Write initial SVG slide article

blog/svg-slides.md

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+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.