What do you use for programmatic drawing?

Gnuplot for graphs.

LaTeX PGF/TikZ for complicated diagrams.

Lines and boxes drawn with ASCII symbols (e.g., +, -, |, <, >, ^, v, /, \, ', `, etc.) using Emacs for very simple diagrams.

PGF/TikZ has considerable learning curve, so it may seem like a hassle in the initial days of learning to use it. But after mastering it once, one can unlock a lot of power and flexibility that comes with it. The PGF/TikZ manual at http://mirrors.ctan.org/graphics/pgf/base/doc/pgfmanual.pdf is really worth seeing. This manual, which is itself designed using PGF/TikZ, is a masterpiece!

https://sequencediagram.org served my needs when I needed to create some timing diagrams for the Corrily docs (e.g. [1]). The cool thing about it is that I could save the source code of the diagram alongside the document itself (as a comment in the markdown).

[1] https://docs.corrily.com/docs/price-optimization-overview

I usually use Manim for creating mathematical animations for some Mathematical courses I am writing. It’s a python library developed by the guy from 3b1b and it’s a joy to work with it.

Have you tried Pic? It might suit your needs.

http://floppsie.comp.glam.ac.uk/Glamorgan/gaius/web/pic.html

I've used pixijs.com in javascript, especially the drawing bits: https://pixijs.io/examples/#/graphics/simple.js You can export the drawn surface as an image. Not sure how if it will would work from a commandline program though.

I am using Manim for animations.

However, I am also on the lookout for a good programmatic graphics editor. I am thinking of developing my own, but time is an issue.

I have successfully also used Python libraries like this one to create some graphics:

https://pypi.org/project/svgwrite/

For Python you could use the pyglet OpenGL library to do both 2D and 3D https://github.com/pyglet/pyglet

For Scratch, the pen tool extension works really well. I was just doing a demo on this for an elementary class the other day.

I'm not using it but just in case it is useful to anybody here I would add Processing to the list. Lots of examples can be found at its website:

https://processing.org/examples

I use Ghostscript (although it doesn't do animations as far as I know, but it works for programmable drawings without animations).

P5.js[0] for animating stuff quickly.

[0]: https://p5js.org/

Graphviz for diagrams, R standard library for plots, and imageMagick for simple image creation or processing.

Javascript and canvas. You can just right click and save the image.