View source for Doom engine

{{short description|1993 game engine}}
{{DISPLAYTITLE:''Doom'' engine}}
{{Infobox video game engine
| name = id Tech 1
| logo = 
| screenshot = 
| caption = [[Doom (1993 video game)|Doom]] running on the ''Doom Engine''.
| collapsible = 
| author = 
| developer = [[id Software]] (John Carmack, John Romero, Dave Taylor)
| replaces = [[Wolfenstein 3D engine]]
| replaced_by = [[Quake engine]]
| latest release version = 1.9
| latest release date = {{release date and age|1995|02|01}}
| repo = [https://github.com/id-Software/DOOM github.com/id-Software/DOOM]
| tools = 
| programming language = [[C (programming language)|C]], [[Assembly language]]
| platform = [[MS-DOS]], [[PC-98]], [[Microsoft Windows|Windows]], [[Mac (computer)|Mac]], [[Linux]], [[Android (operating system)|Android]], [[Amiga]], [[NeXTSTEP]], [[NeXT]], [[Atari Jaguar|Jaguar]], [[32X]], [[PlayStation]], [[3DO Interactive Multiplayer|3DO]], [[Nintendo 64]], [[Sega Saturn|Saturn]], [[Game Boy Advance]], [[Nintendo Switch|Switch]], [[BSD]], [[Unix]], others
| discontinued = yes
| license = [[GNU General Public License|GNU GPL-2.0-or-later]]<ref>{{cite web |title=Doom source code, under the GNU GPL |url=https://www.gamers.org/pub/idgames/source/doomsrc.txt |website=gamers.org |archive-url=https://web.archive.org/web/20230531233251/https://www.gamers.org/pub/idgames/source/doomsrc.txt |archive-date=31 May 2023 |url-status=live}}</ref><br />[[List of Doom ports#3DO Interactive Multiplayer|3DO]]: [[MIT license|MIT]]<ref>{{Cite web|url=https://github.com/Olde-Skuul/doom3do/blob/master/LICENSE|title=Doom3do/LICENSE at master · Olde-Skuul/Doom3do|website=[[GitHub]]|date=17 December 2022|access-date=14 February 2019|archive-date=19 February 2022|archive-url=https://web.archive.org/web/20220219155118/https://github.com/Olde-Skuul/doom3do/blob/master/LICENSE|url-status=live}}</ref>
}}

'''id Tech 1''', also known as the '''''Doom'' engine''', is the [[game engine]] used in the [[id Software]] [[video game]]s ''[[Doom (1993 video game)|Doom]]'' and ''[[Doom II: Hell on Earth]]''. It is also used in ''[[Heretic (video game)|Heretic]]'', ''[[Hexen: Beyond Heretic]]'', ''[[Strife (1996 video game)|Strife: Quest for the Sigil]]'', ''[[Doom WAD#Total conversions|Hacx: Twitch 'n Kill]]'', ''[[Freedoom]]'', and other games produced by licensees. It was created by [[John D. Carmack|John Carmack]], with auxiliary functions written by [[Mike Abrash]], [[John Romero]], [[Dave D. Taylor|Dave Taylor]], and Paul Radek. Originally developed on [[NeXT]] computers,<ref>{{Cite web |title=NeXT Computers - Company - Computing History |url=http://www.computinghistory.org.uk/det/927/NeXT-Computers/ |access-date=2022-03-29 |website=www.computinghistory.org.uk |archive-date=2022-03-29 |archive-url=https://web.archive.org/web/20220329152654/http://www.computinghistory.org.uk/det/927/NeXT-Computers/ |url-status=live }}</ref> it was [[porting|ported]] to [[MS-DOS]] and compatible operating systems for ''Doom''<nowiki>'</nowiki>s initial release and was later ported to several [[game console]]s and [[operating system]]s.

