const h = w;

​

var x, y;

var prevrand;

​

function setup() {

  createCanvas(400, 400);

  background(20);

  ellipseMode(CENTER);

  stroke(220);

  strokeWeight(3);

  noFill();

  y = h/2;

  let rand = parseInt(random(2));

  if(rand == 0) {

    x = 0;

    arc(x, y, w, h, -HALF_PI, HALF_PI);

  }

  else {

    x = w/2;

    arc(x, y, w, h, HALF_PI, -HALF_PI);

  }

  console.log(x);

  prevrand = rand;

}

​

function draw() {

  let rand = parseInt(random(2));

  x += (rand - prevrand + 1) * w/2;

  if(x > width) {

    x = 0;

    y += h;

  }

  if(rand == 0) {

    arc(x, y, w, h, -HALF_PI, HALF_PI);

  }

  else {

    arc(x, y, w, h, HALF_PI, -HALF_PI);

  }

  prevrand = rand;

  // arc(50, 50, 100, 100, HALF_PI, -HALF_PI);

}