website/blog/2020-06-08-svg-slides.md

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2020-06-08 00:23:21 +02:00
title: SVG + Makefile = slide deck
summary: "You don't need LibreOffice to prepare your presentation -- or: an introduction to makefiles"
published: 2020-06-02
---
Text-based slides are boring and not effective. While preparing a presentation for my intermediary
thesis' defence, I wanted to create something that would support my story better. I wanted to use
graphics instead of words so the language centres of my dear audience's brains could focus on my
speech rather than reading. Rather than importing slide-sized graphics in a GUI, I thought
a makefile would be a nice way to do the trick.
Makefiles these days are commonly used as a shell script with multiple entry points. You give it a
filename, and it will build that file if its dependencies have been changed. Traditionally
makefiles are used for C programs, but there's no reason you can't use them for any build you want.
Even this website is updated with a makefile! Want to join me and write one together?
## Writing the makefile
Putting the name of our output file in variables will make it easier to change it later.
```makefile
OUTPUT = slides.pdf
```
We'll make a list of SVGs in the current directory, and convert it into a list of PDFs targets.
Sorting is necessary to be able to place your slides like you want. The `$(:=)` construct is used
to go from `%.svg` to `build/%.pdf`.
```makefile
SLIDES ::= $(sort $(wildcard *.svg))
SLIDES_PDF ::= $(SLIDES:%.svg=build/%.pdf)
```
I love this next rule. It teaches make that it should use Inkscape if it needs to create a PDF.
`$@` refers to the target (`build/….pdf`), and `$<` refers to the first dependency (`….svg`).
Inkscape's `-A filename` option exports to PDF without opening the GUI.
**TODO: isn't there a way to automatically depend on all parent directories?**
```makefile
build/%.pdf: %.svg build
inkscape -A "$@" "$<"
```
Now we tell make that the final output can be created from the individual slides.
Make will recursively make sure that all dependencies are up to date. Because we add the SVG source
file as a dependency, it will know that the individual PDF files have to be rebuilt if their source
was changed. And if any slide was changed, the end result will be updated too. But if there was no
change, it won't. Nothing is rebuilt unnecessarily!
**TODO: DRY**
**TODO: Do we need to fix sh's space disease here?**
```makefile
$(OUTPUT): $(SLIDES_PDF)
pdfjoin $(SLIDES_PDF) -o "$@"
```
If you look at the `build/%.pdf` rule, you see that it depends on `build`. With this simple, final
rule, make will know how to create this directory.
```makefile
build:
mkdir -p "$@"
```
It is common to create a `clean` to clean up. Since `clean` is not a file, we have to mark the
target as "phony".
```makefile
.PHONY: clean
clean:
rm -rf "$(OUTPUT)" build/
```
This concludes the Makefile portion of this post.
**TODO: write about first rule being the default**
**TODO: split into 2 posts?**
## Creating and presenting slides
Create one SVG per slide, you can do that in Inkscape. Set the document size to something with the
desired aspect ratio. In my experience this is 16:9 for newer projectors and 4:3 for older models.
To use the resulting slide deck during your presentation, I can recommend
[pdfpc](https://pdfpc.github.io/). But any old PDF viewer that has a fullscreen mode will work, of
course.