WebGL Shader demos - GPU rendering shader experiments with procedural 3D scene generation using ray marching and distance field (also known as 'sphere tracing') rendering techniques.
by Kevin Roast - see http://www.kevs3d.co.uk/dev/shaders/ for live demos and screenshots.
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Lots of code/ideas for these come from reading:
http://www.iquilezles.org/www/material/nvscene2008/rwwtt.pdf
http://www.pouet.net/topic.php?which=7931&page=1
http://www.pouet.net/topic.php?which=7920&page=1
http://iquilezles.org/www/articles/distfunctions/distfunctions.htm
If you want to understand this stuff read through the PDF and pouet.net links above