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Id Tech 4

id Tech 4
Developer(s)id Software
Written inC++[1]
PlatformMicrosoft Windows, OS X, Linux, PlayStation 3, PlayStation 4, Xbox, Xbox 360, Xbox One, Nintendo Switch, Nvidia Shield[2]
Predecessorid Tech 3
Successorid Tech 5
LicenseGNU GPL-3.0-or-later Edit this on Wikidata

id Tech 4, popularly known as the Doom 3 engine, is a game engine developed by id Software and first used in the video game Doom 3. The engine was designed by John Carmack, who also created previous game engines, such as those for Doom and Quake, which are widely recognized as significant advances in the field. This OpenGL-based game engine has also been used in Quake 4, Prey, Enemy Territory: Quake Wars, Wolfenstein, and Brink. id Tech 4 is licensed under the terms of the GNU General Public License v3.0 or later.


id Tech 4 began as an enhancement to id Tech 3. During development, it was initially just a complete rewrite of the engine's renderer, while still retaining other subsystems, such as file access, and memory management. The decision to switch from C to the C++ programming language necessitated a restructuring and rewrite of the rest of the engine; today, while id Tech 4 contains code from id Tech 3, much of it has been rewritten.[3]

At the QuakeCon 2007, John Carmack, the lead graphics engine developer at id, said to LinuxGames: "I mean, I won't commit to a date, but the Doom 3 stuff will be open source". And like its predecessors, John Carmack has said that id Tech 4 will be released as open-source.[4]

At the QuakeCon 2009, Carmack said that he planned to petition ZeniMax Media to release the id Tech 4 source upon the release of Rage.[5] As part of his keynote for QuakeCon 2011, he confirmed that the source code to Doom 3 would be out by the end of the year, after the release of Rage.[6]

On November 16, 2011, Carmack announced on Twitter that he's writing new code for Doom 3's open source release, because "lawyers are still skittish about the patent issue around 'Carmack's reverse'".[7] This refers to an implementation of stencil buffered shadow volume algorithms.

On November 22, 2011, Carmack released the Doom 3 source code under GNU GPL-3.0-or-later on GitHub.[8] The source does not include any of the 'Carmack's Reverse' code. According to Carmack, minor tweaks were made to the code to avoid any infringement.[9] Since then, several open-source projects have been released, such as dhewm3, Dante, and RBDOOM-3-BFG.[10][11][12]


The original requirement of id Tech 4 was that it needed a high-end graphics processing unit (GPU) with fully programmable vertex and pixel shaders, such as the Nvidia GeForce 3 or ATI Radeon 8500, with at least 64 MB of VRAM. By E3 2002, the recommended GPU was "100% DirectX 9.0b compatible", such as the Radeon 9700 with 128 MB of VRAM. While the Radeon 9700's DirectX 9.0 features are not necessary to render the game, its advanced architecture, 256-bit memory bus, and efficiency were needed to run Doom 3 at high detail and playable speed.[13] The "Ultra" graphics mode included in Doom 3 would not even run on high end graphics cards in 2004, as the engine required at least 512 MB of video memory to display properly and at playable speeds.[14]

id Tech 4 resulted in the obsolescence of DirectX 7 graphics chips such as the widespread GeForce 2 and Radeon 7200, as well as older chipsets such as RIVA TNT2 and Rage 128, and software rendering (with an integrated Intel GMA). Until the advent of id Tech 4, a powerful CPU was able to somewhat compensate for an older video card. While John Carmack initially warned gamers not to purchase the GeForce 4 MX[15] (which casual consumers often confused with the DirectX 8 capable GeForce 4 Ti, though it was at best an improved GeForce 2)[citation needed], its somewhat widespread adoption compelled id Software to add it to the list of supported cards. There have been cases of enthusiasts forcing Doom 3 to run on unsupported graphics chips, such as the long obsolete Voodoo 2, but these are unable to render the per-pixel lighting and bump mapping.[16]


The shadowing effects of the unified lighting and shadowing engine are shown on the face and body of the zombies in this screenshot of Doom 3.


