var _height = 400;

var counter = _height;

function setup() {

  createCanvas(_width, _height);

}

​

function draw() {

  // background(0);

  counter--;

  noStroke()

  var heightRando = Math.round(random(0,counter));

  for (var i = 0; i < _width; i++) {

    var chance = Math.round(random(0, 1));

    if (chance == 1) fill(0);

    else fill(255);

    rect(i, 0, 1, heightRando);

  }

}

​