Bethesda has made a major announcement through its wholly-owned id Software subsidiary: the release of the source code for Doom 3 BFG Edition under an open-source licence.
The release, designed to allow the game to be modded on a far more fundamental level than most as well as making the latest version of the Doom 3 engine available for third-party developers to use in their games, follows id Software's tradition of releasing older versions of its game engines for free under the GNU General Public Licence. Designed for open-source efforts, the GPL allows users to make use of id Software's engine without paying a penny in royalties or licence fees - but only if they agree to release any modifications they make to the engine available under the same open-source licence.
The GPL is a source of much confusion in the software development world, much of it promulgated by closed-source software companies spreading a form of propaganda known as Fear, Uncertainty and Doubt (FUD.) Any GPL-licensed id Software engine - or any other software released under the GPL - can be used to create a closed-source, proprietary game which can be sold for profit. The licence only requires that the source code for the GPL-licensed portions, plus any modifications made therein, is published under the same licence - not the entire source code tree for the whole game.
With that clarification out of the way: id Software's release of the Doom 3 BFG engine is based on the company's upgrade to its eight year old first-person shooter engine. Released last month, the BFG Edition boosts the graphical quality of the engine, improves audio quality and adds support for 3D monitors and head-mounted displays. All of these features are brought across to the open-source version, but that doesn't mean you're getting the game for free: the source code covers the engine, but includes no game content. In other words: if you want to play Doom 3, you need to go out and buy Doom 3.
The engine released under the GPL also excludes some proprietary code used in the full retail release, notably the Bink Video Player code used for intro and outtro movies, Steam integration and a method of rendering stencil shadows developed by id co-founder John Carmack known as 'Carmack's Reverse.'
Despite its age, and the exclusion of certain aspects, the source code release is likely to be welcomed by the open-source community. With the Doom 3 BFG Edition source available, developers can now work on creating cross-platform games based on the engine without having to worry about licensing fees or issues with making their work available under an open-source licence should they so wish. It also provides a shot in the arm for developers looking to create native Linux games, alongside the release of the cross-platform Unity 4 game engine and its official support for Linux earlier this month.
The Doom 3 BFG Edition source code can be downloaded from id Software's GitHub repository