How to center the titleframe in Hannover theme (beamer)?

Question

I am using the Hannover theme in beamer and I am using the title frame as plain

\documentclass{beamer}
\mode<presentation>
{
  \usetheme{Hannover}%{CambridgeUS}%
  \setbeamercovered{transparent}
}

\title[Title]{Centering Title frame}
\author[Gopi]{Gopi}

\begin{document}
\begin{frame}[plain]
    \titlepage
    \begin{figure}
    \begin{center}
        \includegraphics[scale=0.3]{logo}
    \end{center}
    \end{figure}
\end{frame}
\end{document}

Because it was not obvious on the first picture (white on white, I have added the same picture without the option "plain" on the frame). My point is that I would like that with the option plain the frame forget about the hannover theme and centers the whole frame.

I tried to put a \hspace{-xpt} before the frame but it did not seem to work.

Answer 1

You could \hoffset to move the content of the frame to the left, by the half amount of the sidebar width:

\begingroup
\makeatletter
\setlength{\hoffset}{-.5\beamer@sidebarwidth}
\makeatother
\begin{frame}[plain]
    \titlepage
    ...
\end{frame}
\endgroup

I used \begingroupand \endgroup to limit the effect of the change to \hoffset to just this frame. \makeatletter and \makeatletter are necessary for accessing the internal macro \beamer@sidebarwidth.