The [[source code]] to the [[Linux]] version of ''Doom'' was released to the public under a license that granted rights to non-commercial use on December 23, 1997, followed by the Linux version of ''Doom II'' about a week later on December 29, 1997.<ref>{{cite web|archive-url=https://web.archive.org/web/19980218070336/http://www.pcgamer.com/news/news-1997-12-29.html |url=http://www.pcgamer.com:80/news/news-1997-12-29.html |title=Doom II Source Available |author=Staff |work=[[PC Gamer US]] |date=December 29, 1997 |archive-date=February 18, 1998 |url-status=dead |access-date=November 20, 2019 |df=mdy-all }}</ref><ref>https://web.archive.org/web/*/ftp://ftp.idsoftware.com/idstuff/source/* {{cite web |url=ftp://ftp.idsoftware.com/idstuff/source/ |archive-url=https://web.archive.org/web/20151202080952/ftp://ftp.idsoftware.com/idstuff/source/ |archive-date=2015-12-02 |url-status=dead |title=FTP link |work=ftp.idsoftware.com }}</ref> The source code was later re-released under the [[GNU General Public License|GNU General Public License v2.0 or later]] on October 3, 1999.<ref>{{Cite web |url=https://www.doomworld.com/idgames/source/doomsrc |title=Doom source code, under the GNU GPL - Doomworld /idgames database frontend |access-date=2021-03-28 |archive-date=2021-03-28 |archive-url=https://web.archive.org/web/20210328161448/https://www.doomworld.com/idgames/source/doomsrc |url-status=live }}</ref><ref>
[http://www.3ddownloads.com/showfile.php3?file_id=7430 The ''Doom'' source code from 3ddownloads.com] {{webarchive |url=https://web.archive.org/web/20040224122359/http://www.3ddownloads.com/showfile.php3?file_id=7430 |date=February 24, 2004 }} - released in 1997, now under the [[GNU GPL]] v2-or-later</ref>
The dozens of unofficial [[Doom source ports|''Doom'' source ports]] that have been created since then allow ''Doom'' to run on previously unsupported operating systems and sometimes radically expand the engine's functionality with new features.

Although the engine renders a 3D space, that space is projected from a two-dimensional [[floor plan]]. The line of sight is always parallel to the floor, walls must be perpendicular to the floors, and it is not possible to create multi-level structures or sloped areas (floors and ceilings with different angles). Despite these limitations, the engine represented a technological leap from id's previous [[Wolfenstein 3D engine|''Wolfenstein 3D'' engine]]. The ''Doom'' engine was later renamed{{Citation needed|date=August 2024|reason=There is no source for 'id Tech 1' being the official name of this engine. The cited Giant Bomb article doesn't say anything about this. id Software's licensing site didn't feature an 'id Tech 1', only id Tech 2. Before the introduction of this brand in 2007, the licensing page only featured the three Quake engines.
https://web.archive.org/web/20070501000000*/http://www.idsoftware.com/business/technology}} to "id Tech 1" in order to categorize it in a list of [[id Tech|id Software's long line of game engines]].<ref>{{cite web |title=id Tech 1 (Concept) |url=http://www.giantbomb.com/id-tech-1/3015-3803/ |website=[[Giant Bomb]] |access-date=2019-02-14 |archive-date=2019-02-15 |archive-url=https://web.archive.org/web/20190215050335/https://www.giantbomb.com/id-tech-1/3015-3803/ |url-status=live }}</ref>

==Game world==
The ''Doom'' engine separates rendering from the rest of the game. The graphics engine runs as fast as possible, but the game world runs at 35 frames per second regardless of the hardware, so multiple players can play against each other using computers of varying performance.<ref name="schuytema199408">{{Cite magazine
 |last=Schuytema
 |first=Paul C.
 |date=August 1994
 |title=The Lighter Side Of Doom
 |url=http://www.cgwmuseum.org/galleries/index.php?year=1994&pub=2&id=121
 |magazine=Computer Gaming World
 |pages=140, 142
 |access-date=2019-02-14
 |archive-date=2018-01-02
 |archive-url=https://web.archive.org/web/20180102213537/http://www.cgwmuseum.org/galleries/index.php?year=1994&pub=2&id=121
 |url-status=live
 }}</ref>

==Level structure==
<div style="float: right; margin: 0 0 1em 1em; padding: 0.5em; background: #fffff4; border: 1px solid #ddddbb; width: 250px;">
A simple setup demonstrating how ''Doom'' represents levels internally
[[Image:Doom-map-format-map.svg|240px|thumb|Map view in editor]]

</div>

Viewed from the top down, all ''Doom'' levels are actually two-dimensional, demonstrating one of the key limitations of the ''Doom'' engine: [[room-over-room]] is not possible. This limitation, however, has a silver lining: a "map mode" can be easily displayed, which represents the walls and the player's position, much like the first image to the right.

