// Daniel Shiffman

// http://natureofcode.com

​

let w = 8;

let columns, rows;

let board;

​

function setup() {

  createCanvas(640, 240);

  columns = width / w;

  rows = height / w;

  board = create2DArray(columns, rows);

  for (let i = 1; i < columns - 1; i++) {

    for (let j = 1; j < rows - 1; j++) {

      board[i][j] = floor(random(2));

    }

  }

}

​

function draw() {

  // The next board

  let next = create2DArray(columns, rows);

​

  //{!2} Looping but skipping the edge cells

  for (let i = 1; i < columns - 1; i++) {

    for (let j = 1; j < rows - 1; j++) {

      // Add up all the neighbor states to

      // calculate the number of live neighbors.

      let neighborSum = 0;

      for (let k = -1; k <= 1; k++) {

        for (let l = -1; l <= 1; l++) {

          neighborSum += board[i + k][j + l];

        }

      }

      // Correct by subtracting the cell state itself.

      neighborSum -= board[i][j];

​

      //{!4} The rules of life!

      if (board[i][j] == 1 && neighborSum < 2) next[i][j] = 0;

      else if (board[i][j] == 1 && neighborSum > 3) next[i][j] = 0;

      else if (board[i][j] == 0 && neighborSum == 3) next[i][j] = 1;

      else next[i][j] = board[i][j];

    }

  }

​

  for (let i = 0; i < columns; i++) {

    for (let j = 0; j < rows; j++) {

      //{!1} evaluates to 255 when state is 0 and 0 when state is 1

      fill(255 - board[i][j] * 255);

      stroke(0);

      square(i * w, j * w, w);

    }

  }

​

  board = next;

}

​

function create2DArray(columns, rows) {

  let arr = new Array(columns);

  for (let i = 0; i < columns; i++) {

    arr[i] = new Array(rows);

    for (let j = 0; j < rows; j++) {

      arr[i][j] = 0;

    }

  }

  return arr;

}