// TODO: optimize
static L<Rect> dropOverlappingRects(L<Rect> l) {
  new L<Rect> out;
  bigloop: for (int i = 0; i < l(l); i++) {
    Rect a = l.get(i);
    for (Rect r : out)
      if (rectsOverlap(a, r))
        continue bigloop;
    out.add(a);
  }
  ret out;
}