Soft shadow tutorial (& possible demo)

[msxyz]

I'm looking for an article which describes in detail the mathematic principles behind soft shadows and also a detailed tutorial on how to implement them in hardware through OpenGL. Does anybody know any good links? A quick search through Google brought up a lot of white papers and presentations, but little useful stuff.

I recall seeing an extensive tutorial on the argument with also working code code explained but I cannot find it anymore.

[MikeC]

This may help:

http://citeseer.ist.psu.edu/cis?q=soft+shadows&submit=Search+Documents&cs=1


http://www.sgi.com/products/software/opengl/examples/glut/advanced/images/softshadow.jpg

http://www.sgi.com/products/software/opengl/examples/glut/advanced/source/softshadow.c

[msxyz]

Thanks :)