Theme with a different footline for the titlepage

Question

An easy way to get a different footline for a given frame is to declare the template locally. For example, to have a footline with the text my special footline, one can write:

\documentclass{beamer}

\begin{document}

{
\setbeamertemplate{footline}{my special footline}
\begin{frame}
  \titlepage
\end{frame}
}

\end{document}

Hence, my question: Is it possible to modify a theme such that the footline automatically reads as my special footline on the title page when one enters

\begin{frame}
  \titlepage
\end{frame} 

P.S. A simple solution would be to test the number of the frame. However, it does not apply in my case since this assumes that there is necessarily a title page.

Answer 1

Here is the solution I was looking for. The same technique can be used to define a specific template (or beamer color) for the title page.

\documentclass{beamer}

\makeatletter
\def\ps@navigation@titlepage{%
  \setbeamertemplate{footline}{my special footline}% <-- define here the specific footline for the titlepage 
  \@nameuse{ps@navigation}}
\addtobeamertemplate{title page}{\thispagestyle{navigation@titlepage}}{}
\makeatother

\begin{document}

\begin{frame}
  \titlepage
\end{frame}

\end{document}

Answer 2

Just a quick and dirty hack, but basically my idea is to add the content of your special footline (in my case, I switched the colours) just at the end of the titlepage definition:

\documentclass{beamer}

\usetheme{Warsaw}

% mod. from default theme
\defbeamertemplate*{title page}{myspecial}[1][]
{
    \vbox{}
    \vfill
    \begingroup
    \centering
    \begin{beamercolorbox}[sep=8pt,center]{title}
        \usebeamerfont{title}\inserttitle\par%
        \ifx\insertsubtitle\@empty%
        \else%
        \vskip0.25em%
        {\usebeamerfont{subtitle}\usebeamercolor[fg]{subtitle}\insertsubtitle\par}%
        \fi%     
    \end{beamercolorbox}%
    \vskip1em\par
    \begin{beamercolorbox}[sep=8pt,center,#1]{author}
        \usebeamerfont{author}\insertauthor
    \end{beamercolorbox}
    \begin{beamercolorbox}[sep=8pt,center,#1]{institute}
        \usebeamerfont{institute}\insertinstitute
    \end{beamercolorbox}
    \begin{beamercolorbox}[sep=8pt,center,#1]{date}
        \usebeamerfont{date}\insertdate
    \end{beamercolorbox}\vskip0.5em
    {\usebeamercolor[fg]{titlegraphic}\inserttitlegraphic\par}
    \endgroup
    \vfill
    %%%%%%%%%% added footline from split
    \leavevmode%
    \tiny%
    \hbox{
        \hskip-1.1cm%
        \begin{beamercolorbox}[wd=.5\paperwidth,ht=2.5ex,dp=1.125ex,leftskip=.3cm plus1fill,rightskip=.3cm]{title in head/foot}%
        \usebeamerfont{author in head/foot}\insertshortauthor
    \end{beamercolorbox}%
    \begin{beamercolorbox}[wd=.5\paperwidth,ht=2.5ex,dp=1.125ex,leftskip=.3cm,rightskip=.3cm plus1fil]{author in head/foot}%
        \usebeamerfont{title in head/foot}\insertshorttitle
    \end{beamercolorbox}}%
}

\title{test title}

\setbeamertemplate{navigation symbols}{}

\setbeamertemplate{title page}[myspecial][colsep=-4bp,rounded=true,shadow=false]

\begin{document}

    \begin{frame}[plain,b]
        \titlepage
    \end{frame} 

    \begin{frame}
        normal
    \end{frame}

\end{document}