evolve symmetrical art

symm.js

const fs = require('fs');
const PNG = require('pngjs').PNG;

W = 256;
H = 256;
AB = '0123456789';
PSIZE = 128;
GENS = 300;

function choice (arr) {
  return arr[Math.floor(Math.random()*arr.length)];
}

function shuffle (array) {
  let cur = array.length;

  while (cur > 0) {
    const r = Math.floor(Math.random() * cur);
    cur -= 1;

    const temp = array[cur];
    array[cur] = array[r];
    array[r] = temp;
  }

  return array;
};

function randomIndiv (width, height, alphabet) {
  const out = [];
  for (let i = 0; i < height; i++) {
    const row = [];
    for (let j = 0; j < width; j++) {
      row.push(choice(alphabet))
    }
    out.push(row);
  }

  return out;
}

function printIndiv (indiv) {
  let str = "";
  for (let i = 0; i < indiv.length; i++) {
    for (let j = 0; j < indiv[i].length; j++) {
      str += indiv[i][j];
    }
    str += "\n";
  }

  console.log(str);
}

function imgfrom (best, i) {
  const img = new PNG({width:W,height:H});

  for (let y = 0; y < img.height; y++) {
    for (let x = 0; x < img.width; x++) {
      const idx = (img.width * y + x) << 2;
      const col = best[y][x];

      img.data[idx] = Math.floor(256/col);
      img.data[idx + 1] = Math.floor(256/col);
      img.data[idx + 2] = Math.floor(256/col);
      img.data[idx + 3] = 0xFF;
    }
  }

  const buf = PNG.sync.write(img);
  fs.writeFileSync(__dirname + '/out/' + i + '.png', buf);
}

function fitness (indiv) {
  let fitness = 0;
  for (let i = 0; i < indiv.length; i++) {
    for (let j = 0; j < indiv[i].length; j++) {
      const h = indiv.length-1;
      const w = indiv[j].length-1;

      // if (indiv[i][j] == indiv[h-i][j]) { fitness += 1; }
      // if (indiv[i][j] == indiv[i][w-j]) { fitness += 1; }
      // if (indiv[i][j] == indiv[h-i][w-j]) { fitness += 1; }
      fitness += 10 - Math.abs(indiv[i][j] - indiv[h-i][j]);
      fitness += 10 - Math.abs(indiv[i][j] - indiv[i][w-j]);
      fitness += 10 - Math.abs(indiv[i][j] - indiv[h-i][w-j]);
    }
  }

  return fitness;
}

function crossover (indiv1, indiv2) {
  let child = [];
  for (let i = 0; i < indiv1.length; i++) {
    let row = [];
    for (let j = 0; j < indiv1[i].length; j++) {
      if (Math.random() < 0.5) {
        row.push(indiv1[i][j]);
      } else {
        row.push(indiv2[i][j]);
      }
    }
    child.push(row);
  }

  return child;
}

pop = [];
for (let i = 0; i < PSIZE; i++) {
  pop.push(randomIndiv(W, H, AB));
}
pop.sort((b, a) => (fitness(a) - fitness(b)));

best = null;

for (let i = 0; i < GENS; i++) {
  new_p = pop.slice(0, PSIZE/2);

  shuffle(new_p);
  for (let j = 0; j < PSIZE/2; j+=2) {
    new_p.push(crossover(new_p[j], new_p[j+1]));
  }

  while (new_p.length < PSIZE) {
    new_p.push(randomIndiv(W, H, AB));
  }

  pop = new_p;

  pop.sort((b, a) => (fitness(a) - fitness(b)));
  best = pop[0]
  console.log(i, fitness(pop[0]));
  imgfrom(best, i);
}