obsidian

Obsidian is a constraint-based system for generating technical diagrams (though you can draw other things with it, too). It lets you write terse, descriptive scripts which produce publication-quality vector or raster graphics.

I've written a little bit about Obsidian's design and use here. A follow-up post focused on using Obsidian for technical drawing is forthcoming.

The design and API are partly inspired by this blog post on an interesting (but unfortunately closed-source, and possibly abandoned) constraint-based graphic design tool.

setup

Obsidian currently only targets Python 3.7. This is because it depends on dataclasses (which were added to stdlib in 3.7) and pysmt (which may have issues on 3.8 or later).

You will also need Cairo. Depending on your platform this can be installed with apt install libcairo2, dnf install cairo-devel brew install cairo, or similar.

Obsidian's API is not even close to stable, so I haven't put it on PyPI yet.

Dev setup instructions:

$ git clone git@github.com:wootfish/obsidian.git
$ cd obsidian
$ python3.7 -m venv venv
$ source venv/bin/activate   # or activate.zsh, activate.fish, etc
(venv) $ pip install -e .
(venv) $ pysmt-install --z3

If all goes well, then (with your virtualenv active) you should be able to cd into the examples folder, run any of the scripts there, and see no errors (aside from the deprecation warning thrown by pysmt).

usage notes

The basic idea is to create some Shapes, put them into a Group, specify their juxtaposition through a list of constraints passed to that Group, and to render the Group using a Canvas.

Groups may be placed within other Groups without surprises or complications, permitting a modular design pattern where different regions of a diagram can be specified independently and then composed.

Explicit coordinates do not often get specified in Obsidian; in fact, for most images they are not necessary at all. However, just so you know: We place the origin in the top-left, with +x pointing right and +y pointing down.

(This is the convention used by most graphics editing tools; however, it is in open defiance of our graphics library, which places the origin in the bottom left with +y pointing up; I know that's how people draw x-y axes on paper and also how GL does things, but god dammit it just ain't right.)

Until we write some proper docs, the best usage guide is the examples folder. I've done my best to keep the examples terse and clear. If you have any questions, you can reach me on Twitter or elsewhere.