id Software’s co-founder John Carmack (photo ©Official GDC) promised it and now he did it: the sources of the id Tech 4 graphics engine – the Doom 3 one to be clear – were released as free / open source software under the GPL 3 license and are available on GitHub. The rest of the game remains a company’s property so if you want to play Doom 3 you must buy it.

Over the years John Carmack has created what is now a tradition of offering the graphics engines of old games to the community as free software when a game comes out using a new graphics engine. Last August at QuakeCon 2011 Carmack confirmed that the source of Doom 3 graphics engine would be released within the year following the release of Rage, the game based on the new id Tech 5 graphics engine.

After the August announcement John Carmack awaited only the lawyers approval because legal issues must always be kept in mind and this resulted in a delay when a few days ago a problem of this type came out. The code used for the stencil buffer implementation of shadow volumes uses a Creative Labs patent for which id Software has a license but obviously can’t release it as free software.

Faced with this problem John Carmack didn’t pull back and rewrote the code used under license very quickly because in the end he only had to add four lines of code and change two others. Carmack himself commented on Twitter that this is a demonstration of the idiocy of the patent.

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The release of the id Tech 3 game engine – the Quake III one to be clear – took place in 2005 created a large ecosystem of many free / open source games that were created over the years. I won’t make names because now there are many of them and surely I’d forget some but thanks to the fact that the Internet at that point was widely used, people created communities to develop various games based on derivatives of the id Tech 3 game engine. In fact over time the engine too has been improved.

It’s likely that the release of the id Tech 4 graphics engine’s sources will lead to the evolution of the free FPS games ecosystem so over the next months new versions of at least some of them will be developed to use it instead of the old one. There’s also to be expected that new games will be developed becase this ecosystem is dynamic and there are often news.

Obviously it will take some time to see something new because free game developers will have to familiarize with the id Tech 4 graphics engine and adapt the elements of their games to it or create new ones. For now, thank you John Carmack!