let d = 150;

let loc;

let vel;

let sph = d/2;

​

function setup() {

  createCanvas(600, 600, WEBGL);

  loc = createVector(0, 0, 0);

  vel = createVector(random(1, 3), random(1, 3), random(1, 3));

}

​

function draw() {

  background(220);

  loc.add(vel);

  noFill()

  rotateY(PI/4.0)

  box(2*d);

  push()

  stroke(5);

  fill(255, 0, 0);

  translate(loc.x, loc.y, loc.z);

  if (loc.x > d - sph || loc.x < -d + sph) {

    vel.x *= -1;

  }

  if (loc.y > d - sph || loc.y < -d + sph) vel.y *= -1;

  if (loc.z > d - sph || loc.z < -d + sph) vel.z *= -1;

  sphere(sph);

  pop();

  /*

  */

}