parallax algorithm?

Huh? Parallax is not an algorithm. What do you want to do?

Maybe you should start with that paper : Parallax Mapping with Offset Limiting

This paper became very popular few years ago because it both describes well the technique as well as showing practical code examples.

Now many improvements were proposed, and you may see many other papers on the Internet, but every improvement grants image quality with losing more or less significant performance. So all in all the "old" technique described above still remains popular today. It is very easy to implement it in a pixel shader, granted your 3D engine already supports DOT3 bump mapping, and is AFAIK the fastest way of rendering parallax mapped textures.

whoops, just realized this is probably not a opengl related question. and also sorry for calling parallax an algorithm :P

what i meant was a description/article about it, so you hit the nail right on the head vincoof thank you!!

cheers