Doom 3 might not have blown away interactive storytelling standards when it launched on the PC back in 2004, but it definitely raised the bar as far as visuals were concerned. Despite the awesome eye candy, the Internet quickly filled with mildly disgruntled gamers who griped that they could have made a better game by, say, changing up the monster closet-filled gameplay and adding a flashlight to weapons. Well, big talkers, here’s your chance to put your money where your mouth is: yesterday, iD finally released Doom 3’s source code, nearly seven years after the game launched.
Well, to be fair, they released most of the source code: according to Gamasutra, you won’t find any game data in the files because they are still subject to the EULA. The ReadMe.txt file for the source code mentions another function that was included in the original game, but missing here:
The Doom 3 GPL source code release does not include functionality enabling rendering of stencil shadows via the “depth fail” method, a functionality commonly known as "Carmack's Reverse".