\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{takahashi}[2013/06/25 Takahashi method for beamer]

%   Copyright (c) 2008-2013, Chung-chieh Shan.

%   This program is free software; you can redistribute it and/or modify
%   it under the terms of the GNU General Public License as published by
%   the Free Software Foundation; either version 2 of the License, or
%   (at your option) any later version.

%   This program is distributed in the hope that it will be useful,
%   but WITHOUT ANY WARRANTY; without even the implied warranty of
%   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
%   GNU General Public License for more details.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% Our main command \takahashi takes an optional overlay specification
% (for the frame), an optional argument (frame options, defaulting to
% "plain"), and a mandatory argument (the contents of the frame).
\newcommand<>{\takahashi}[2][plain]{%
  \toks0={#1}%
  \toks2={\begin{frame}#3}%
  \edef\next{\the\toks0 }%
  \ifx\next\@empty
    \edef\next{\the\toks2 }%
  \else
    \edef\next{\the\toks2 [{\the\toks0 }]}%
  \fi
  \next
    \aftergroup\aftergroup\aftergroup\beamer@takahashi
    \resizebox\hsize!{#2}%
  \end{frame}%
}

% Define \takahashi@shrinkframebox, a variant of \beamer@shrinkframebox
% that centers the frame horizontally and does not depend on
% \beamer@shrinkpercentage.
\def\takahashi@shrinkframebox{%
  \@tempdima=\ht\beamer@framebox
  \advance\@tempdima\dp\beamer@framebox
  \ifdim\@tempdima>\beamer@frametextheight
    \@tempcnta=\@tempdima
    \divide\@tempcnta by 65536
    \@tempdimc=\beamer@frametextheight
    \divide\@tempdimc by\@tempcnta
    \edef\beamer@factortemp{\strip@pt\@tempdimc}%
    \setbox\beamer@framebox=\vbox to\beamer@frametextheight{%
      \begin{pgfpicture}{-.5\wd\beamer@framebox}{-\beamer@frametextheight}{0pt}{0pt}
        {\pgftransformscale{\beamer@factortemp}%
          \pgftext[top]{\box\beamer@framebox}}%
      \end{pgfpicture}%
    }%
  \fi
}

% Takahashi slides always enable the frame option "shrink" with
% \takahashi@shrinkframebox in place of \beamer@shrinkframebox.
\def\beamer@takahashi{%
  \beamer@shrinktrue
  \let\beamer@shrinkframebox\takahashi@shrinkframebox
}

% Patch beamer's implementation of the ignorenonframetext option
% (i.e., the \mode* command) so that \takahashi is not ignored.
\toks0={\ifx\beamer@nexttoken\takahashi\let\next=\beamer@stopoutsidemode\fi}%
\toks2=\expandafter{\beamer@treat}%
\edef\beamer@treat{\the\toks0 \the\toks2 }%

% Tested with beamer 3.07:
% \documentclass{beamer}
% \usepackage{takahashi}
% \usepackage{calc}
% \setbeamersize{text margin left = 0pt, text margin right = 0pt}
% \begin{document}
% \takahashi{Test \onslide<2>{some more}}
% \takahashi<1>[label=repeat]{\frametitle{Title here}Test \onslide<2>{some more}}
% \againframe<2>{repeat}
% \takahashi{$_g$\!\vrule depth.2pt height.2pt \vrule}
% \takahashi[]{\frametitle{Title here}$_g$\!\vrule depth.2pt height.2pt \vrule}
% \takahashi{\raisebox{0pt}[\height+1pt][\depth+1pt]{!}}
% \end{document}