let x1, x2;

// Speed of left and right dividers

let xspeed1, xspeed2;

​

// Range of randomly generated xspeeds

let range = 5;

​

// Range of alpha

let low = 0;

let high = 255;

​

// Alpha value

let a = low;

// Fade-in speed

let aspeed = 0.5;

​

// Background color

let bg = high;

​

// Margin

let m = 120;

​

function setup() {

  createCanvas(windowWidth, windowHeight);

  noStroke();

  noCursor();

  randomSeed(0);

  reset();

}

​

function reset() {

  console.log("RESET");

  a = low;

  x1 = width * random(0.1, 0.5);

  x2 = width - x1;

  xspeed1 = random(-range, range); //random(1) > 0.5 ? -range : range;

  // Go the opposite way

  xspeed2 = random(-range, range); //xspeed1 > 0 ? -range : range;

}

​

function draw() {

  background(bg);

  // Is the background white or black?

  // Make it the oppposite color

  fill(bg > low ? low : high, a);

  rect(0, 0, x1, height);

  rect(x2, 0, width - x2, height);

  a += aspeed;

  // If fully faded in

  if (a > high + m || a < low - m) {

    x1 += xspeed1;

    x2 += xspeed2;

    if ((x1 > width || x1 < 0) && (x2 > width || x2 < 0)) {

      if (x1 > width || x2 < 0) {

        // If the background was white, make it black

        bg = bg > low ? low : high;

        console.log(bg);

      }

      reset();

    }

  }

​

//background(0);

​

}