estudando vetores em processing.

v.pde

int x, y;

void setup() {
  size(800, 450);
  background(255);
  fill(0, 0, 100, 20);
  strokeWeight(1.8);
  stroke(0, 0, 100, 80);
}

void draw() {
  background(255);
  PVector p = PVector.random2D();
  //p.add(new PVector(width/2, height/2));
  p.add(pos());
  //println(p.toString());
  //println(update().toString());
  ellipse(p.x, p.y, 120, 120);
  line(p.x, p.y, p.x + 120/4, p.y + 120/4);
  PVector m = new PVector((width/2 + 120/4) - p.x, (height/2 + 120/4) - p.y);
  //rect(m.x, m.y, 10, 10);
}

PVector pos() {
  if (mousePressed) {
    return new PVector(random(width), random(height));
  }
  return new PVector(width/2, height/2);
}

PVector random2D() {
  return new PVector(round(random(-1, 0)), round(random(-1, 0)), 0);
}