I had lots of free time in between the end of my final university exams and graduation to explore some ideas that had surfaced. I decided to take the opportunity to learn some Rust at the same time (perhaps I’ll write my thoughts in another post).

I’m not sure exactly where the idea came from, but at some point when I was strolling through Bath I started to get interested in how the anatomy of pretty much any conceivable lifeform can be represented as an acyclic graph. A simple example is given by simply assigning nodes to each appendage – a human has a head, torso and four limbs. Clearly the granularity of the representation is somewhat arbitrary, and I’m still not sure what the best approach is.

For example, a creature’s neck could simply be the edge between the head and torso nodes, or a node of its own. This is partly dependent on the graph datastructure used; some libraries such as petgraph allow arbitrary weights to be assigned to both edges and nodes, favouring the former approach. And then of course we can descend down the rabbit hole further, assigning a node to each skeletal joint.

Dwarf Fortress was an obvious inspiration for choosing the right level of precision for interesting game mechanics. For example, a tree structure allows limbs to be lopped off or infections to spread realistically. Trees are also easily visualised, and can even be procedurally animated to show locomotion a la Maxis’ Spore.

It’s a general truism that given a sufficiently abstract representation with some well-defined constraints, random generation is an obvious route for fruitful distraction. Accordingly I came up with a simple way of encoding a bilateral tree as a simple string of integers – a basic genome. The genome describes the branching from the original root node, with the special control character 0 used to backtrack, allowing lots of leaves. Equivalently the generated tree is a stack of groups of leaves, which can be popped accordingly.

For example, a very basic stick-man can be represented as the genome:

[1, 2, 0, 1, 2]

where the man’s head is the root node, followed by the upper torso, arms, lower torso and legs.

Here’s a video of generating a tree in Unity and applying some simple physics constraints to get a nice layout:

The next steps are to:

  1. Determine a way to intuit how sensory organs and other meaningful entities can be placed around the anatomy to allow hands, eyes etc. to be assigned realistically.
  2. Come up with a fitness function for an evolutionary algorithm to filter out non-viable anatomies, favour less complexity and so on.