SNEK is Not an Acronym

About

snek is a simple data structure for working with vertices and edges. More importantly it is a programming pattern for applying changes to the structure. It is specifically written to be useful for a broad range of ways in which I usually write generative algorithms for creating art.

About the Name

A while back someone on twitter suggested that if Python 3 was named "snek" it would avoid naming confusion. I found that amusing at the time, and picked snek as the placeholder name for this project. I've been looking for a better name, but I haven't found one yet.

Alterations

The pattern depends on the concept of alterations. In short: an alteration is a change that will be applied to the structure at the end of a given context. alterations are further described in http://inconvergent.net/snek-is-not-an-acronym/.

I have also written about things related to snek at

• http://inconvergent.net/a-propensity-for-mistakes/ (indirectly about snek)
• http://inconvergent.net/a-method-for-mistakes/
• http://inconvergent.net/arbitrary-alterations/

Here is and example of manipulating a snek instance called snk using alterations. Alteration constructors are postfixed with ?.

; context start
(with-snek (snk)
  ; iterate vertices
  (itr-verts (snk v)
    ; move alteration
    (move-vert? v (rnd:in-circ))
    ; w will be an arbitrary
    ; vertex in snk
    (with-rnd-vert (snk w)
      ; join v and w if they are closer than d
      (if (< (edge-length snk (list v w)) d)
        ; join vertices alteration
        (join-verts? v w))))
; context end
; alterations have been applied

Custom alterations

You can define your own arbitrary alterations. There is an example of this in ex-custom-alt.lisp. I have also written about it here: http://inconvergent.net/arbitrary-alterations/

Examples

There are some examples included. They can be executed like this:

./ex-slope.lisp res/slope
./ex-lines.lisp res/lines
./ex-grp.lisp res/grp
./ex-custom-alt.lisp res/custom
./ex-hyphae.lisp res/hyphae

There is also and example of how to use the plotting functionality. This will export a simple vector file and an image to indicate the result

./ex-plot-perspective.lisp res/perspective

Notice that the resulting image will end up in res.

Usage

snek is used in

• http://moment.inconvergent.net/
• https://twitter.com/sandpaintbot
• https://twitter.com/scratchpaintbot
• https://twitter.com/cronianrings

Dependencies

This code requires Quicklisp and zpng. The path to quicklisp must be set in src/load. zpng is automatically installed via quicklisp.

• http://www.xach.com/lisp/zpng/
• https://www.quicklisp.org/beta/

Tests

There are some tests included. Run them like this:

./test.lisp
./test-snek.lisp

Stability, Changes and Versioning

This code is highly experimental on my part. It is likely to change with no warning or explanation. I will keep a note of the version number in VERSION.

On Use and Contributions

This code is a tool that I have written for my own use. I release it publicly in case people find it useful. It is not however intended as a collaboration/Open Source project. As such I am unlikely to accept PRs, reply to issues, or take requests.

Wanted Changes

• math utils as package?
• snek as package?
• Randomized order of alteration apply
• Maintain list of singly-connected vertices?