===Basic objects===
The base unit is the [[vertex (geometry)|vertex]], which represents a single 2D point. Vertices (or "vertexes" as they are referred to internally) are then joined to form [[line (mathematics)|lines]], known as "linedefs". Each linedef can have either one or two sides, which are known as "sidedefs". Sidedefs are then grouped together to form [[polygon]]s; these are called "sectors". Sectors represent particular areas of the level.

===Sectors===
Each sector contains a number of properties: a floor height, ceiling height, light level, a floor [[Texture mapping|texture]] and a ceiling texture. To have a different light level in a particular area, for example, a new sector must be created for that area with a different light level. One-sided linedefs therefore represent solid walls, while two-sided linedefs represent bridge lines between sectors.

===Sidedefs===
Sidedefs are used to store wall [[Texture mapping|textures]]; these are completely separate from the floor and ceiling textures. Each sidedef can have three textures; these are called the middle, upper and lower textures. In one-sided linedefs, only the middle texture is used for the texture on the wall. In two-sided linedefs, the situation is more complex. The lower and upper textures are used to fill the gaps where adjacent sectors have different floor and ceiling heights: lower textures are used for steps, for example. The sidedefs can have a middle texture as well, although most do not; this is used to make textures hang in mid air. For example, when a transparent bar texture is seen forming a cage, this is an example of a middle texture on a two-sided linedef.

==Binary space partitioning==
''Doom'' makes use of a system known as [[binary space partitioning]] (BSP).<ref name=Engine>{{cite web|last=Abrash|first=Michael|title=Quake's 3-D Engine: The Big Picture|url=http://www.bluesnews.com/abrash/|access-date=22 August 2012}}</ref>  A tool is used to generate the BSP data for a level beforehand. This process can take quite some time for a large level. It is because of this that it is not possible to move the walls in ''Doom''; while doors and lifts move up and down, none of them ever move sideways.

The level is divided up into a [[binary tree]]: each location in the tree is a "node" which represents a particular area of the level (with the root node representing the entire level). At each branch of the tree there is a dividing line which divides the area of the node into two subnodes. At the same time, the dividing line divides linedefs into line segments called "segs".<ref name=bsptree>{{cite web|last=Apted|first=Andrew|title=SPECIFICATION for GL-Nodes|url=http://www.faqs.org/faqs/graphics/bsptree-faq/|access-date=22 August 2012|archive-date=2 September 2012|archive-url=https://web.archive.org/web/20120902064055/http://www.faqs.org/faqs/graphics/bsptree-faq/|url-status=live}}</ref>

At the leaves of the tree are [[convex polygon]]s, where further division of the level is not needed. These convex polygons are referred to as subsectors (or "SSECTORS"), and are bound to a particular sector. Each subsector has a list of segs associated with it.<ref name=Engine />

The BSP system sorts the subsectors into the right order for rendering. The algorithm is fairly simple:

#Start at the root node.
#Draw the child nodes of this node recursively. The child node closest to the camera is drawn first using a [[Scanline algorithm]]. This can be found from looking at which side of the node's dividing line the camera is on.
#When a subsector is reached, draw it.<ref name=EngineReview>{{cite web|last=Sanglard|first=Fabien|title=Doom engine code review|url=http://fabiensanglard.net/doomIphone/doomClassicRenderer.php|access-date=23 August 2012|archive-date=3 September 2012|archive-url=https://web.archive.org/web/20120903074732/http://fabiensanglard.net/doomIphone/doomClassicRenderer.php|url-status=live}}</ref>

The process is complete when the whole column of pixels is filled (i.e., there are no more gaps left). This ordering ensures that no time is used drawing objects that are not visible and as a result maps can become very large without any speed penalty.

