The patent situation well and truly sucks.Apparently, NVIDIA's Sim Dietrich described this technique to attendees of a Creative developer's forum, according to a forum post from September 2003 that's linked from the HardOCP:
We were prepared to use a two-pass algorithm that gave equivalent results at a speed hit, but we negotiated the deal with Creative so that we were able to use the zfail method without having to actually pay any cash. It was tempting to take a stand and say that our products were never going to use any advanced Creative/3dlabs products because of their position on patenting gaming software algorithms, but that would only have hurt the users.
Don't worry about it fellas. I described this technique publicly a few months before they filed the patent - hence Prior Art. Ironically, it was at a Creative Labs developer's forum. During my stencil buffer talk, I described doing shadow volumes the 'reverse' way. At the time, I didn't realize the major reason why the z fail method is better than the z pass method, although I did realize they were logically equivalent, which is why it's now known as 'Carmack's Reverse' and not 'Dietrich's Reverse'!So John gets naming rights from the gentlemanly Dietrich for first figuring out how and why this technique is particularly helpful, but Creative gets the patent from Uncle Sam for filing the appropriate paperwork. Despite the clear examples of prior art, id didn't care to tangle with Creative in court over it.
For Creative's take on the matter, see this story at the Inq.