r - How to adapt a LaTex beamer theme to apply it in an rmarkdown::beamer_presentation

Question

I would like to apply a LaTex beamer theme in an rmarkdown::beamer_presentation. The custom themes contains a beamerthemeTHEMENAME.sty, beamercolorthemeTHEMENAME.sty, beamerfontthemeTHEMENAME.sty, beamerinnerthemeTHEMENAME.sty, beamerouterthemeTHEMENAME.sty. If the template is sourced within my YAML header, the knitted presentation does not look very close to a beamer presentation generated straight from LaTex by applying the custom theme.

Thus, which contents of the beamertheme*.sty to modify or enhance the presentation require modification or need to be moved from the beamer theme, e.g. to template.tex and includes*?

In particular, I am struggling on using the following frame templates defined in beamerouterthemeTHEMENAME.sty: itleframe, ocframe, closingframe

For the footline defined in beamerouterthemeTHEMENAME.sty, it would be very nice to have a hyperlink from the logo to the table of contents slide (like the page numbers are linked to the appendix). An MWE is provided below. Any help is greatly appreciated.

MWE.Rmd

---
title: "MWE"
subtitle: "Beamer presnetation with R-markdown"
institute: "some place"
date: "`r format(Sys.time(), '%B %d, %Y')`"
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
---


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

# Random presentation

## TOC - Table of Contents {.unnumbered}

ableofcontents
label{contents}

## Slide with Bullets

- Bullet 1
- Bullet 2
- Bullet 3

## Apendix
appendix

beamerthemeTHEMENAME.sty

usepackage[utf8]{inputenc}

% Tizk, textpos, graphics
RequirePackage{tikz}
RequirePackage{textpos}
RequirePackage{xcolor}
RequirePackage{booktabs}

% Beamer settings
usecolortheme{THEMENAME}
useoutertheme{THEMENAME}
setbeamertemplate{navigation symbols}{}

mode<all>

beamercolorthemeTHEMENAME.sty

mode<presentation>
definecolor{THEMECOL}{RGB}{162,48,47}  % red
definecolor{THEMEgray}{RGB}{110,110,101}% gray

colorlet{titlefgcolor}{THEMECOL} % color of box
colorlet{titlebgcolor}{THEMEgray} % color of box

setbeamercolor*{title}{fg=THEMECOL}    % presentation title 
setbeamercolor*{author}{fg=THEMECOL}   % author
setbeamercolor*{date}{fg=THEMECOL} % date
mode<all>

beamerouterthemeTHEMENAME.sty

mode<presentation>

% Redefine insertshortinstitute to allow multiple lines
makeatletter

enewcommand{insertshortinstitute}{eamer@shortinstitute}
makeatother

% Title frame
defitlefigure{img/my_bg}

ewlengthitleboxwidth
setlength{itleboxwidth}{0.33extwidth}

ewcommand{itleframe}{%
    {
        setbeamertemplate{background}{
            egin{tikzpicture}
            useasboundingbox (0,0) rectangle(hepaperwidth,hepaperheight);
            ifxitlefigureempty
                fill[titlebgcolor] (6.3mm,6.4mm) rectangle (hepaperwidth-8.3mm,hepaperheight-13mm);
            else
                
ode at (current page.center) [anchor=center,yshift=-3.5mm] {includegraphics[width=hepaperwidth-19mm]{itlefigure}};
            fi
            
ode at (current page.north east) [anchor=base east, xshift=-8.3mm, yshift=-6.3mm, align=left, inner sep=0mm, font=fontsize{5.5}{6.6}selectfont] {
                insertshortinstitute
            }; 
            
ode at (current page.north west) [anchor=south west, inner sep=0mm, xshift=8.3mm, yshift=-8.6mm] {
                includegraphics[height=3.8mm]{img/my_logo}
            }; 
            end{tikzpicture}
        }
        setbeamertemplate{footline}{}
        egin{frame}[noframenumbering]
            egin{tikzpicture}
                useasboundingbox (0,0) rectangle(hepaperwidth,hepaperheight);
                
ode [
                    shift={(-11.5mm,-1.8mm)},
                    fill=titlefgcolor,
                    minimum width=0.46paperwidth,
                    minimum height=18mm,
                    anchor=west,
                    inner sep=4mm
                    ] at (current page.west) {
                        hspace*{9mm}
                        egin{minipage}{itleboxwidth}
                            
aggedright
                            usebeamerfont{title}usebeamercolor[fg]{title}inserttitle\[3mm]
                            usebeamerfont{author}usebeamercolor[fg]{author}insertauthor\
                            usebeamerfont{date}usebeamercolor[fg]{date}insertdate
                        end{minipage}          
                    };
            end{tikzpicture}
        end{frame}
    }
}

% TOC frame

ewcommand{ocframe}{%
    egin{frame}
      frametitle{Outline}
      ableofcontents
    end{frame}
}

