[Tex/LaTex] Latex Beamer: allowframebreaks with footnotes

beamerfootnotes

I created a simple latex beamer document shown below:

\documentclass{beamer}

\usepackage{default}

\begin{document}

\begin{frame}[allowframebreaks]\frametitle{Pages}
    \begin{itemize}
        \item First page\footnote{some text}
    \end{itemize}
\newpage
    \begin{itemize}
        \item next page
    \end{itemize}
\end{frame}
\end{document}

It uses a frame with the attribute allowframebreaks.
There is a footnote on the first page, but it is printed on the last page of the frame sequence.
I know that this is the specified target behaviour, but is it possible to change this? I would like to have the footnote on the same slide where it is supposed to be.

Thank You.

Best Answer

The procedure of Beamer dealing with allowframebreaks is as follows

  • collect all materials on the page (including footnotes);
  • typeset materials and put them into a \vbox called \beamer@framebox;
    • at the same time, footnotes is put into a box called \beamer@footins;
  • if \beamer@framebox is less than one page, shipout this box;
    • if not, \vsplit the box and shipout one page;
    • loop until \beamer@framebox is empty;
  • attach \beamer@footins at the last page.

The lesson we learn from the preceding procedure is that we do not know which footnoteitem belongs which page. So we have three choices

  • put all footnote on the last page; this is the default behavior;
  • put all footnote on the first page; this is stupid;
  • put all footnote on every page; this is worth a try.

The following is the original definition

\def\beamer@autobreakframebox{%
  \global\setbox\beamer@splitbox=\box\voidb@x%
  \ifbeamer@autobreak%
    % Ok, frame was overful -> split it!
    \setbox\@tempboxa=\vsplit\beamer@framebox to\beamer@autobreakfactor\textheight%
    \global\setbox\beamer@splitbox=\box\beamer@framebox%
    \@tempdima=\ht\beamer@splitbox%
    \ifdim\@tempdima<\beamer@autobreaklastheight%
      \global\beamer@autobreaklastheight=\@tempdima\relax%
    \else%
      \setbox\@tempboxa=\vbox{\unvbox\@tempboxa\unvbox\beamer@splitbox}%
      \global\setbox\beamer@splitbox=\box\voidb@x%
    \fi%
    \setbox\beamer@framebox=\vbox to\textheight{\unvbox\@tempboxa%
      \vskip\beamer@framebottomskipautobreak%
      \ifvoid\beamer@splitbox%
        \ifvoid\beamer@footins%
        \else%
          \begingroup
            \usebeamercolor*[fg]{footnote}%
            \footnoterule%
            \unvbox \beamer@footins%
            \global\setbox\beamer@footins=\box\voidb@x%
          \endgroup  
        \fi%
      \fi%
      \beamer@exitcode%
    }%
  \else%
    \setbox\beamer@framebox=\vbox to\textheight{\unvbox\beamer@framebox%
      \vskip\beamer@framebottomskip%
      \ifvoid\beamer@footins%
      \else%
        \begingroup
          \usebeamercolor*[fg]{footnote}%
          \footnoterule%
          \unvbox \beamer@footins%
          \global\setbox\beamer@footins=\box\voidb@x%
        \endgroup 
      \fi%
      \beamer@exitcode}%
    \global\setbox\beamer@footins=\box\voidb@x%
  \fi%
  }

And we can modify the footnote part as follows

\def\beamer@autobreakframebox{%
  \global\setbox\beamer@splitbox=\box\voidb@x%
  \ifbeamer@autobreak%
    % Ok, frame was overful -> split it!
    \setbox\@tempboxa=\vsplit\beamer@framebox to\beamer@autobreakfactor\textheight%
    \global\setbox\beamer@splitbox=\box\beamer@framebox%
    \@tempdima=\ht\beamer@splitbox%
    \ifdim\@tempdima<\beamer@autobreaklastheight%
      \global\beamer@autobreaklastheight=\@tempdima\relax%
    \else%
      \setbox\@tempboxa=\vbox{\unvbox\@tempboxa\unvbox\beamer@splitbox}%
      \global\setbox\beamer@splitbox=\box\voidb@x%
    \fi%
    \setbox\beamer@framebox=\vbox to\textheight{\unvbox\@tempboxa%
      \vskip\beamer@framebottomskipautobreak%
      \ifvoid\beamer@footins%                          MODIFIED
      \else%                                           MODIFIED
        \begingroup%                                   MODIFIED
          \usebeamercolor*[fg]{footnote}%              MODIFIED
          \footnoterule%                               MODIFIED
          \unvcopy \beamer@footins%                    MODIFIED
        \endgroup%                                     MODIFIED
      \fi%                                             MODIFIED
      \ifvoid\beamer@splitbox%                         MODIFIED
          \global\setbox\beamer@footins=\box\voidb@x%  MODIFIED
      \fi%                                             MODIFIED
      \beamer@exitcode%
    }%
  \else%
    \setbox\beamer@framebox=\vbox to\textheight{\unvbox\beamer@framebox%
      \vskip\beamer@framebottomskip%
      \ifvoid\beamer@footins%
      \else%
        \begingroup
          \usebeamercolor*[fg]{footnote}%
          \footnoterule%
          \unvbox \beamer@footins%
          \global\setbox\beamer@footins=\box\voidb@x%
        \endgroup 
      \fi%
      \beamer@exitcode}%
    \global\setbox\beamer@footins=\box\voidb@x%
  \fi%
  }

Then we achieve the following

PS. the strange/scary jumping phenomenon is discussed here: beamer: allowframebreaks option and vertical spacing when using lists (itemize, enumerate, ...)

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