Game developer id Software has released Doom 3: BFG Edition’s source code to a GitHub repository under the GNU General Public License, giving the modding community a chance to tinker with the game’s engine and release their own creations without having to worry about licensing fees.

The release comes about a year after the source for the original Doom 3 title was made public, and joins other id Software code releases including Wolfenstein 3D, Quake 3 Arena, and Doom for iOS.

Doom 3: BFG Edition is an update to the company’s eight year old first-person shooter. Released only last month for the PC, PlayStation 3, and Xbox 360, BFG enhances the graphics and sound effects, adds a checkpoint save system, and includes support for 3D displays and HMDs. The game also includes the previous expansion Resurrection of Evil and a new single player expansion pack called The Lost Mission.

The source release does not contain any game data, which is still covered by the original EULA, nor functionality for integrating with Steam, for rendering Bink Videos, for rendering of stencil shadows via the "depth fail" method, a functionality commonly known as "Carmack's Reverse”, or other resources. Basically, the released source code covers the game engine for developers to work on mods or their own games.

Along with the source code the company has also released a patch for the game on steam. Among the changes are new field of vision settings, controller bind options, extra anti-cheat measures, and several bug fixes. You can read the full release notes on the official Bethesda blog.