The tl;dr pull quote:
> [It is a] font created in a virtual environment that can simulate light falling upon any 3-D character in the set, thus eliminating the need to draw tens of thousands of shadows, one by one
http://www.cs.indiana.edu/ftp/techreports/TR136.pdf
(Also covered in his Oct. '82 article in Scientific American, Variations on a Theme as the Crux of Creativity)