Manually creating a basic beamer toc

Question

For some applications, e.g. Links in mindmap as table of contents in beamer the default beamer table of contents is not flexible enough

How to manually recreate a basic beamer toc as starting point for crazy things?

Answer 1

The following code produces a rudimentary toc with much less functionality than the origional beamer toc, but it really just meant as a starting point for more complicate things that would not be possible with the default toc.

\documentclass{beamer}

\usepackage{tikz}

\setbeamercolor{subsection in toc}{fg=black}

% total number of sections %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage{totcount}
\newcounter{totalsection}
\regtotcounter{totalsection}
\AtBeginDocument{%
  \pretocmd{\section}{\refstepcounter{totalsection}}{}{}%
}%

% number of subsections per section %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage{xcntperchap}
\RegisterCounters{section}{subsection}
\newcounter{totalsubsection}
\setcounter{totalsubsection}{0}

% creating automatic label %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% based on https://tex.stackexchange.com/a/386557/36296
\AtBeginSection[]{\label{sec:\thesection}}
\AtBeginSubsection[]{\label{subsec:\thesection:\thesubsection}}
\newcounter{currentsub}
\newcounter{totsection}

% custom toc
\newcommand{\mytoc}{%
    \begingroup%
        \usebeamerfont{section in toc}%
      \usebeamercolor[fg]{section in toc}%
    \setcounter{totsection}{\number\totvalue{totalsection}}%
    \foreach \i in {1,...,\thetotsection}{%
        \hyperlink{sec:\thesection}{\nameref{sec:\i}}%
            \setcounter{currentsub}{\ObtainTrackedValueExp[\i]{section}{subsection}}%
            \par%
            \begingroup
                \usebeamerfont{subsection in toc}%
                \usebeamercolor[fg]{subsection in toc}%
                \ifnum\thecurrentsub>0%
                    \foreach \j in {1,...,\thecurrentsub}{%
                        \hspace{1cm}\hyperlink{subsec:\i:\j}{\nameref{subsec:\i:\j}}%
                        \par%
                    }%
                \fi%
            \endgroup
            \vfill
        }% loop over i
    \endgroup
}

\title{Some Title}

\begin{document}

\begin{frame}
    \mytoc
\end{frame}

\section{Section 1}
\subsection{Subsection 1a}
\frame{}
\subsection{Subsection 1b}
\frame{}
\subsection{Subsection 1c}
\frame{}

\section{Section 2}
\frame{}

\section{Section 3}
\subsection{Subsection 3a}
\frame{}
\subsection{Subsection 3b}
\frame{}
\subsection{Subsection 3c}
\frame{}

\end{document}