Absurdist Arcana Ben Weintraub's blog

Rendering Graphviz in your terminal

This post was inspired by a Twitter thread by @thingskatedid:

You should read the whole thread, there are lots of beautiful examples! Her main point is that you should enable your programs to dump their internal state representations visually. Graphviz is a convenient way to do this, since it’s easy to generate and read, and handles the actual rendering for you, but it can feel clunky to repeatedly cycle through the following workflow:

  1. Make code change
  2. Run your program (with flags to dump its internal state in Graphviz form)
  3. Redirect output to a temporary .dot file
  4. Remember the right Graphviz incantation to turn the .dot file into a .png or something (dot -T png in.dot >out.png, FWIW, but it took me years to commit that to memory)
  5. Open the resulting .png in your graphics viewer of choice

Kate talks about how to shorten this feedback cycle in this thread. This is just my distillation of her suggestions.

I use a terminal called kitty which, among other things, offers the ability to display high-quality graphics inline. The kitty documentation explains how to do it:

kitty +kitten icat path/to/some/image.png

That’s a bit wordy, so I’ve created a shell alias with the same name as Kate’s (idot), like this:

alias idot="dot -T png | kitty +kitten icat"

Now I can take some program that emits Graphviz, and just pipe it to idot, like this:

echo 'digraph { rankdir=LR; a -> b -> c }' | idot

Accommodating dark terminal background colors

If you use any terminal background color other than white, you’ll find that by default, your graphs don’t look as nice as Kate’s examples:

A screenshot showing Graphviz rendered in the terminal, with a white background

To remove the background colors and make the text, borders, and edges white, you can set a few attributes:

digraph {
  node [color=white, fontcolor=white]
  edge [color=white]

  // ... the rest of your graph ...

If you don’t want to bother with setting these in every chunk of dot you produce, you can modify your idot alias to set them as defaults, using the -G, -N, and -E flags to dot to set default graph, node, and edge attributes on the command line, like this:

alias idot="dot -Gmargin=0.7 '-Gbgcolor=#ffffff00' -Gcolor=white -Gfontcolor=white -Ncolor=white -Nfontcolor=white -Ecolor=white -T png | kitty +kitten icat"

A screenshot showing Graphviz rendered in the terminal, with a transparent background and white text / lines

You can also throw whatever other defaults you like into your alias. Check out my previous post about making Graphviz’s output prettier for some ideas.