function init({ canvas, ctx, width, height }) {
  W = width; H = height;
  CELL = 3;
  COLS = Math.floor(W / CELL);
  ROWS = Math.floor(H / CELL);
  cells = new Uint8Array(COLS * ROWS);
  img = ctx.createImageData(COLS, ROWS);
  imgData = img;
  pixels = img.data;
  for (let i = 3; i < pixels.length; i += 4) pixels[i] = 255;
  buf = new OffscreenCanvas(COLS, ROWS);
  bufCtx = buf.getContext('2d');
  spawnAnts();
  paintAll();
}

function spawnAnts() {
  cells.fill(0);
  ants = [];
  const n = 4;
  const cx = COLS >> 1, cy = ROWS >> 1;
  const r = Math.min(COLS, ROWS) * 0.18;
  for (let i = 0; i < n; i++) {
    const a = (i / n) * Math.PI * 2;
    ants.push({
      x: Math.round(cx + Math.cos(a) * r),
      y: Math.round(cy + Math.sin(a) * r),
      dir: i & 3,
      id: i,
      rule: RULES[i],
    });
  }
}

function paintAll() {
  for (let i = 0; i < cells.length; i++) writePixel(i, cells[i]);
}

function writePixel(idx, v) {
  const on = v & 1;
  const aid = (v >> 1) & 7;
  let r, g, b;
  if (aid === 0) {
    if (on) { r = ON_BG[0]; g = ON_BG[1]; b = ON_BG[2]; }
    else    { r = OFF_BG[0]; g = OFF_BG[1]; b = OFF_BG[2]; }
  } else {
    const c = ANT_COLORS[aid - 1];
    if (on) { r = c[0]; g = c[1]; b = c[2]; }
    else    { r = (c[0] * 0.32) | 0; g = (c[1] * 0.32) | 0; b = (c[2] * 0.32) | 0; }
  }
  const p = idx * 4;
  pixels[p] = r; pixels[p + 1] = g; pixels[p + 2] = b;
}

function blitScaled(ctx) {
  bufCtx.putImageData(imgData, 0, 0);
  ctx.imageSmoothingEnabled = false;
  ctx.drawImage(buf, 0, 0, COLS, ROWS, 0, 0, W, H);
}

function stepAnts(steps) {
  let alive = 0;
  for (let s = 0; s < steps; s++) {
    alive = 0;
    for (let i = 0; i < ants.length; i++) {
      const a = ants[i];
      if (a.x < 0 || a.x >= COLS || a.y < 0 || a.y >= ROWS) continue;
      alive++;
      const idx = a.y * COLS + a.x;
      const cur = cells[idx];
      const state = cur & 1;
      const turn = a.rule.charCodeAt(state % a.rule.length);
      if (turn === 82) a.dir = (a.dir + 1) & 3;
      else a.dir = (a.dir + 3) & 3;
      const flipped = state ^ 1;
      const newVal = flipped | ((a.id + 1) << 1);
      cells[idx] = newVal;
      writePixel(idx, newVal);
      a.x += DX[a.dir];
      a.y += DY[a.dir];
    }
    if (alive === 0) { resetTimer = 1.2; return; }
  }
}

function tick({ ctx, dt }) {
  if (resetTimer > 0) {
    resetTimer -= dt;
    if (resetTimer <= 0) { spawnAnts(); paintAll(); }
    blitScaled(ctx);
    return;
  }
  stepAnts(stepsPerFrame);
  blitScaled(ctx);
}