PVector pv;
float rotation;

void setup() {
  size(300, 300);
  rotation = 0.1;
  pv = new PVector(rotation, 0);
  background(255);
}

void draw() {
  translate(width/2.0, height/2.0);
  pv.setMag(pv.mag()+rotation);
  println(pv.mag());
  pv.rotate(rotation/PI);
  point(pv.x, pv.y);
  // check restart
  if (pv.mag()>width/2.0) frameCount=-1;
}