let nextGrid;

let dA = 2.9;

let dB = 1.5;

let feed = 0.096;

let kill = 0.862;

​

function setup() {

  createCanvas(400, 400);

  pixelDensity(1);

  grid = [];

  nextGrid = [];

  for (let x = 0; x < width; x++) {

    grid[x] = [];

    nextGrid[x] = [];

    for (let y = 0; y < height; y++) {

      grid[x][y] = {

        a:0.5,

        b: noise(x * 0.2, y * 0.1) > 0.2 ? 0 : 4  // initialize using Perlin noise

      };

      nextGrid[x][y] = {a: 1, b: 0};

    }

  }

}

​

function draw() {

  background(220);

​

  for (let x = 1; x < width - 1; x++) {

    for (let y = 1; y < height - 1; y++) {

      let a = grid[x][y].a;

      let b = grid[x][y].b;

      nextGrid[x][y].a = a +

          (dA * laplaceA(x, y)) -

          (a * b * b) +

          (feed * (1 - a));

      nextGrid[x][y].b = b +

          (dB * laplaceB(x, y)) +

          (a * b * b) -

          ((kill + feed) * b);

      nextGrid[x][y].a = constrain(nextGrid[x][y].a, 0, 1);

      nextGrid[x][y].b = constrain(nextGrid[x][y].b, 0, 1);

    }

  }

  loadPixels();

  for (let x = 0; x < width; x++) {

    for (let y = 0; y < height; y++) {

      let pix = (x + y * width) * 4;

      let a = nextGrid[x][y].a;

      let b = nextGrid[x][y].b;

      let c = floor((a - b) * 255);

      let n = noise(x * 0.1, y * 0.1) * 25; // Perlin noise influence

      pixels[pix + 0] = n + c % 255;

      pixels[pix + 1] = n;

      pixels[pix + 2] = c;

      pixels[pix + 3] = 255;

    }

  }

  updatePixels();

  swap();

}

​

function swap() {

  let temp = grid;

  grid = nextGrid;

  nextGrid = temp;

}

​

function laplaceA(x, y) {

  let sumA = 0;

  sumA += grid[x][y].a * -1;

  sumA += grid[x - 1][y].a * 0.2;

  sumA += grid[x + 1][y].a * 0.2;

  sumA += grid[x][y - 1].a * 0.2;

  sumA += grid[x][y + 1].a * 0.5;

  sumA += grid[x - 1][y - 1].a * 0.05;

  sumA += grid[x + 1][y - 1].a * 0.09;

  sumA += grid[x + 1][y + 1].a * 0.05;

  sumA += grid[x - 1][y + 1].a * 0.05;

  return sumA;

}

​

function laplaceB(x, y) {

  let sumB = 0;

  sumB += grid[x][y].b * -1;

  sumB += grid[x - 1][y].b * 0.2;

  sumB += grid[x + 1][y].b * 0.4;

  sumB += grid[x][y - 1].b * 0.7;

  sumB += grid[x][y + 1].b * 0.2;

  sumB += grid[x - 1][y - 1].b * 0.05;

  sumB += grid[x + 1][y - 1].b * 0.05;

  sumB += grid[x + 1][y + 1].b * 0.05;

  sumB += grid[x - 1][y + 1].b * 0.05;

  return sumB;

}

​