Beamer Article and Org Mode

I generate LaTeX Beamer lecture slides and handouts from a single Org mode data file.¹ The handouts include the information on the slides plus some extra explanation. I like to draw a box around the slide information so that students can easily differentiate the slides from the notes. I have scripts that export the Org file, generate the LaTeX files, then create the PDF's. Everything seemed to work well so far, or at least I hadn't noticed anything that wasn't working. I'm teaching a course this summer that covers the same material in one day that I usually cover in three days during a regular semester. Ordinarily, I structure the presentation using only sections and slides, but stitching three of them together required adding subsections to keep everything clear. Adding subsections shouldn't have been a problem, it's just a matter of changing one line in the Org header from

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#+OPTIONS: H:3

to

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#+OPTIONS: H:2

Unfortunately, this messed up the nice boxes around the slide material on the handouts. Suddenly, the boxes had completely disappeared. I didn't understand why until I started looking at the LaTeX files. It turned out that I had been using tcolorbox to draw boxes around every block environment. Once I made the change, the slides were in a frame environment on the handouts, as they should have been. Easy fix, or so I thought — just change "block" to "frame" in the tcolorbox command. That brought the boxes back, but only around the slide titles, not around the slide contents.

After many completely unproductive Internet searches, I stumbled on the problem. Org Beamer exports a slide to this LaTeX code:

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  \begin{frame}[label]{Slide Title}
    Slide contents
  \end{frame}

This is fine for everything except my lecture handouts. I found that a small change to the LaTeX file completely fixed everything, though. All I needed to do was to change the frame environment to look like this:

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  \begin{frame}[label]
    \frametitle{Slide Title}
    Slide contents
  \end{frame}

Now, the problem was getting Org mode to export the subtree to look like that. After many, many more unproductive Internet searches, I learned that new Org exports could be made from pre-existing ones using org-export-define-derived-backend. Unfortunately, I couldn't get it to work. Finally, it struck me that since I only needed to use frametitle for the handouts, a simple search and replace might be best. Adding this function to my compilation script worked:

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  (defun rlr/create-frametitle ()
    "Convert title to frametitle."
    (interactive)
    (goto-char 1)
    (while (ignore-errors
	     (re-search-forward "begin{frame}.*]"))
      (insert "\n \\frametitle"))
    )

This finds a line containing "begin{frame}", moves the point after the closing bracket of the label, inserts a new line then puts "\frametitle" before the slide title.

Here's the simple tcolorbox commands that go in the header:

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#+LaTeX_HEADER: \usepackage{tcolorbox}
#+LaTeX_HEADER: \mode<article>{\setbeamertemplate{frame begin}{\begin{tcolorbox}[colback=white, colframe=gray,]} \setbeamertemplate{frame end}{\end{tcolorbox}}}

Simple enough, and only took four days….