static <A extends Component> A centerFrame(A c) {
  Window w = getWindow(c);
  if (w != null) swing {
    var r = preferredScreenBounds();
    w.setLocation(
      r.x+(r.w-w.getWidth())/2,
      r.y+(r.h-w.getHeight())/2);
  }
  ret c;
}

static <A extends Component> A centerFrame(int w, int h, A c) {
  ret centerFrame(setFrameSize(w, h, c));
}