==Rendering==
{{unreferenced section|date=January 2012}}
{{Original research section|date=February 2023}}

===Drawing the walls===
[[File:Camera Rotation vs Shearing.gif|thumb|Animated comparison of camera rotation in a true 3D environment, left, vs shearing in a 2.5D environment like ''Doom'', right.]]
All of the walls in ''Doom'' are drawn vertically; it is because of this that it is not possible to properly look up and down. It is possible to perform a form of look up/down via [https://zdoom.org/wiki/Y-shearing "y-shearing"], and many modern ''Doom'' source ports do this, as well as later games that use the engine, such as ''[[Heretic (video game)|Heretic]]''. Essentially this works by moving the horizon line up and down within the screen, in effect providing a "window" on a taller viewable area. By moving the window up and down, it is possible to give the illusion of looking up and down. However, this will distort the view the further up and down the player looks.

The ''Doom'' engine renders the walls as it traverses the BSP tree, drawing subsectors by order of distance from the camera so that the closest segs are drawn first. As the segs are drawn, they are stored in a linked list. This is used to clip other segs rendered later on, reducing overdraw. This is also used later to clip the edges of sprites.

Once the engine reaches a solid (1-sided) wall at a particular x coordinate, no more lines need to be drawn at that area. For clipping the engine stores a "map" of areas of the screen where solid walls have been reached. This allows far away parts of the level which are invisible to the player to be clipped completely.

The ''Doom'' graphic format stores the wall textures as [[row- and column-major order|sets of vertical columns]]; this is useful to the renderer, which essentially renders the walls by drawing many vertical columns of textures.

===Floor and ceiling===
The system for drawing floors and ceilings ("flats") is less elegant {{Says who|date=February 2023}} than that used for the walls. Flats are drawn with a [[flood fill]]-like algorithm. Because of this, if a bad BSP builder is used, it is sometimes possible to get "holes" where the floor or ceiling bleeds down to the edges of the screen, a visual error commonly referred to as a "slime trail".<ref>[https://doomwiki.org/w/index.php?title=Slime_trail&oldid=193418 Slime trail - The Doom Wiki]</ref> This is also the reason why if the player travels outside of the level using the [[Noclip mode|noclip cheat]], the floors and ceilings will appear to stretch out from the level over the empty space.

The floor and ceiling are drawn as "visplanes". These represent horizontal runs of texture, from a floor or ceiling at a particular height, light level and texture (if two adjacent sectors have exactly the same floor, these can get merged into one visplane). Each x position in the visplane has a particular vertical line of texture which is to be drawn.

Because of this limit of drawing one vertical line at each x position, it is sometimes necessary to split visplanes into multiple visplanes. For example, consider viewing a floor with two [[concentric]] squares. The inner square will vertically divide the surrounding floor. In that horizontal range where the inner square is drawn, two visplanes are needed for the surrounding floor.

''Doom'' contained a static limit on the number of visplanes; if exceeded, a "visplane overflow" would occur, causing the game to exit to DOS with one of two errors, "No more visplanes!" or "visplane overflow (128 or higher)". The easiest way to invoke the visplane limit is a large checkerboard floor pattern; this creates a large number of visplanes.

As the segs are rendered, visplanes are also added, extending from the edges of the segs towards the vertical edges of the screen. These extend until they reach existing visplanes. Because of the way this works, the system is dependent on the fact that segs are rendered in order by the overall engine; it is necessary to draw nearer visplanes first, so that they can "cut off" by others further away. If unstopped, the floor or ceiling will "bleed out" to the edges of the screen, as previously described. Eventually, the visplanes form a "map" of particular areas of the screen in which to draw particular textures.

While visplanes are constructed essentially from vertical "strips", the actual low level rendering is performed in the form of horizontal "spans" of texture. After all the visplanes have been constructed, they are converted into spans which are then rendered to the screen. This appears to be a trade off: it is easier to construct visplanes as vertical strips, but because of the nature of how the floor and ceiling textures appear it is easier to draw them as horizontal strips.

===Things (sprites)===
Each sector within the level has a linked list of things stored in that sector. As each sector is drawn the sprites are placed into a list of sprites to be drawn. If not within the field of view these are ignored.

The edges of sprites are clipped by checking the list of segs previously drawn. Sprites in ''Doom'' are stored in the same column based format as the walls are, which again is useful for the renderer. The same functions which are used to draw walls are used to draw sprites as well.

While subsectors are guaranteed to be in order, the sprites within them are not. ''Doom'' stores a list of sprites to be drawn ("vissprites") and sorts the list before rendering. Far away sprites are drawn before close ones. This causes some overdraw but usually this is negligible.