Id Tech 4 added several new graphical features absent in its predecessor, id Tech 3. These included normal mapping and specular highlighting. More features were added in the development of successive games.

The primary innovation of id Tech 4 was its use of entirely dynamic per-pixel lighting, whereas previously, 3D engines had relied primarily on pre-calculated per-vertex lighting or lightmaps and Gouraud shading. While dynamic effects had been available before (such as dynamic moving lights), this effect merely changed the brightness of the vertices of the polygon, with the pixel's colors simply being interpolated between the three vertex colors of its polygon.

This fully realtime approach used in Doom 3, combined with the use of shadow volumes permitted more realistic lighting and shadows[17] than in the previous generation of id's engines. The method used to create the shadow volumes is the subject of a patent by Creative, which Creative granted id permission to use in the Doom 3 engine, in exchange for supporting Creative's EAX advanced sound technologies.[18]

The models used in id Tech 4 engine games are animated using skeletal animation. The engine can blend multiple animations together, to produce a skin that moves correctly for those animations. Because this is CPU intensive, id did some work optimizing this by using Intel's Streaming SIMD Extensions (SSE).[19]

MegaTexture rendering technology

The original version of the id Tech 4 engine was designed for somewhat dark environments and was criticized for its perceived inability to handle extremely large daytime outdoor areas. The MegaTexture technology (a form of clipmapping) tackled this issue. By painting a single massive texture (32,768×32,768 pixels, though it has been extended to larger dimensions in recent versions of the MegaTexture technology) covering the entire polygon map and highly detailed terrain, the desired effects can be achieved. The MegaTexture can also store physical information about the terrain such as the amount of traction in certain areas or indicate what sound effect should be played when walking over specific parts of the map. i.e. walking on rock will sound different from walking on grass.[20] The first game utilizing MegaTexture is Enemy Territory: Quake Wars, based on the Tech 4 engine. All id Tech 5 and id Tech 6 games use MegaTexture, with the exception of The Evil Within, which uses a new renderer.[21][22] Brink, which uses a heavily modified version of id Tech 4 also uses virtual texturing.[23][24] While the implementation is different from MegaTexture, it was inspired by it.[25][26]

Rendering techniques used in id Tech 4


id Tech 4 has a comprehensive scripting language that can be used when creating mods, and is used in Doom 3 to control monsters, weapons, and map events. This scripting language is similar to C++.[28]

In addition to the main scripting language, idTech 4 also has another scripting language that is used for GUIs—both the menus and HUD, and also for GUIs embedded into the game world.[29] These in-game GUIs are sufficiently powerful that you can, for example, run another game such as the original Doom within the game-world.[30]

Despite this additional level of scripting, it is also possible to create mods using C++ to build native code.[31]


As a result of the agreement with Creative regarding the patent on shadow volumes, the id Tech 4 engine supports OpenAL, including the Creative Technology specific EAX extensions. The work to include OpenAL support was done by Creative Technology, not by id themselves.[32]


The engine uses a traditional client–server model. Initially it was planned to have a peer-to-peer networking model.[33] This part of the engine works in a fundamentally similar way to the id Tech 3 equivalent; however, id Tech 4 exposes a lot more of the network protocol to mod developers.[31]

Although Doom 3 only supports 4 players (and 8 in the Resurrection of Evil expansion pack), the id Tech 4 engine can be used with more players than this, with Quake 4 and Enemy Territory: Quake Wars both supporting significantly more players.

Games using id Tech 4

Prey utilized a modified version of id Tech 4 that allowed for effects such as portals, variable gravity, and wall walking.