% Section title frame
AtBeginSection[]
{
    egin{frame}
      frametitle{Outline}
      large
      ableofcontents[currentsection] 
    end{frame}
}


ewenvironment{closingframe}{
    setbeamertemplate{background}{
        egin{tikzpicture}
        useasboundingbox (0,0) rectangle(hepaperwidth,hepaperheight);
        
ode at (current page.north west) [anchor=base west, xshift=8mm, yshift=-10mm, align=left] {
            includegraphics[width=23mm]{img/my_logo.png}
        }; 
        end{tikzpicture}
    }
    setbeamertemplate{footline}{}
    addtolength{headsep}{10mm}
    egin{frame}[noframenumbering]
}%
{
    end{frame}
}%

% Footline
setbeamertemplate{footline}{
    leavevmode%
    hyperlink{contents}{includegraphics[width=12mm,trim=0mm 0.4mm 0mm 0mm]{img/my_logo.png}}
    hfill
    hyperlinkappendixstart{insertframenumber/inserttotalframenumber}
    vspace{3mm}
}

mode<all>

Answer 1

You can make the following dirty hacks to the markdown document:

• Instead of the yaml title, use AtBeginDocument{itle{MWE}itleframe} to suppress the annoying automatic title markdown inserts (which does not even uses maketitle, so one can't make any reasonable modifications) and add your custom title command

• AtEndDocument{egin{closingframe}lalalaend{closingframe}} to add your closing frame [replace lalala with whatever text you like]

• add makeatlettereamer@ignorenonframefalsemakeatother to suppress options markdown annoyingly automatically uses and which don't allow any wrappers for frames

• you can use

  ``` {=latex}
  end{frame}
  ocframe
  egin{frame}
  ```
  

  to use your ocframe macro, however I don't see much use for this, as markdown will automatically insert such frames at all reasonable places (and then a couple of more at all unreasonable places as well, just because it seems to enjoy being annoying...)

---

---
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{itle{MWE}itleframe}    
  - AtEndDocument{egin{closingframe}lalalaend{closingframe}}
  - makeatlettereamer@ignorenonframefalsemakeatother
---

# Random presentation

## TOC - Table of Contents {.unnumbered}

ableofcontents
label{contents}

``` {=latex}
end{frame}
ocframe
egin{frame}
```

## Slide with Bullets

- Bullet 1
- Bullet 2
- Bullet 3

``` {=latex}
end{frame}
appendix
egin{frame}
```
## Apendix

Now to the theme:

• if your tex distribution has been updated at one point since the dinosaurs gone extinction, then you don't need usepackage[utf8]{inputenc}. That's the default in current latex distributions. Also rmarkdown will automatically insert this.

• you don't need RequirePackage{xcolor}. Not only does beamer already load this automatically, but it will also be included in this annoyingly long list of unsuitable packages rmarkdown automatically adds to the document.

• The itleframe macro also needs a couple of modifications because the theme does abuse \ for line breaks and does not test if title, author and date macros are actually filled. Combined this will fail spectacularly...

• you might also want to use different colours for the background and the font of the title box.... I mixed a bit of white to the background to make the font visible

ewcommand{itleframe}{%
    {
        setbeamertemplate{background}{
            egin{tikzpicture}
            useasboundingbox (0,0) rectangle(hepaperwidth,hepaperheight);
            ifxitlefigureempty
                fill[titlebgcolor] (6.3mm,6.4mm) rectangle (hepaperwidth-8.3mm,hepaperheight-13mm);
            else
                
ode at (current page.center) [anchor=center,yshift=-3.5mm] {includegraphics[width=hepaperwidth-19mm]{itlefigure}};
            fi
            
ode at (current page.north east) [anchor=base east, xshift=-8.3mm, yshift=-6.3mm, align=left, inner sep=0mm, font=fontsize{5.5}{6.6}selectfont] {
                insertshortinstitute
            }; 
            
ode at (current page.north west) [anchor=south west, inner sep=0mm, xshift=8.3mm, yshift=-8.6mm] {
                includegraphics[height=3.8mm]{example-image}
            }; 
            end{tikzpicture}
        }
        setbeamertemplate{footline}{}
        egin{frame}[noframenumbering]
            egin{tikzpicture}
                useasboundingbox (0,0) rectangle(hepaperwidth,hepaperheight);
                
ode [
                    shift={(-11.5mm,-1.8mm)},
                    fill=titlefgcolor!50!white,
                    minimum width=0.46paperwidth,
                    minimum height=18mm,
                    anchor=west,
                    inner sep=4mm
                    ] at (current page.west) {
                        hspace*{9mm}
                        egin{minipage}{itleboxwidth}
                            
aggedright
                            usebeamerfont{title}usebeamercolor[fg]{title}inserttitlepar
                            usebeamerfont{author}usebeamercolor[fg]{author}insertauthorpar
                            usebeamerfont{date}usebeamercolor[fg]{date}insertdate
                        end{minipage}          
                    };
            end{tikzpicture}
        end{frame}
    }
}

For the footline, use the hyperlink target that is created by your toc section

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

[I guess the number of times I used annoying in this answer shows how much more difficult rmarkdown makes a job that would have taken 2 seconds in a normal beamer document]