Editing Quake III Arena (section)

===Game engine===
{{Main|id Tech 3}}
[[Image:Quake III Arena q3dm0.png|thumb|right|A mirror reflects Sarge and the ''Quake III'' logo in the opening scene of the first level, Q3DM0.]]
The ''id Tech 3'' engine is the name given to the engine that was developed for ''Quake III Arena''. Unlike most other games released at the time, ''Quake III Arena'' requires an [[OpenGL]]-compliant [[Graphics processing unit|graphics accelerator]] to run. The game does not include a [[Software rendering|software]] or [[Direct3D]] renderer.

The graphic 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". ''Quake 3'' also introduced spline-based curved surfaces in addition to planar volumes, which are responsible for many of the surfaces present within the game.<ref name="shader5">{{cite web |url = http://www.qeradiant.com/manual/Q3AShader_Manual/ch05/pg5_1.htm |archive-url = https://web.archive.org/web/20010223094944/http://www.qeradiant.com/manual/Q3AShader_Manual/ch05/pg5_1.htm |url-status = dead |archive-date = 2001-02-23 |title = Quake III Arena Shader Manual |access-date = 2006-10-01 |page = 5 |author = Paul Jaquays, Brian Hook }}</ref> ''Quake 3'' also provided support for models animated using [[morph target animation|vertex animation]] with attachment tags (known as the [[MD3 (file format)|.md3]] format), allowing models to maintain separate torso and leg animations and hold weapons. ''Quake 3'' is one of the first games where the third-person model is able to look up and down and around as the head, torso and legs are separate. Other visual features include [[Volumetric lighting|volumetric fog]], mirrors, portals, decals, and wave-form vertex distortion.

For networking, id Tech 3 uses a "snapshot" system to relay information about game "frames" to the client over [[User Datagram Protocol|UDP]]. 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]]).<ref name="network">{{cite web |url = http://trac.bookofhook.com/bookofhook/trac.cgi/wiki/Quake3Networking |title = Book of Hook: The Quake3 Networking Model |access-date = 2006-10-01 |archive-url = https://web.archive.org/web/20061027183301/http://trac.bookofhook.com/bookofhook/trac.cgi/wiki/Quake3Networking |archive-date = 2006-10-27 |url-status = dead }}</ref> ''id Tech 3'' uses a [[virtual machine]] to control object behavior on the server, effects and prediction on the client and the user interface. This presents many advantages as mod authors do not need to worry about crashing the entire game with bad code, clients could show more advanced effects and game menus than was possible in ''[[Quake II]]'' and the user interface for mods was entirely customizable. Unless operations which require a specific [[endianness]] are used, a QVM file will run the same on any platform supported by ''Quake III Arena.'' The engine also contains bytecode compilers for the [[X86 architecture|x86]] and [[PowerPC]] architectures, executing QVM instructions via an [[interpreter (computing)|interpreter]].

''Quake III Arena'' features an advanced [[Artificial intelligence|AI]] with five difficulty levels which can accommodate both a beginner and an advanced player, though they usually do not pose a challenge to high-tier or competitive players. Each bot has its own, often humorous, 'personality', expressed as scripted lines that are triggered to simulate real player chat. If the player types certain phrases, the bots may respond: for example, typing "You bore me" might cause a bot to reply "You should have been here 3 hours ago!". Each bot has a number of alternative lines to reduce the repetition of bot chatter. The Gladiator bots from ''Quake II'' were ported to ''Quake III Arena'' and incorporated into the game by their creator - Jan Paul van Waveren, aka Mr. Elusive.<ref>[http://members.cox.net/randar/review.html http://members.cox.net/randar/review.html] {{webarchive |url=https://web.archive.org/web/20070926222311/http://members.cox.net/randar/review.html |date=September 26, 2007 }} ''Members.cox.net''</ref><ref>{{cite web |url=http://www.kbs.twi.tudelft.nl/docs/MSc/2001/Waveren_Jean-Paul_van/thesis.pdf |title=The Quake III Bot, J.P. van Waveren |access-date=2011-08-17 |archive-date=2005-03-05 |archive-url=https://web.archive.org/web/20050305151021/http://www.kbs.twi.tudelft.nl/docs/MSc/2001/Waveren_Jean-Paul_van/thesis.pdf |url-status=live }}</ref> Bot chat lines were written by [[R. A. Salvatore]], Seven Swords and Steve Winter.<ref name="salvatore">{{cite web |title=Quake III Arena Credits |url=http://www.gamefaqs.com/computer/doswin/data/192047.html |work=[[GameFAQs]] |access-date=2007-05-16 |archive-date=2005-02-07 |archive-url=https://web.archive.org/web/20050207195502/http://www.gamefaqs.com/computer/doswin/data/192047.html |url-status=live }}</ref> Xaero, the hardest opponent in the game, was based on the Gladiator bot Zero. The bot Hunter appears on magazine covers in the later id game ''[[Doom 3]]''.

On August 19, 2005, id Software released the complete source code for ''Quake III Arena'' under the [[GNU General Public License|GNU General Public License v2.0 or later]],<ref>{{cite web |url=http://games.slashdot.org/article.pl?sid=05/08/20/1329236&tid=112|title=Quake 3: Arena Source GPL'ed) |work=[[Slashdot]] |access-date=2008-06-23 |date=2005-08-20}}</ref> as they have for most of their prior engines. As before, the ''engine'', but not the content such as textures and models, was released, so that anyone who wishes to build the game from source will still need an original copy of the game to play it as intended.