jamis/kaleidoscope

Generate uniform tilings (tesselations) of a plane using Wythoff constructions. Not as hard (or scary) as it sounds!
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Kaleidoscope

Kaleidoscope is a library for generating uniform tilings of a plane using Wythoff's construction (sometimes called "Wythoff's kaleidoscopic construction", hence the name of the library).

Overview

The central idea behind Wythoff's construction is the use of right triangles, which are then tiled to fill the desired area on a plane. If you place a point (called the "generator point") at the same location within each of the triangles, and then connect the points between adjacent triangles, you get a uniform tiling.

Note that there are many tilings that are non-Wythoffian, which means they cannot be generated using this method, and thus are not supported by Kaleidoscope.

Kaleidoscope does not, by itself, provide any methods for displaying these patterns; it merely generates the data structures and hands them to you. It is up to you to then render the patterns in a format of your choosing (PNG, or SVG, or whatever you have ready to hand).

Understanding Wythoff's construction

Triangles

The triangles are specified by their corners, so that if one corner has an angle of pi/4, that corner would be given the value of 4. The right angle itself (pi/2) would be 2. Because the right angle is always present, its presence is always implied, and you only need to specify the other two corners.

There are really only three types of triangles that will uniformly tile a plane:

• (4,4,2)
• (6,3,2)
• (3,6,2)

While Kaleidoscope lets you provide any triangle specification you like, the three above will give the best results.

Generator points

Within the tiling triangle, the "generator point" may be located anywhere. If you don't specify it, Kaleidoscope will set it to be the incenter of the triangle, which gives a nice pattern, but you may set it yourself using two barycentric coordinates, u and v. When u and v sum to 1, they identify a location on the hypotenuse. When either u or v is 0, they identify a location on one of the other legs of the triangle. When u and v sum to less than 1, they identify a point inside the triangle.

Usage

Generating a pattern is as simple as this:

``````require 'kaleidoscope'

pattern = Kaleidoscope::Pattern.new(6, 3)
pattern.generate! do |point|
point.x.between?(-5, 5) &&
point.y.between?(-5, 5)
end

pattern.polygons.each do |polygon|
# do something with each generated polygon
end
``````

The block given to the #generate! method determines the area of the plane that will be tiled. Points for which the block returns false will not be included in the resulting polygon set.

Credits

Huge, huge, HUGE thanks go to Sam Gratrix for his fantastic Wythoffian Uniform Tilings app (an interactive Javascript app for displaying these tilings). It's really well done, and it taught me a lot about how Wythoffian constructions work.