Compared to the preceding and widely used id Tech 3 (Quake III Arena engine) and id Tech 2 (Quake II engine), id Tech 4 has had less success in licensing to third parties.[34] This is especially apparent in comparison to its closest contemporaries, Unreal Engine 2 (2002) and Unreal Engine 3 (2006) from Epic Games.[35] id Software was unwilling to license their newest engine before its "parent game" Doom 3 was completed. However, the unexpectedly long development time going into Doom 3 from 2002-04 meant that they could not put up competition to Epic Games's Unreal Engine 2 during that period. Many who licensed Unreal Engine 2 were thus able to make the switch to Unreal Engine 3 more easily.

While id Tech 4 had taken a new direction with its dynamic per-pixel lighting, this unconventional feature had steeper hardware requirements and was initially only useful in "spooky games" (until the MegaTexture addition), whereas an increasing number of developers preferred conventional engines that could render large outdoor areas. Also notable was id Tech 4's relative lack of downward scalability compared to competing FPS engines; id Tech 4 generally required a DirectX 8.0 compliant GPU such as a GeForce 3. The rival Source engine[a] could still run on the older widespread DirectX 7 GPUs, albeit without the use of shaders.

Games using a proprietary license

Year Title Developer
2004 Doom 3 id Software
2005 Doom 3: Resurrection of Evil Nerve Software
Quake 4 Raven Software
2006 Prey Human Head Studios
2007 Enemy Territory: Quake Wars Splash Damage
2009 Wolfenstein Raven Software
2011 Brink Splash Damage
2012 Doom 3: BFG Edition id Software
Cancelled Quake 4: Awakening Ritual Entertainment
SiN 2[36]
Prey 2 Human Head Studios

Games using an open-source license

Year Title Developer
2013 The Dark Mod[b]
2016 Quadrilateral Cowboy Blendo Games[39]
TBA Skin Deep Blendo Games

See also


  1. ^ Developed from the GoldSrc engine, itself derived from id Tech 2
  2. ^ Began as an effort to recreate Thief: The Dark Project within Doom 3.[37] It became a standalone game once the Doom 3 source code was released.[38]


