This is the only kind of "secret sauce" I homebrew ->
It's all just math so I'd be happy to share.
Unh, except the shaders wouldn't really be helpful unless you had all of the other tangential engine code (it relies on a funky RGBA to 4D coord "hashing" texture generator, etc) which would just cloud things up, I'm sure.
So, I just cleaned up this
Java implementation of just the noise functions which should be pretty straightforward to port to other languages. I've got a half finished JS implementation that needs some JavaScript specific optimizing that I'll post someday.
Basically, you just request a noise sample from a 2D, 3D, or 4D coordinate, and you get back a value from -1 to +1. Do more samples you get smooth fast tileable gradients, scale / shift / swap XYZWs, etc, and combine the values to make fractal noise.
Note: I remove the attribution clause from the standard MIT license, this means you don't have to mention where you got it, just include disclaimer & permission part to cover my ass. Re-implementations are all yours, no need to include any of my notices.
Edit:
Added some ASCII art to explain the shape indexing coordinate space shearing stuff.