# Quake II engine

The Quake II engine (id Tech 2.5), is a game engine developed by id Software for use in their 1997 first-person shooter Quake II. It is the successor to the Quake engine. Since its release, the Quake II engine has been licensed for use in several other games.
One of the engine's most notable features was out-of-the-box support for hardware-accelerated graphics, specifically OpenGL, along with the traditional software renderer. Another interesting feature was the subdivision of some of the components into dynamic-link libraries. This allowed both software and OpenGL renderers, which were selected by loading and unloading separate libraries. Libraries were also used for the game logic, with consequences including:
* Since they were compiled for specific platforms, instead of an interpreter, they could run faster than Quake's solution, which was to run the game logic (QuakeC) in a limited interpreter.
* id could release the source code to allow modifications while keeping the remainder of the engine proprietary.
The level format, as with previous id Software engines, used binary space partitioning. The level environments were lit using lightmaps, a method in which light data for each surface is precalculated (this time, via a radiosity method) and stored as an image, which is then used to determine the lighting intensity each 3D model should receive, but not its direction.
id Software released the source code on December 22, 2001, under the terms of the GNU General Public License v2.0 or later.

## Games using the Quake II engine
### Games using a proprietary license

| Year | Title | Developer |
| 1997 | Quake II | id Software |
| 1998 | Quake II Mission Pack: The Reckoning | Xatrix Entertainment |
| 1998 | Quake II Mission Pack: Ground Zero | Rogue Entertainment |
| 1998 | Zaero (unofficial expansion for Quake II) | Team Evolve |
| 1998 | Juggernaut: The New Story (unofficial expansion for Quake II) | HeadGames Publishing |
| 1998 | Heretic II | Raven Software |
| 1998 | SiN | Ritual Entertainment |
| 1999 | SiN: Wages of Sin | 2015, Inc. |
| 1999 | Kingpin: Life of Crime | Xatrix Entertainment |
| 2000 | Soldier of Fortune | Raven Software |
| 2000 | Daikatana | Ion Storm |
| 2001 | Anachronox | Ion Storm |

### Games based on the GPL source release

| Year | Title | Developer |
| 2000 | D-Day: Normandy | D-Day: Normandy Team |
| 2003 | UFO: Alien Invasion | UFO: Alien Invasion Team |
| 2008 | Gravity Bone | Blendo Games |
| 2012 | Warsow | Warsow Team |
| 2012 | Thirty Flights of Loving | Blendo Games |
| 2017 | Alien Arena: Warriors of Mars | COR Entertainment, LLC |
| 2017 | Quetoo | Quetoo Team |
| 2019 | Warfork | Warfork Team |

## Ports

* Jake2 – a Java port of the Quake II engine's GPL release. It has since been used by Sun as an example of Java Web Start capabilities for games distribution over the Internet. In 2006, it was used to experiment playing 3D games with eye tracking. The performance of Jake2 is on par with the original C version.
* Quake2Forge – one of the earliest community produced source ports.
* Quake2xp – a port of Quake II to modern operating systems.
* KMQuake2 – an upgraded engine for Quake II.
* Quake2maX – OpenGL focused source port.
* Quake 2 Evolved – early graphically enhanced game engine.
* Quetoo (formerly Quake2World) – multiplayer focused port derived from Quake2Forge.
* Berserker@Quake2 – graphically enhanced Quake II port.
* Yamagi Quake II – a port of Quake II to modern systems which aims to preserve the original gameplay.
* vkQuake2 – the original Quake II engine with additional Vulkan renderer created by Krzysztof Kondrak, a programmer from Poland. It was originally released in December 2018 under the GPLv2.
* CRX Engine – custom version for CodeRED: Alien Arena.
* Qfusion – a modification of the GPL version of the engine. The engine was used in the 2012 game Warsow.
* Q2Pro – a mutliplayer oriented port, which was also used as the basis for Quake II RTX.
* R1Q2 – another multiplayer focused port.
* DirectQII – DirectX oriented source port.
* Fruitz of Dojo – a source port aimed at Mac OS X.
* Q2DOS – a backport of the game to MS-DOS.