float vit=1;
int taille =50;
PVector[] squares;

void setup() {
  size(600, 600);

  squares = new PVector[] {
    new PVector(0,0),
    new PVector(taille,taille),
    new PVector(width,0),
    new PVector(width+taille, taille)
  };
}

void draw() {
  background(0);
  for (PVector s : squares) {
    rect(s.x - width, s.y, taille, taille);
    s.x = (s.x + vit) % (width*2);
  }
}