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Carmack's Reverse Still an Issue

Creative's 2005 patent stoush with id will have ramifications for the GPL release of Doom 3.


In 2005, Creative was losing what was once a death grip on the PC audio market. Intel had released the ‘Azalia’ specification for audio, now known as Intel HD Audio. This massive leap in integrated audio rendered discrete cards all but obsolete, so Creative needed to do whatever it could to promote EAX as the premium audio solution for gamers.

In aggressively pushing EAX, it inadvertently destroyed the remaining goodwill of gamers, already annoyed by the lack of easy access to drivers, and for those with longer memories, the death of the only serious competitor in the market, Aureal. Through a notorious act of patent-enforcing bastardry, it forced id Software to include EAX support in Doom 3, despite the fact that John Carmack already had a perfectly good software audio solution.

The patent in question involves techniques for the ‘z-fail’ method of computing shadow volumes in 3D graphics engines. This is a technique widely known as ‘Carmack’s Reverse’, named after John Carmack, who used the technique in Doom 3 to cope with the sheer amount of shadows going on in the game. Unfortunately, despite this widely accepted nickname, Creative held a patent from 1999 that described a similar technique.

So, id announced that it would be incorporating support for EAX in Doom 3, and Creative graciously allowed them to use the Carmack Reverse without paying for it. Gamers were further incensed when Reverend from Beyond 3D received the following explanation from Carmack:

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.

While Carmack was certainly correct in the assessment that the situation was a win for the users, it did huge harm to Creative’s image among its core market. The whole scandal has faded from view since then, but website Doomworld has word from John Carmack about how this will effect the future GPL release of the Doom 3 source. His response was that “When we release the code (no date set), anyone that uses it would potentially be infringing. There are workarounds at a modest performance cost.”

He is most likely referring to the two-pass technique mentioned in the Beyond 3D response. Thankfully, due to Moore’s Law, something that would have had a big performance hit in 2005 will have much less of a hit nowadays. But it is still annoying that a company which has become irrelevant in gaming circles can still restrict the release of the Doom 3 source.