119 lines
4.6 KiB
Markdown
119 lines
4.6 KiB
Markdown
title: SVG + makefile = slide deck
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summary: "You don't need LibreOffice to prepare your presentation -- or: an introduction to makefiles"
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published: 2020-06-02
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---
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Text-based slides are boring and not effective.
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While preparing a presentation for my intermediary thesis' defence, I wanted to create something that would support my story better.
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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.
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Rather than importing slide-sized graphics in a GUI, I thought a makefile would be a nice way to do the trick.
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Makefiles these days are commonly used as a shell script with multiple entry points.
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But they can do much more than that!
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You give it a filename, and it will build that file if its dependencies have been changed.
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Traditionally makefiles are used for C programs, but there's no reason you can't use them for any build you want.
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Even this website is built by a makefile!
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Want to join me and write one together?
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## Writing the makefile
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Putting the name of our output file in variables will make it easier to change it later.
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```makefile
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OUTPUT = slides.pdf
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```
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We'll make a list of SVGs in the current directory, and convert it into a list of PDF targets.
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Sorting is necessary to put your slides in the order you want.
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The `$(:=)` construct is used to go from `%.svg` to `build/%.pdf`.
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```makefile
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SLIDES ::= $(sort $(wildcard *.svg))
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SLIDES_PDF ::= $(SLIDES:%.svg=build/%.pdf)
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```
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I love this next rule.
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It teaches *make* that it should use Inkscape if it needs to create a PDF.
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`$@` refers to the target (`build/….pdf`), and `$<` refers to the first dependency (`….svg`).
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Inkscape's `--export-pdf filename` option exports to PDF without opening the GUI.
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**TODO: isn't there a way to automatically depend on all parent directories?**
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```makefile
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build/%.pdf: %.svg build
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inkscape --export-pdf "$@" "$<"
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```
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Now we tell *make* that the final output can be created from the individual slides (`$(SLIDES_PDF)`) by calling pdfjoin.
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*Make* will recursively make sure that all dependencies are up to date.
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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.
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And if any slide was changed, the end result will be updated too.
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But if there was no change, it won't; nothing is rebuilt unnecessarily!
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**TODO: DRY**
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**TODO: Do we need to fix sh's space disease here?**
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```makefile
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$(OUTPUT): $(SLIDES_PDF)
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pdfjoin $(SLIDES_PDF) -o "$@"
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```
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If you look at the `build/%.pdf` rule, you see that it depends on `build`.
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With this rule, *make* will know how to create this directory.
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```makefile
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build:
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mkdir -p "$@"
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```
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It is common to create a `clean` to clean up.
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Since `clean` is not a file, we have to mark the target as "phony".
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Failing to do so would result in **TODO how to finish this sentence?**
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```makefile
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.PHONY: clean
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clean:
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rm -rf "$(OUTPUT)" build/
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```
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One more thing: the default target, for when you call *make* without arguments, is the first one in the makefile (with [some caveats][gmake_docs_targets]).
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You could override this with `.DEFAULT_GOAL := your_target_name_here`, but it's just as easy to reorder the rules, which is what I've done in the summary below.
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[gmake_docs_targets]: https://www.gnu.org/software/make/manual/html_node/Goals.html "Goals – GNU make documentation"
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This is the finished makefile:
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```makefile
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OUTPUT = slides.pdf
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SLIDES ::= $(sort $(wildcard *.svg))
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SLIDES_PDF ::= $(SLIDES:%.svg=build/%.pdf)
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$(OUTPUT): $(SLIDES_PDF)
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pdfjoin $(SLIDES_PDF) -o "$@"
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build/%.pdf: %.svg build
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inkscape --export-pdf "$@" "$<"
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build:
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mkdir -p "$@"
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.PHONY: clean
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clean:
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rm -rf "$(OUTPUT)" build/
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```
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**TODO: write about first rule being the default**
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**TODO: split into 2 posts?**
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## Further help with *make*
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I'm using *GNU make* and I'll admit I don't know if this works in other flavours.
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GNU's documentation is installed on my system and accessible with `info make` (<kbd>tab</kbd> to jump to next link, <kbd>enter</kbd> to activate it, <kbd>l</kbd> to return to previous screen, <kbd>Shift+h</kbd> for help).
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When online you can also use the [online documentation][gmake_docs].
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[gmake_docs]: https://www.gnu.org/software/make/manual/html_node/index.html "GNU make documentation"
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## Creating and presenting slides
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Create one SVG per slide, you can do that in Inkscape.
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Set the document size to something with the desired aspect ratio.
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In my experience this is 16:9 for newer projectors and 4:3 for older models.
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To use the resulting slide deck during your presentation, I can recommend [pdfpc](https://pdfpc.github.io/).
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But any old PDF viewer that has a fullscreen mode will work, of course.
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