Building Impress and PowerPoint Slides with LaTeX and Perl
Let's begin with a story. Here's what happened: my second book, coauthored with Dr Michael Moorhouse, finally was finished. I had spent an extra six months on it, which meant it now was at least six months late. I had spent every spare minute typesetting, proofreading, writing, manually converting Michael's Microsoft Word files to LaTeX, reading and then re-reading. Then, I'd proofread it all again. When it was done and dusted, I was jaded. Soon after, I received the final proof of the cover. And there it was—printed right on the back cover—a promise to provide Microsoft PowerPoint slides on the Web site for use with the text. It was too late to change the cover, which meant I was committed to providing the slides one way or another. I had forgotten that we had decided to do this at the start of the project, more than 18 months prior.
Eighteen months ago, PowerPoint was the de facto standard slide production technology within the academic community. Today, PDF is popular too. As with many in the Linux community, I already had made the move to OpenOffice.org, leaving PowerPoint behind. With 20 chapters in the book, I estimated it would take at least 20 days' effort to produce the slides manually. The thought of doing this work with PowerPoint was not something I relished. I could work within OpenOffice.org Impress, of course, and then export to PowerPoint when finished, but this idea didn't sit well with me, either. The basic problem was I knew all the content already was in the LaTeX files and having to reproduce it using a slide production application left me feeling even more drained than I already was. If only I could find a way to extract the content programmatically from my LaTeX files and populate PowerPoint slides with it—that would improve things considerably.
Searching Google resulted in frustration. Perhaps not surprisingly, details of the PowerPoint file format were hard to come by. I did find a file in Microsoft Windows Help format that described the XML standard for Microsoft Office documents, to which PowerPoint documents can be exported. Unfortunately, it was a large, complicated piece of writing. Having decided I wasn't going to get anywhere on Google, I surfed over to Comprehensive Perl Archive Network (CPAN). Perl, my programming language of choice, has been hooked up to all types of file formats and other computing forms. If anyone had played with Perl and PowerPoint, details of the work would be available on CPAN. Unfortunately, this search also drew a blank.
Then it occurred to me: if I could work with the open and widely published OpenOffice.org Impress document format, I then could export my Impress slides to PowerPoint as a last step. A quick perusal of the OpenOffice.org Web site uncovered the official XML description of the OpenOffice.org file formats. Weighing in at more than 600 pages, the standard is bigger than my book!
The XML document is well written, but it's pretty heavy going. I surfed back to CPAN to see if any other programmers had taken the time to work with OpenOffice.org formats and were gracious enough to upload their work to CPAN. This time I wasn't disappointed. Jean-Marie Gouarne of Genicorp recently had released the OpenOffice::OODoc module, a Perl interface to the OpenOffice.org formats. Given an existing document, OpenOffice::OODoc can manipulate the content, adding to, deleting from and updating the disk file as need be.
I started with a simple filter, written in Perl, that takes a LaTeX file as input and produces the slide content as output in a customized textual form. By producing a text file, I ensured that any text editor could be used to edit the output from the filter, fine-tuning the textual content as necessary. Once happy with the textual content, another filter, also written in Perl, uses the textual content to create an Impress presentation. The Impress presentation then can be opened in Impress and exported to PowerPoint and/or PDF format.
I made a conscious effort to keep my presentations as simple as possible and decided to have only three slide types. The title_slide would contain the title of the chapter at the start of the presentation file. Within the presentation, the title_slide would do double duty as a placeholder for any graphic images associated with the chapter, with one title_slide created per graphic image. The bullet_slide would contain section titles as its slide heading and subsection titles as bullet items. Finally, the sourcecode_slide would provide a mono-spaced, verbatim slide used for program listings.
I used Impress to create a three-slide presentation manually, which I called blank.sxi. Each of the created slides corresponded to each of the three slide types described in the last paragraph. I planned to clone this presentation every time I programmatically created a presentation for each of my chapters. By cloning, I'd ensure that all of the presentations conformed to a standardized look and feel.
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