var py=300;

  var diameter = 50;

  var vx = 3;

  var vy = 1;

​

function setup() {

  createCanvas(400, 400);

​

}

​

function draw() {

  background(100,100,255,10);

  strokeWeight(0);

  px = px + vx;

  py = py + vy;

  ellipse(px, py, 50, 50);

  var radius = diameter / 2;

  if (px > (width - radius)) {

    vx = 0-vx;

  }

  if (py > (height - radius)) {

    vy = 0-vy;

  }

  if (px < radius) {

    vx = 0-vx;

  }

  if (py < radius) {

    vy = 0-vy;

  }

​

​

​

}