  1. ^ "id Tech 4 Source Code". GitHub. March 30, 2020. Archived from the original on April 18, 2019. Retrieved September 11, 2015.
  2. ^ "3D Engine: id Tech 4". Archived from the original on January 28, 2012. Retrieved September 24, 2008.
  3. ^ "Q&A with John Carmack, E3 2002". Archived from the original on September 29, 2009.
  4. ^ Carmack, John (August 7, 2007). "I mean I won't commit to a date, but theDoom 3 stuff will be open source". Archived from the original on October 3, 2008.
  5. ^ "The John Carmack Keynote: Liveblogging QuakeCon". August 13, 2009. Archived from the original on August 14, 2009. Retrieved August 14, 2009.
  6. ^ "Id Software will release the Doom 3 source code". The Inquirer. August 5, 2011. Archived from the original on August 7, 2011. Retrieved August 23, 2015.{{cite web}}: CS1 maint: unfit URL (link)
  7. ^ "John Carmack's Twitter status update". November 16, 2011. Archived from the original on August 26, 2021. Retrieved November 18, 2011.
  8. ^ "Doom 3 Source on GitHub". GitHub. November 22, 2011. Archived from the original on July 21, 2013. Retrieved November 22, 2011.
  9. ^ "John Carmack tweets about code infringement work around". November 17, 2011. Archived from the original on May 16, 2017. Retrieved November 22, 2011.
  10. ^ Larabel, Michael (November 20, 2012). "One Year Later, Open-Source Doom 3 Is Moving Slowly". Phoronix. Retrieved April 29, 2024.
  11. ^ Larabel, Michael (December 19, 2012). "Open-Source Doom 3 BFG Ported To Linux". Phoronix. Retrieved April 29, 2024.
  12. ^ Papadopoulos, John (December 17, 2018). "Final version of Doom 3 source port, dhewm3, available for download, supports 4K, OpenAL and more". DSO Gaming. Retrieved July 14, 2024.
  13. ^ "ATI's Radeon 9700 Takes Performance Lead". Archived from the original on September 21, 2009. Retrieved September 25, 2012.
  14. ^ Hargosh, Todd. "Doom is a boon". Game Industry News. Archived from the original on July 27, 2011. Retrieved June 11, 2011.
  15. ^ ".plan File for John Carmack - Blue's News". Archived from the original on March 3, 2016. Retrieved May 25, 2016.
  16. ^ "Doom3 + Voodoo2_Patch_v1_0". Archived from the original on December 5, 2008. Retrieved September 25, 2012.
  17. ^ "Doom 3". Pricenfees. March 2, 2005. Archived from the original on August 13, 2018. Retrieved May 25, 2016.
  18. ^ "John Carmack: "This sucks."". Ars Technica. July 28, 2004. Archived from the original on January 26, 2012. Retrieved May 25, 2016.
  19. ^ "Optimizing the Rendering Pipeline of Animated Models Using the Intel Streaming SIMD Extensions". Archived from the original on June 24, 2016. Retrieved May 25, 2016.
  20. ^ "GameSpy: Enemy Territory: Quake Wars - Page 1". Archived from the original on August 13, 2018. Retrieved May 25, 2016.
  21. ^ "John Carmack on Twitter". Twitter. Archived from the original on November 14, 2019. Retrieved May 25, 2016.
  22. ^ "John Carmack on Twitter". Twitter. Archived from the original on January 19, 2015. Retrieved May 25, 2016.
  23. ^ "BRINK: Multi-core support and better scaling on the PC". July 29, 2009. Archived from the original on September 13, 2011. Retrieved May 25, 2016.
  24. ^ "Archived copy" (PDF). Archived from the original (PDF) on August 9, 2014. Retrieved May 25, 2016.{{cite web}}: CS1 maint: archived copy as title (link)
  25. ^ "Sparse Virtual Textures". Archived from the original on March 23, 2012. Retrieved May 25, 2016.
  26. ^ "Brink technical analysis". Archived from the original on March 27, 2016. Retrieved May 25, 2016.
  27. ^ "DOOM Eternal Benchmarked at 8K - Not Even The Devil Can Run This". Tweatwon. March 30, 2020. Retrieved November 6, 2023.
  28. ^ "id.sdk [Scripts]". Archived from the original on December 10, 2015. Retrieved May 25, 2016.
  29. ^ "id.sdk [GUIs]". Archived from the original on August 11, 2016. Retrieved May 25, 2016.
  30. ^ "Fully Interactive Surfaces". Archived from the original on April 9, 2016. Retrieved May 25, 2016.
  31. ^ a b "id.sdk [The Code]". Archived from the original on March 7, 2016. Retrieved May 25, 2016.
  32. ^ "How the latest Sound Blaster X-Fi technology was utilized in QUAKE 4". Archived from the original on August 4, 2012. Retrieved September 25, 2012.
  33. ^ "Doom 3 multiplayer networking info". Archived from the original on August 31, 2011.
  34. ^ "id Tech 4 (Concept) - Giant Bomb". Archived from the original on December 1, 2013. Retrieved November 26, 2013.
  35. ^ "id Tech 5". Eurogamer. August 9, 2007. Archived from the original on March 4, 2016. Retrieved September 25, 2012.
  36. ^ "3D Realms releases video of their cancelled prototypes including SiN 2 and Bombshell FPS". Archived from the original on December 3, 2021. Retrieved April 8, 2020.
  37. ^ "Outta Dunwall: Thief Remake The Dark Mod Updates". Rock Paper Shotgun. October 22, 2012. Archived from the original on September 24, 2015. Retrieved August 25, 2015.
  38. ^ "The Dark Mod". October 13, 2011. Archived from the original on April 27, 2021. Retrieved September 11, 2015.
  39. ^ Campbell, Colin (February 4, 2013). "What the Hell is Quadrilateral Cowboy?". IGN. Archived from the original on February 7, 2013. Retrieved February 7, 2013.
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