Creative patents Carmack’s reverse

This story made the Shortbread yesterday, but we’d be remiss not to mention it more prominently. You may have been wondering what was behind the recently announced “agreement” between id Software and Creative that will bring EAX tech to DOOM 3. Turns out Creative had a software patent on the shadowing technique known, in one of the great ironies in the annals of patents and prior art, as “Carmack’s reverse.” Beyond3D managed to get a quick comment out of Mr. Carmack about patents in general and about what happened in this case:

The patent situation well and truly sucks.

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.

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:

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.

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