draw-random

A small Common Lisp program that generates abstract pictures.

draw-random draws a handful of random lines on a blank canvas. The lines partition the canvas into areas. Each area is then filled with random dots whose density decreases along a random direction chosen independently for that area. The result is written as a PNG file.

An example output of draw-random: black lines crossing a 512x512 canvas, with each delineated area stippled with blue dots fading along a different direction. — Example output (512×512): black lines, blue dots, white background.

How it works

Pick a random number of lines (6 to 8 by default), each with endpoints on the canvas border so that it fully crosses the canvas.
Rasterize the lines onto a bitmap mask using Bresenham’s algorithm.
Identify connected components of non-line pixels via 4-connected flood fill; each component is an area.
For each area, pick a random direction (a uniformly random angle) and compute, for every pixel, its projection along that direction. Normalize to [0, 1] over the area.
Place a blue dot at a pixel with probability max-density × (1 - s), so density decays linearly from one end of the area to the other.
Paint the line pixels in the line color on top.
Save the resulting image as a PNG via zpng.

Dependencies

The only external dependency is zpng, available in Quicklisp. The program has been tested with SBCL.

Usage

From a REPL with Quicklisp available:

(push #P"/path/to/com-informatimago/small-cl-pgms/draw-random/"
      asdf:*central-registry*)

(ql:quickload "com.informatimago.small-cl-pgms.draw-random")

(com.informatimago.small-cl-pgms.draw-random:draw-random
   :pathname "example.png")

All parameters are keyword arguments with sensible defaults:

(com.informatimago.small-cl-pgms.draw-random:draw-random
   :width       512
   :height      512
   :background  #(255 255 255)   ; white
   :line-color  #(0   0   0)     ; black
   :dot-color   #(0   0   255)   ; blue
   :min-lines   6
   :max-lines   8
   :max-density 0.25
   :pathname    "example.png")

Parameters

Keyword	Default	Meaning
`:width`	`512`	Canvas width in pixels.
`:height`	`512`	Canvas height in pixels.
`:background`	`#(255 255 255)`	Background color, as an RGB vector of bytes.
`:line-color`	`#(0 0 0)`	Color used to draw the lines.
`:dot-color`	`#(0 0 255)`	Color used to stipple the areas.
`:min-lines`	`6`	Lower bound on the number of random lines.
`:max-lines`	`8`	Upper bound on the number of random lines.
`:max-density`	`0.25`	Fraction of pixels stippled at the dense end of each area.
`:pathname`	`"draw-random.png"`	Output PNG file path.

Files