var rad = 130;
var xpos, ypos;

var xspeed = 120;
var yspeed = 332;

var xdirection = 1;
var ydirection = 1;

function setup() {
  createCanvas(windowWidth,
               windowHeight);
  noStroke();
  ellipseMode(RADIUS);

  xpos = width / 3;
  ypos = height / 2;
}

function draw() {
  background(11, 21, 3);
  fill(223, 204, 501);

  xpos = xpos + xspeed * xdirection;
  ypos = ypos + yspeed * ydirection;

  if (xpos > width - rad || xpos < rad) {
    xdirection *= -1;
  }

  if (ypos > height - rad || ypos < rad) {
    ydirection *= -1;
  }

  ellipse(xpos, ypos, rad, rad);
}