int func(Snapshot& ss_pre, Snapshot& ss_cur)
{

  Mat2f& flow = ss_cur.le.pre2cur_optflow;
  Matx33d& R = ss_cur.le.R;

  if (flow.empty() || disparity_pre.empty() || disparity_cur.empty())
    return 0;
  Size imgsize = flow.size();
  if (imgsize != disparity_pre.size())
    return 0;
  if (imgsize != disparity_cur.size())
  ...
    return 0;
}