var w = 40;

var grid = [];

​

var current;

​

function setup() {

  createCanvas(400, 400);

  cols = floor(width / w);

  rows = floor(height / w);

  frameRate(5);

  for (var j = 0; j < rows; j++) {

    for (var i = 0; i < cols; i++) {

      var cell = new Cell(i, j);

      grid.push(cell);

    }

  }

  current = grid[0];

}

​

function draw() {

  background(51);

  for (var i = 0; i < grid.length; i++) {

    grid[i].show();

  }

  current.visited = true;

  var next = current.checkNeighbours();

  if (next) {

    next.visited = true;

    current = next;

  }

}

​

function index(i, j) {

  if (i < 0 || j < 0 || i > cols - 1 || j > rows - 1) {

    return -1;

  }

  return i + j * cols;

}

​

function Cell(i, j) {

  this.i = i;

  this.j = j;

  this.walls = [true, true, true, true];

  this.checkNeighbours = function() {

    var neighbours = [];

    var top    = grid[index(i, j - 1)];

    var right  = grid[index(i + 1, j)]; 

    var bottom = grid[index(i, j + 1)];

    var left   = grid[index(i - 1, j)];

    if  (top && !top.visited) {

      neighbours.push(top);

    }

    if  (right && !right.visited) {

      neighbours.push(right);

    }

    if  (bottom && !bottom.visited) {

      neighbours.push(bottom);

    }

    if  (left && !left.visited) {

      neighbours.push(left);

    }

    if (neighbours.length > 0) {

      var r = floor(random(0, neighbours.length));

      return neighbours[r];

    } else {

      return undefined;

    }

  };

  this.show = function() {

    var x = this.i * w;

    var y = this.j * w;

    stroke(255);

    if (this.walls[0]) {

      line(x,     y,     x + w, y    );

    }

    if (this.walls[1]) {

      line(x + w, y,     x + w, y + w);

    }

    if (this.walls[2]) {

      line(x + w, y + w, x,     y + w);

    }

    if (this.walls[3]) {

      line(x,     y + w, x,     y    );

    }

    if (this.visited){

      fill(255, 0, 255, 100);

      rect(x, y, w, w);

    }

  };

}