void setVisibilityFlags(BitSet bs) {
    /*
     * set all fixed objects visible; others based on model being displayed
     * 
     */
    for (int i = meshCount; --i >= 0;) {
      Mesh mesh = meshes[i];
      mesh.visibilityFlags = (mesh.visible && mesh.isValid
          && (mesh.modelIndex < 0 || bs.get(mesh.modelIndex)
          && (mesh.atomIndex < 0 || !frame.bsHidden.get(mesh.atomIndex))
          ) ? myVisibilityFlag
          : 0);
    }
  }