let xspeed, yspeed; // speed of the ball

let ballSize = 20; // size of the ball

function preload(){

}

function setup() {

  createCanvas(400, 400);

  x = width / 2; // start in the middle of the canvas

  y = height / 2;

  xspeed = random(-5, 5); // random speed in x and y directions

  yspeed = random(-5, 5);

}

​

function draw() {

  background(0); // black background

  fill(255); // white ball

  ellipse(x, y, ballSize, ballSize); // draw the ball

  x += xspeed; // move the ball

  y += yspeed;

  if (x + ballSize / 2 > width || x - ballSize / 2 < 0) { // bounce off walls

    xspeed = -xspeed;

  }

  if (y + ballSize / 2 > height || y - ballSize / 2 < 0) {

    yspeed = -yspeed;

  }

}

​