Modify position of fancyhdr footer in R markdown

Question

I have been searching to solve this issue for quite some time, but I cannot get it right. I use R markdown for creating a beamer presentation and I would like to include a footer by using the fancyhdr LaTeX package. The problem that I encounter is that the footer is not completely on each slide. I assume that it has to do something with the margins used by beamer, but I do not know how to change this.

Here is a MWE. This is the .rmd file:

---
title: "Untitled"
author: ""
date: "10 januari 2019"
output: 
  beamer_presentation:
    includes:
      in_header: preamble.tex
---

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

## R Markdown

SOME NICE TEXT

This is in the file "preamble.tex" that is specified in the YAML:

\usepackage{fancyhdr}
\pagestyle{fancy}

\lhead{}
\chead{}
\rhead{}
\lfoot{Text in footer}
\cfoot{}
\rfoot{\thepage}
\renewcommand{\headrulewidth}{0.4pt}
\renewcommand{\footrulewidth}{0.4pt}

This is how it looks. The footer is not entirely on the slide:

Thank you in advance for your help!

Answer 1

When using beamer, it's much more natural to set the footline template than try to use fancyhdr like you'd use with, for example, and article class document (or a pdf_document in R Markdown world). Changing your preamble.tex to the following:

\setbeamertemplate{footline}
{
    \leavevmode%
    \hbox{%
        \begin{beamercolorbox}[wd = .5\paperwidth, ht = 1ex, dp = 1ex, center]{author in head/foot}%
            Text in footer
        \end{beamercolorbox}%
        \begin{beamercolorbox}[wd = .5\paperwidth, ht = 1ex, dp = 1ex, center]{date in head/foot}%
            \insertframenumber{}
        \end{beamercolorbox}
    }%
    \vskip3pt%
}

\addtobeamertemplate{footline}{\begin{center}\rule{0.6\paperwidth}{0.4pt}\end{center}\vspace*{-1ex}}{}

results in this output:

which I believe is pretty close to what you want (the black bar there in the middle is just space between the slides in the PDF viewer I was using); you can tweak the footline definition until you get it precisely there.