SNEK-A System for Making Generative Systems

About

This library is specifically written to be useful for a broad range of ways in which I create art using various generative algorithms.

In short snek is four things:

1. A simple (graph) data structure for working with vertices and edges The structure is named snek; the name is explained below. This structure is combined with a programming pattern for applying changes to the structure. The pattern relies on alterations, see below.

2. A series of useful data structures and tools. E.g. a 2D vector vec, a package for generating different kinds of random numbers: rnd, as well as tools for handling colors (pigment), splines (bzspl), and various vector an path functionality (math, lin-path).

3. A tool for drawing things called sandpaint. sandpaint uses random sampling to draw its primitives. This creates a fairly distinct and gritty look in many cases.

4. A tool for drawing svg files (draw-svg). Mainly svg files that are good for plotting.

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 https://inconvergent.net/2017/snek-is-not-an-acronym/.

I have also written about things related to snek at

• https://inconvergent.net/2017/a-propensity-for-mistakes/ (indirectly about snek)
• https://inconvergent.net/2017/a-method-for-mistakes/
• https://inconvergent.net/2017/arbitrary-alterations/
• https://inconvergent.net/2017/grains-of-sand/

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

; context start
(snek:with (snk)
  ; iterate vertices
  (snek:itr-verts (snk v)
    ; move alteration
    (snek:move-vert? v (rnd:in-circ 1d0))
    ; w will be an arbitrary
    ; vertex in snk
    (snek:with-rnd-vert (snk w)
      ; join v and w if they are closer than d
      (if (< (snek:edge-length snk v w) d)
        ; join vertices alteration
        (snek:add-edge? v w))))
; context end
; alterations have been applied

You can also manipulate the state directly. These functions are postfixed with !. Eg. (snek:move-vert! ...).

Examples

There are some examples included. All examples are in the examples folder.

If you don't provide a filename (with full or relative path) as the first argument, the resulting file will be named ./tmp.png.

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: https://inconvergent.net/2017/arbitrary-alterations/

Usage

I use snek for most of the work that I post online (https://twitter.com/inconvergent). Both for generating raster images as well as vector images for plotter drawings.

Here are some plotted examples:

• https://inconvergent.net/2017/spline-script-plots/
• https://inconvergent.net/mechanical-plotter-drawings/
• https://inconvergent.net/mechanical-plotter-drawings/3/
• https://inconvergent.net/mechanical-plotter-drawings/5/

Dependencies

This code requires libpng-dev, Quicklisp, zpng, cl-svg and cl-png. The path to quicklisp must be set in src/load. zpng, cl-svg and cl-png are automatically installed via quicklisp.

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

Tests

There are some tests included, see the test folder.

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 src/load.lisp.

Thanks

I would like to thank:

• https://twitter.com/RainerJoswig
• https://twitter.com/paulg
• https://twitter.com/jackrusher

Who have provided me with useful hints and code feedback.