squareSide,

  grid,

  generateButton;

​

function setup() {

  gridSize = 21;

  squareSide = 20;

  grid = [];

  generateButton = createButton("Generate");

  generateButton.mousePressed(generateMaze);

  createCanvas(gridSize * squareSide, gridSize * squareSide);

  baseGrid();

}

​

function draw() {

  noStroke();

  browseGrid(function(x, y, cell) {

    fill(getColor(cell.toString()));

    square(x * squareSide, y * squareSide, squareSide);

  });

}

​

function baseGrid() {

  let cell;

  for (let x = 0; x < gridSize; x++) {

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

      if (x % 2) {

        if (y % 2)

          cell = 0;

        else

          cell = -1;

      } else

        cell = -1;

      grid.push(cell);

    }

  }

}

​

function generateMaze() {

  let wallsCells = [],

      attributedNumber = 0;

  browseGrid(function(x, y, cell) {

    if (cell == -1)

      wallsCells.push(x * gridSize + y);

    else {

      attributedNumber++;

      grid[x * gridSize + y] = attributedNumber;

    }

  });

}

​

function browseGrid(callback) {

  for (let x = 0; x < gridSize; x++) {

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

      callback(x, y, grid[x * gridSize + y]);

    }

  }

}

​

function getColor(number) {

  if (number > 0)

    return color(number % 256, (20 * number + 100) % 256, (30 * number - 200) % 256);

  if (number == 0)

    return color(255);

  return color(0);

}