​

function setup() {

  createCanvas(600, 600);

}

​

  var x = 100;

  var y = 300;

  var s = 20;

  var dx = 5;

  var dy = 5;

​

function draw() {

  background("#003D14");

  fill(255);

  noStroke();

​

  x = x+dx;

  y = y+dy;

  if(x <= s || x >= width-s){

    dx = -dx;

  }

  if(y <= s || y >= height-s){

    dy = -dy;

  }

  ellipse(x,y,s,s);

​

}