There is a final issue of middle textures on 2-sided lines, used in transparent bars for example. These are mixed in and drawn with the sprites at the end of the rendering process, rather than with the other walls.

== Games using the ''Doom'' engine ==

The ''Doom'' engine achieved most of its fame as a result of powering the classic first person shooter ''[[Doom (1993 video game)|Doom]]'', and it was used in several other games. It is usually considered that the "Big Four" ''Doom'' engine games are ''[[Doom (1993 video game)|Doom]]'', ''[[Heretic (video game)|Heretic]]'', ''[[Hexen: Beyond Heretic]]'', and ''[[Strife (1996 video game)|Strife: Quest for the Sigil]]''.

=== Games built directly on the ''Doom'' engine ===
{| class="wikitable sortable"
!Year
!Title
!Developer
|-
|1993
|''[[Doom (1993 video game)|Doom]]''
| rowspan="2" |[[id Software]]
|-
| rowspan="2" |1994
|''[[Doom II: Hell on Earth]]''
|-
|''[[Heretic (video game)|Heretic]]''
|[[Raven Software]]
|-
| rowspan="1" |1995
|''[[Hexen: Beyond Heretic]]''
|Raven Software
|-
| rowspan="4" |1996
|''[[Final Doom]]''
|[[TeamTNT]]
|-
|''[[Heretic: Shadow of the Serpent Riders]]''
| rowspan="2" |Raven Software
|-
|''[[Hexen: Deathkings of the Dark Citadel]]''
|-
|''[[Strife: Quest for the Sigil]]''
|[[Rogue Entertainment]]
|}

=== Games based on the ''Doom'' or ''Doom II'' code ===
In the 1990s a handful of developers acquired licenses to distribute [[total conversion]]s of ''Doom'', and following the 1997 source code release a number of standalone titles have been produced in the engine, including [[freeware]], [[fangames]] and commercial titles.<ref>{{cite web|url=https://www.rockpapershotgun.com/modder-superior-the-many-free-descendants-of-doom|title=Modder Superior: The many free descendants of Doom|first=Dominic|last=Tarason|date=2019-04-01|access-date=2024-07-14|website=[[Rock Paper Shotgun]]|archive-date=2023-08-06|archive-url=https://web.archive.org/web/20230806004338/https://www.rockpapershotgun.com/modder-superior-the-many-free-descendants-of-doom|url-status=live}}</ref>

