early to mid 1990s, and free games started to make the switch themselves. Tuxedo T. Penguin: A Quest for Herring by Steve Baker, a game featuring the Linux mascot Tux and introducing the PLIB library, was an early example of a three-dimensional free software game. He and his son Oliver would later create other popular 3D free games and clones such as TuxKart and contribute to those by other developers such as Tux Racer. BZFlag pre-dates all of these, inspired by Battlezone and started in 1992 and released in 1993. The OpenGL specification provided a foundation for hardware acceleration since 1992, primarily through the free Mesa implementation since 1995, and later complimented by Vulkan since 2016. The Direct3D API has also been made available on free operating systems via compatibility layers such as WineD3D and DXKV. The Glide API was also made open source following the dissolution of 3dfx in 2002. The Genesis3D engine project, Crystal Space and Cube also spawned other 3D free software engines and games, later joined by the likes of Irrlicht, OGRE, Retribution, Panda3D, Castle, and Cafu. FlightGear, YSFlight, and GL-117 are also good examples, first started in 1997, 1999 and 2003 respectively (and the latter eventually forked as Linux Air Combat), especially noting that they are not first-person shooters but flight simulators. The games Yo Frankie! and Sintel The Game were developed by the Blender Foundation to showcase the abilities of the Blender modelling tool and the erstwhile Blender Game Engine. id Software, an early entrant into commercial Linux gaming, would also prove to be an early supporter of free gaming when John Carmack released the source code for Wolfenstein 3D in 1995 and Doom in 1997, first under a custom license and then later the GNU General Public License (GPL) in 1999 (later termed id Tech 1). This was followed by the release of Quake engine in 1999, the Quake II engine in 2001 (both known as id Tech 2), id Tech 3 in 2004 and most recently id Tech 4 in 2011 (including the updated version from the Doom 3: BFG Edition in 2012) before Carmack left id in 2013. id Tech 4 was released as free software, even amongst patent concerns from Creative Labs over Carmack's reverse, while the original Doom source release shipped without music due to complications with the Cygnus Studios developed DMX library (which lead to the Linux version