# Id Tech 3

id Tech 3, popularly known as the Quake III Arena engine, is a game engine developed by id Software for its 1999 game Quake III Arena. It has subsequently been used in numerous games. Commercially, id Tech 3 competed with early versions of the Unreal Engine; both were widely licensed. Originally proprietary, it is now open-source software.
id Tech 3 is based on the earlier id Tech 2, with a large amount of the code rewritten. id Tech 4 was derived from id Tech 3, as was Infinity Ward's IW engine, used in Call of Duty 2 onward.
At QuakeCon 2005, John Carmack announced that the id Tech 3 source code would be released under the GNU General Public License v2.0 or later, and it was released on August 19, 2005. It was originally distributed via FTP, and later moved to GitHub.

## Features
### Graphics

Unlike most other game engines released at the time—including its primary competitor, the Unreal Engine—id Tech 3 requires an OpenGL-compliant graphics accelerator to run. The engine does not include a software renderer, unlike id Tech 2.
id Tech 3 introduced spline-based curved surfaces in addition to planar volumes.
The graphical technology of the game is based tightly around a shader system, where the appearance of many surfaces can be defined in text files referred to as shader scripts. Shaders are described and rendered as several layers. Each layer contains a texture, a "blend mode" that determines how to superimpose it over the previous layer, and texture orientation modes such as environment mapping, scrolling, and rotation. These features can readily be seen within the game, with many bright and active surfaces in each map and even on character models. The shader system goes beyond visual appearance, defining the contents of volumes (e.g. a water volume is defined by applying a water shader to its surfaces), light emission and which sound to play when a volume is trodden upon. In order to assist calculation of these shaders, id Tech 3 implements a specific fast inverse square root function, which attracted a significant amount of attention in the game development community for its clever use of integer operations.

### Networking

Like id's earlier titles Doom and Quake, Quake III Arena features multiplayer support via features built into its engine. id Tech 3 uses a snapshot system to relay information about game frames to the client over UDP. The server updates object interaction at a fixed rate independent of the rate that clients update the server with their actions, then attempts to send the state of all objects at that moment (the current server frame) to each client. The server attempts to omit as much information as possible about each frame, relaying only differences from the last frame the client confirmed as received (Delta encoding). All data packets are compressed by Huffman coding with static pre-calculated frequency data to reduce bandwidth use even further.
Quake III Arena has an integrated and relatively elaborate cheat-protection system called "pure server". Any client connecting to a pure server automatically has "pure mode" enabled; while pure mode is enabled, only files within data packs can be accessed. Clients are disconnected if their data packs fail one of several integrity checks. The cgame.qvm file, with its high potential for cheat-related modification, is subject to additional integrity checks. Developers must manually deactivate pure server to test maps or mods that are not in data packs using the PK3 file format. Later versions supplemented pure server with PunkBuster support, though all the hooks to it are absent from the source code release because PunkBuster is closed source software and including support for it in the source code release would have caused any redistributors/reusers of the code to violate the GPL.

## ioquake3

Ioquake3 is a game engine project which aims to build upon the id Tech 3 source code release in order to remove bugs, clean up source code and to add more advanced graphical and audio features via SDL and OpenAL. ioquake3 is also intended to act as a clean base package, upon which other projects may be built. The game engine supports Ogg Vorbis format and video capture of demos in .avi format.
The project was started shortly after the source code release with the goal of creating a bug-free, enhanced open source Quake III engine source code distribution upon which new games and projects can be based. In addition, the project aims to provide an improved environment in which Quake III: Arena, the Team Arena expansion pack and all the popular mods can be played. The project added features including builtin VoIP support, Anaglyph stereo rendering (for viewing with 3D glasses), and numerous security fixes.
Ioquake3 is the basis of several game projects based on the id Tech 3 engine, such as OpenArena (mimicking Quake III Arena), Tremulous, Smokin' Guns, Urban Terror, Turtle Arena and World of Padman and game engine projects such as efport (a Star Trek: Voyager – Elite Force Holomatch clone), ioJedi Outcast, ioJedi Academy, ioDoom3, and OpenMoHAA. The engine and its associated games have been included in several Linux and BSD distributions. The cMod engine derived from the earlier Elite Force port was used to package the 20th anniversary freeware release of the game for Windows and Linux.
The source code for the Return to Castle Wolfenstein and Wolfenstein: Enemy Territory engines was released under GNU GPL-3.0-or-later on August 12, 2010. The ioquake3 developers announced the start of other engine projects.
The ioquake3 project has been used academic research such as Stanford University's Center for Computer Research in Music and Acoustics (CCRMA), Notre Dame as the foundation for VR research, and Swinburne University of Technology's Centre for Advanced Internet Architectures. Collaborative efforts from researchers at Carnegie Mellon University and the University of Toronto use ioquake3 as a platform for their published research. Students have used ioquake3 as the basis for advanced graphics work for their theses, such as Stephan Reiter's work which has been noted at the LLVM project due to his synthesis of the ioquake3 engine, ray-tracing rendering technique, and LLVM.
The project has since received forks, such as Quake3e, Spearmint, and vkQuake3.
Other derived engines include the Daemon engine used by Unvanquished, as well as competing source ports like XreaL, Kwaak3 for Android and Quake-3-Android-Port-QIII4A.

## Games

| Year | Title | Developer | Notes |
| 1999 | Quake III Arena | id Software | |
| 2000 | Heavy Metal: F.A.K.K. 2 | Ritual Entertainment | ÜberTools |
| 2000 | Star Trek: Voyager – Elite Force | Raven Software | |
| 2000 | American McGee's Alice | Rogue Entertainment | ÜberTools |
| 2000 | Quake III: Team Arena | id Software | |
| 2001 | Quake III Revolution | Bullfrog Productions | |
| 2001 | James Bond 007: Agent Under Fire | EA Redwood Shores | ÜberTools |
| 2001 | Return to Castle Wolfenstein | Gray Matter Studios (SP) Nerve Software (MP) | |
| 2002 | Medal of Honor: Allied Assault | 2015, Inc. | ÜberTools |
| 2002 | Star Wars Jedi Knight II: Jedi Outcast | Raven Software | |
| 2002 | Soldier of Fortune II: Double Helix | Raven Software | |
| 2002 | Medal of Honor: Allied Assault - Spearhead | EA Los Angeles | ÜberTools |
| 2003 | Wolfenstein: Enemy Territory | Splash Damage | |
| 2003 | Star Trek: Elite Force II | Ritual Entertainment | ÜberTools |
| 2003 | Medal of Honor: Allied Assault - Breakthrough | TKO Software | ÜberTools |
| 2003 | Star Wars Jedi Knight: Jedi Academy | Raven Software | |
| 2003 | Call of Duty | Infinity Ward | ÜberTools |
| 2004 | James Bond 007: Everything or Nothing | EA Redwood Shores | ÜberTools |
| 2004 | Call of Duty: United Offensive | Gray Matter Studios Treyarch | ÜberTools |
| 2004 | Medal of Honor: Pacific Assault | EA Los Angeles | ÜberTools |
| 2008 | Iron Grip: Warlord | ISOTX | |
| 2009 | Dark Salvation | Mangled Eye Studios | |
| 2009 | Call of Duty Classic | Infinity Ward | ÜberTools |
| 2010 | Quake Live | id Software | |
| Cancelled | Severity | Escalation Studios | |
| Cancelled | Trinity: The Shatter Effect | Gray Matter Studios | |