static PyObject *skip(PyObject *self, PyObject *args) {
  int value = 0;
  if (!PyArg_ParseTuple(args, (char *)"|i",&value))
    return NULL;
  
  VMDApp *app = get_vmdapp();
  if (value > 0) { 
    app->animation_set_stride(value);
  }
  return PyInt_FromLong(app->anim->skip()); 
}
static void step_cb(Fl_Widget *w, void *v) {
  Fl_Counter *counter = (Fl_Counter *)w;
  VMDApp *app = (VMDApp *)v;
  app->animation_set_stride((int)counter->value());
}