Create a hyperlink from the logo to the table of contents slide in an rmarkdown::beamer_presentation with a custom beamer theme

Question

I use a custom LaTex beamer theme in an rmarkdown::beamer_presentation. As per these SO answers (LaTex theme, colon, theme path), I used several modifications of the YAML header and beamerthemeTHEMENAME.sty. These LaTex hacks are necessary to apply the LaTex Beamer theme smoothly in the rmarkdown::beamer_presentation.

For the foot line defined in beamerouterthemeTHEMENAME.sty, it would be very nice to have a hyperlink from the logo to the table of contents slide (like the slide numbers are linked to the appendix).

What I tried: define custom foot line in beamerouterthemeTHEMENAME.sty

\mode<presentation>

...

% Foot line
\setbeamertemplate{footline}{
    \leavevmode%
    \hyperlink{toc---table-of-contents}{\includegraphics[width=12mm,trim=0mm 0.4mm 0mm 0mm]{img/my_logo.png}}   
    \hfill
    \hyperlinkappendixstart{\insertframenumber/\inserttotalframenumber}
    \vspace{3mm}
}

\mode<all>

For a complete MWE, see my SO question here.

Answer 1

In normal beamer code, you could simply attach a label to the frame, but Rmarkdown seems to be too stupid to correctly parse the square brackets in \begin{frame}[label=outline].... annoying!

As a workaround you could use something like a section name for which markdown will automatically insert a label:

---
subtitle: "Beamer presnetation with R-markdown"
institute: "some place"
date: "`r format(Sys.time(), '%B %d, %Y')`"
author: "Donald Duck"
output:
  # beamer_presentation: default
  bookdown::pdf_book:
    base_format: rmarkdown::beamer_presentation
    # includes:
    #   in_header: preamble.tex
    theme: "THEMENAME"
    latex_engine: xelatex
    toc: false
    slide_level: 2
    keep_tex: true 
header-includes:
  - \AtBeginDocument{\title{MWE}\titleframe}    
  - \AtEndDocument{\begin{closingframe}lalala\end{closingframe}}
  - \makeatletter\beamer@ignorenonframefalse\makeatother
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = FALSE)
```

## Outline {.unnumbered}

\tableofcontents

# section

## Slide with Bullets
<!-- ======================================================== -->

- Bullet 1
- Bullet 2
- Bullet 3

<!-- Appendix -->
<!-- ======================================================== -->
``` {=latex}
\end{frame}
\appendix
\begin{frame}
```

and use this target in the footline

% Footline
\setbeamertemplate{footline}{
    \leavevmode%
    \hyperlink{outline}{\includegraphics[width=12mm,trim=0mm 0.4mm 0mm 0mm]{example-image}}
    \hfill
    \hyperlinkappendixstart{\insertframenumber/\inserttotalframenumber}
    \vspace{3mm}
}