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TLDR org mode + graphviz

Published 2019-05-21, last edit 2020-01-15

Org mode is pretty cool. Directed graphs are pretty cool. Let’s see how they go together.

1. Org mode #

After installing the graphviz package, you will have the dot command. If you use it in with an org mode source block like so:

#+BEGIN_SRC dot :file ./dot-example.png  :cmdline -Kdot -Tpng
digraph {
    a -> b
}
#+END_SRC

You can eval the block with C-c C-c and then view it inline in emacs by using org-toggle-inline-images.

These blocks also export! Just like in this page itself!

digraph {
    a -> b
}

2. The Dot language #

The dot language spec can be found here. I don’t find that too helpful on it’s own, so here are some notes:

Primitives that matter:

a node is a bubble/self contained item that will be connected.
an edge is the line that connect nodes.
a graph is a the relation as a whole.

A list of attributes that can be applied to these can be found here: https://www.graphviz.org/doc/info/attrs.html

Some nice node options can be seen here: https://www.graphviz.org/doc/info/shapes.html#polygon

Here is an example that shows how attributes are set and some defaults I like:

#+BEGIN_SRC dot :file ./dot-example.png  :cmdline -Kdot -Tpng
digraph {
    // config:
    // TBLR, top bottom left right, the direction of the graph.
    graph [rankdir=TB];
    // you can have multiple attrs per statement
    graph [dpi=150 splines=ortho];
    edge[decorate=true];
    node [shape=box];

    // definitions:
    // nb: setting definitions on their own is useful in larger graphs
    computer [label=computer];
    // quotes are optional, I'm using them when there are spaces
    phone [label="android phone"];
    router [label=router];

    // record syntax: | for horizontal, {|} for vert
    internet [shape=record label="{internet|cat pictures}"]

    // relations:
    computer -> router;
    phone -> router [label="wifi"];
    router -> internet [dir=both];
}
#+END_SRC

digraph {
    // --- config
    graph [rankdir=TB]; // TBLR, top bottom left right, the direction of the graph.
    graph [dpi=150 splines=ortho]; // you can have multiple attrs per statement
    edge[decorate=true]
    node [shape=box];

    // --- definitions
    // nb: setting definitions on their own is useful in larger graphs for standalone attribute setting
    computer [label=computer];
    // quotes are optional, I'm using them when there are spaces
    phone [label="android phone"];
    router [label=router];

    // record syntax: | for horizontal, {|} for vert
    internet [shape=record label="{internet|cat pictures}"]

    // --- relations
    computer -> router;
    phone ->router [label="wifi"];
    router ->internet [dir=both];
}