{| class="wikitable sortable"
!Year
!Title
!Developer
|-
|rowspan="2'' |1996
|''[[Killing Time (video game)|Killing Time]]'' (PC)
|Logicware
|-
|''[[Chex Quest]]''
|[[Digital Café]]
|-
| rowspan="3" |1997
|''[[Doom 64]]''
|[[Midway Studios San Diego]]
|-
|''[[Chex Quest 2: Flemoids Take Chextropolis]]''
|Digital Café
|-
|''[[Hacx|HacX]]''
|Banjo Software
|-
|2000
|''[[Sonic Robo Blast 2]]''
|Sonic Team Junior
|-
|2003
|''[[Freedoom]]''
|Freedoom Team
|-
| rowspan="3" | 2008
|''[[Chex Quest 3]]''
|Charles Jacobi
|-
|''[[Blasphemer (video game)|Blasphemer]]''
|Blasphemer Team
|-
|''Action Doom 2: Urban Brawl''<ref>{{cite web|url=https://www.tigsource.com/2008/09/01/action-doom-2-urban-brawl/|title=Action Doom 2: Urban Brawl|first=Derek|last=Yu|date=2008-01-09|access-date=2008-01-09|website=tigsource}}</ref>
| Scuba Steve
|-
|2009
|''Harmony''<ref>{{cite web|website=[[Rock Paper Shotgun]]|first=Kieron|last=Gillen|url=https://www.rockpapershotgun.com/harmony-in-my-head-harmony|title=Harmony in My Head: Harmony|date=2009-11-18|access-date=2023-02-22|archive-date=2023-02-23|archive-url=https://web.archive.org/web/20230223050228/https://www.rockpapershotgun.com/harmony-in-my-head-harmony|url-status=live}}</ref>
| Thomas van der Velden 
|-
|2014
|''The Adventures of Square''<ref>{{cite web|website=GamingOnLinux|first=Liam|last=Dawe|url=https://www.gamingonlinux.com/2018/04/the-adventures-of-square-is-mildly-amusing-retro-fps-thats-free-with-a-second-episode-out-now/|title=The Adventures of Square is mildly amusing retro FPS that's free with a second episode out now|date=2018-04-19|access-date=2023-02-19}}</ref>
| BigBrik Games
|-
|2016
|''Blade of Agony''<ref>{{cite web|url=https://www.rockpapershotgun.com/blade-of-agony-doom-wolfenstein-mod|title=Blade Of Agony Is An Incredible 'WolfenDoom' Mod|first=Adam|last=Smith|date=2016-08-03|access-date=2016-08-03|website=rockpapershotgun}}</ref>
| Daniel Gimmer
|-
|2017
| ''Rise of the Wool Ball''<ref>{{cite web|url=https://www.rockpapershotgun.com/rise-of-the-wool-ball-wolfenstein-3d-mod|title=Shadow & Rise Of The Wool Ball turn Wolfenstein cute|first=Dominic|last=Tarason|date=2018-01-07|access-date=2024-07-14|website=[[Rock Paper Shotgun]]|archive-date=2024-07-15|archive-url=https://web.archive.org/web/20240715030544/https://www.rockpapershotgun.com/rise-of-the-wool-ball-wolfenstein-3d-mod|url-status=live}}</ref>
| MSPaintR0cks
|-
|rowspan="4" | 2018
|''REKKR''<ref>{{cite web|url=https://www.vgr.com/doomguy-is-now-some-kind-of-viking-in-the-rekkr-game/|title=Doomguy Is Now Some Kind Of Viking In The Rekkr Game|first=Rania|last=Tsiro|date=2018-07-12|access-date=2024-07-14|website=VGR|archive-date=2024-07-15|archive-url=https://web.archive.org/web/20240715030544/https://www.vgr.com/doomguy-is-now-some-kind-of-viking-in-the-rekkr-game/|url-status=live}}</ref>
|Mockingbird Softworks
|-
|''Annie''<ref>{{cite web|url=https://www.destructoid.com/doom-2-mod-annie-rises-after-12-year-development-period|title=Doom 2 mod Annie rises after 12 year development period|first=Peter|last=Glagowski|date=2018-08-17|access-date=2018-08-17|website=destructoid}}</ref>
|SergeJkn
|-
|''Ashes''<ref>{{cite web|url=https://www.rockpapershotgun.com/ashes-2063-post-apoc-doom-mod-launch|title=Brave a very 80s apocalyptic wasteland in Doom conversion Ashes 2063|first=Dominic|last=Tarason|date=2018-09-24|access-date=2018-09-24|website=rockpapershotgun|archive-date=2021-06-17|archive-url=https://web.archive.org/web/20210617063350/https://www.rockpapershotgun.com/ashes-2063-post-apoc-doom-mod-launch|url-status=live}}</ref>
|Vostyok
|-
|''Total Chaos''<ref>{{cite web|url=https://www.gamingonlinux.com/2018/11/total-chaos-is-an-impressive-and-scary-total-conversion-for-doom-2-making-it-a-survival-horror-experience/|title=Total Chaos is an impressive and scary total conversion for Doom 2 making it a survival horror experience|first=Liam|last=Dawe|date=2018-11-05|access-date=2018-11-05|website=gamingonlinux}}</ref>
|wadaholic
|-
|rowspan="3" | 2019
|''Hocus Pocus Doom''<ref>{{cite web|url=https://www.rockpapershotgun.com/hocus-pocus-doom-turns-apogees-90s-platformer-into-a-fps|title=Hocus Pocus Doom drags Apogee's DOS platformer into the third dimension|first=Dominic|last=Tarason|date=2019-01-14|access-date=2019-01-14|website=rockpapershotgun}}</ref>
|Ravage
|-
|''Hedon''<ref>{{cite web|url=https://www.vgr.com/hedon-pc-game-review/|title=Hedon – PC Game Review|first=Alyxx|last=Digre|date=2019-05-16|access-date=2024-07-14|website=VGR|archive-date=2024-07-15|archive-url=https://web.archive.org/web/20240715030544/https://www.vgr.com/hedon-pc-game-review/|url-status=live}}</ref>
|Zan_HedonDev
|-
|''Shrine''<ref>{{cite web|url=https://www.pcgamer.com/butcher-some-cosmic-horrors-in-doom-2-mod-shrine/|title=Butcher some cosmic horrors in Doom 2 mod Shrine|first=Jonathan|last=Bolding|date=2019-12-27|access-date=2019-12-27|website=pcgamesn}}</ref>
|Scumhead
|-
|2020
