var y = 200;

var changeY = 3;

var changeX = 3;

var AIx = 500;

var changeD   = -5;

var person = 100;

var D = 200;

​

function setup() {

  createCanvas(600, 400);

}

​

function draw() {

  background(0);

  stroke(255);

  fill(255);

  ellipse(x,y,15,15);

   if (x <= person+5||x==person){

    changeX = changeX*-1;

}

   if (y <= D||y==D){

    changeY = changeY*-1;

}

  x = x + changeX; 

  y = y + changeY;

  if (y > 400){

    changeY = -changeY;

}

    if (y < 0){

    changeY = 3;

}

    if (x > 600){

    changeX = -changeX;

}

    if (x < 0){

    changeX = 3;

}

  rect(AIx,y-30,15,75);

  rect (person, D, 15, 75);

  if (x > 493){

      changeX = -changeX;

}

  if (keyIsDown(UP_ARROW)) {

  D = D + changeD;

      if (D < 0) {

  D = 0;

}

}

   if (keyIsDown(DOWN_ARROW)) {

  D = D - changeD;

      if (D > 325) {

  D = 325;

}

}

​

}