static void mol_active_cb(Fl_Widget *w, void *v) {
  VMDApp *app = (VMDApp *)w->user_data();
  MolBrowser *browser = (MolBrowser *)v;
  for (int i=0; i<browser->size(); i++) {
    if (browser->selected(i+1)) {
      int molid = app->molecule_id(i);
      app->molecule_activate(molid, !app->molecule_is_active(molid));
    }
  }
}
static PyObject *activate(PyObject *self, PyObject *args) {
  int molid;
  PyObject *boolobj;
  if (!PyArg_ParseTuple(args, (char *)"iO", &molid, &boolobj))
    return NULL;

  VMDApp *app = get_vmdapp();
  Molecule *mol = app->moleculeList->mol_from_id(molid);
  if (!mol) {
    PyErr_SetString(PyExc_ValueError, (char *)"Invalid molecule id");
    return NULL;
  }
  app->molecule_activate(molid, PyObject_IsTrue(boolobj));

  Py_INCREF(Py_None);
  return Py_None;
}