|''[[Alien Breed 3D|Project Osiris]]''<ref>{{cite web|url=https://www.dsogaming.com/news/someone-has-created-a-alien-breed-3d-remake-in-gzdoom-and-you-can-download-it-right-now/|title=Someone has created an Alien Breed 3D Remake in GZDoom, and you can download it right now|date=2020-03-16|access-date=2024-06-22|first=John|last=Papadopoulos|website=DSOGaming}}</ref>
| ArcturusDeluxe 
|-
|rowspan="2" | 2021
|''Castlevania: Simon’s Destiny''<ref>{{cite web|url=https://www.rockpapershotgun.com/castlevania-simons-destiny-doom-mod|title=Castlevania: Simon's Destiny is a treat of a Doom mod|first=Dominic|last=Tarason|date=2021-06-27|access-date=2021-06-27|website=rockpapershotgun}}</ref>
|batandy
|-
|''Vomitoreum''<ref>{{cite web|url=https://techraptor.net/gaming/reviews/vomitoreum-review|title=Vomitoreum Review|date=2021-08-11|accessdate=2024-07-14|first=Peter|last=Glagowski|website=Tech Raptor|archive-date=2024-07-15|archive-url=https://web.archive.org/web/20240715030544/https://techraptor.net/gaming/reviews/vomitoreum-review|url-status=live}}</ref> 
| Scumhead
|-
| rowspan="4" | 2022
|''Hands Of Necromancy''<ref>{{cite web|url=https://www.gamingonlinux.com/2022/06/gzdoom-powered-dark-fantasy-fps-hands-of-necromancy-is-out-now/|title=GZDoom powered dark-fantasy FPS 'Hands of Necromancy' is out now|first=Liam|last=Dawe|date=2022-05-22|access-date=2024-07-15|website=GamingOnLinux}}</ref>
| HON Team
|-
|''CountryCide''<ref>{{cite web|url=https://www.gamepressure.com/newsroom/countrycide-new-version-of-stunning-dark-mod-for-doom-2/z242e7|title=CountryCide - New Version of Stunning Dark Mod for Doom 2|first=Adrian|last=Werner|date=2022-04-22|access-date=2022-04-22|website=gamepressure}}</ref>
| TrenchWork
|-
|''Project Absentia''<ref>{{cite web|url=https://hellforgestudios.com/games/project-absentia/|title=Project Absentia|date=30 October 2022 }}</ref>
| Waffle Iron Studios
|-
|''I Am Sakuya: Touhou FPS Game''{{citation needed|date=September 2024}}
|Sigyaad Team
|-
|rowspan="3" | 2023
|''Supplice''<ref>{{cite web|url=https://www.pcgamer.com/supplice-is-a-new-retro-fps-made-by-doom-modders-and-it-really-feels-like-old-school-doom/|title=Supplice is a new retro-FPS made by Doom modders, and it really feels like old-school Doom|first=Andy|last=Chalk|date=2023-08-05|access-date=2023-06-05|website=PCGamer}}</ref>
| Mekworx
|-
|''Venturous''<ref>{{cite web|url=https://kotaku.com/doom-mod-ventrous-indy-indiana-jones-download-pc-1850887493|title=New Doom Mod Is Basically A Badass Indiana Jones Game|first=Zack|last=Zwiezen|date=2023-09-29|access-date=2023-09-29|website=kotaku}}</ref>
|PixelFox
|-
|''Apocalyptic Vibes''<ref>{{cite web|url=https://indie-hive.com/apocalyptic-vibes/|title=Apocalyptic Vibes – An Immersive Journey Through a Faded-out, Post-Nuclear Earth!|first=Tamaster|last=Tamaster|date=2023-03-21|access-date=2023-03-21|website=indie-hive}}</ref>
|Amanito Computing
|-
|rowspan="4" | 2024
|''Hands of Necromancy 2''<ref>{{cite web|url=https://www.pcgamesn.com/hands-of-necromancy-2/boomer-shooter-out-now|title=New retro FPS Hands of Necromancy 2 looks to Heretic for inspiration|first=Alex|last=McHugh|date=2024-09-17|access-date=2024-09-17|website=pcgamesn}}</ref>
| HON Team
|-
|''Beyond Sunset''<ref>{{cite web|url=https://www.pcgamer.com/retro-fps-beyond-sunset-is-a-precision-crafted-cyberpunk-potpourri-of-all-the-great-megawads-that-came-before-it/|title=Retro FPS Beyond Sunset is a precision-crafted cyberpunk potpourri of all the great megawads that came before it|first=Mova|last=Smith|date=2023-12-14|access-date=2023-12-14|website=pcgamer}}</ref>
| Metacorp / Vaporware
|-
|''Selaco''<ref>{{cite web|url=https://kotaku.com/selaco-gzdoom-engine-fps-steam-review-early-access-1851513067|title=New FPS Built Using Doom Tech Is Better Than Most AAA Shooters|first=Zack|last=Zwiezen|date=2024-05-31|access-date=2024-07-14|website=[[Kotaku]]|archive-date=2024-07-15|archive-url=https://web.archive.org/web/20240715030544/https://kotaku.com/selaco-gzdoom-engine-fps-steam-review-early-access-1851513067|url-status=live}}</ref>
| Altered Orbit Studios
|-
|''Borrowhelen''<ref>{{cite web|url=https://kotaku.com/games/borrowhelen/gallery|title=Borrowhelen Screenshots and Videos - Kotaku|first=Kotaku|last=Kotaky|date=2024-11-25|access-date=2024-11-25|website=[[Kotaku]]}}</ref>
| 4-Cube Games
|-
|rowspan="2" | 2025
|''Mala Petaka''<ref>{{cite web|url=https://www.pcgamer.com/games/fps/this-2025-shooter-made-in-a-decades-old-doom-engine-is-gorgeous-fun-and-tough-as-nails/|title=This 2025 shooter made in a decades-old Doom engine is gorgeous, fun, and tough as nails|first=Joshua|last=Wolens|date=2025-10-06|access-date=2025-10-06|website=pcgamer}}</ref>
| Sanditio Bayu, Hellforge Studios
|-
|''Mohrta''<ref>{{cite web|url=https://www.pcgamer.com/games/fps/one-of-my-most-anticipated-shooters-which-looks-like-demons-souls-in-the-doom-engine-finally-has-a-release-date-right-around-the-corner/|title=One of my most anticipated shooters, which looks like Demon's Souls in the Doom engine, finally has a release date right around the corner|first= Ted|last=Litchfield|date=2025-10-14|access-date=2025-10-03|website=pcgamer}}</ref>
| Scumhead, Osiol
|}

