http://github.prideout.net/coordinate-fields/

https://briansharpe.wordpress.com/2011/12/01/optimized-artifact-free-gpu-cellular-noise/
http://www.rhythmiccanvas.com/research/papers/worley.pdf
http://webstaff.itn.liu.se/~stegu/GLSL-cellular/GLSL-cellular-notes.pdf

http://www.iquilezles.org/www/articles/voronoise/voronoise.htm
http://www.iquilezles.org/www/articles/smoothvoronoi/smoothvoronoi.htm
http://www.iquilezles.org/www/articles/voronoilines/voronoilines.htm