let v;

​

let r = 25;

​

function setup() {

  createCanvas(560, 400);

  p = createVector(width / 2, height / 2);

  v = createVector(0, 0);

}

​

function draw() {

  background(255);

  if (keyIsDown(LEFT_ARROW)) {

    v.x = -2;

  }

  if (keyIsDown(RIGHT_ARROW)) {

    v.x = 2;

  }

  if (keyIsDown(UP_ARROW)) {

    v.y = -2;

  }

  if (keyIsDown(DOWN_ARROW)) {

    v.y = 2;

  }

  p.add(v);

  v.mult(0);

  if (p.x > width + r) {

    p.x = -r;

  } else if (p.x < -r) {

    p.x = width + r;

  } else if (p.y > height + r) {

    p.y = -r;

  } else if (p.y < -r) {

    p.y = height + r;

  }

  stroke(0);

  strokeWeight(3);

  fill(200);

  ellipseMode(CENTER);

  ellipse(p.x, p.y, r * 2, r * 2);

}