== See also ==
{{Portal|Free and open-source software|Video games}}
*[[List of game engines]]
*[[First-person shooter engine]]
*[[id Tech]]
*[[Build (game engine)]]
*[[Quake engine|''Quake'' engine]]
*[[Quake (series)|''Quake'' (series)]]
*[[List of first-person shooter engines]]

==Notes==
* [https://glbsp.sourceforge.net/specs.php GL nodes specification]
* [https://web.archive.org/web/20070305204905/http://www.doomworld.com/classicdoom/utils/editors.php Utilities to edit Doom and Doom2]
* [http://fabiensanglard.net/doomIphone/doomClassicRenderer.php Doom engine code review] by Fabien Sanglard

==References==
{{Reflist}}

==External links==
* [https://doomwiki.org/wiki/Doom_engine Doom engine] on [https://doomwiki.org Doom Wiki]
* [https://doomwiki.org/wiki/Doom_rendering_engine Doom rendering engine] on [https://doomwiki.org Doom Wiki]
* [http://www.uvlist.net/groups/info/doomengine Doom engine full games list]
* [https://github.com/id-Software/DOOM Source code of the Doom engine]

{{Id Software}}
{{DOOMgames}}
{{Video game engines}}

[[Category:1993 software]]
[[Category:Doom (franchise)]]
[[Category:Formerly proprietary software]]
[[Category:Game engines for Linux]]
[[Category:Id Tech]]