Editing Doom source code

The '''Doom source code''' was released [[Timeline#1997|December 23, 1997]], initially under a not-for-profit license. Later, permission was granted to re-release the source code under the GNU [[Wikipedia:GPL|GPL]] on [[Timeline#1999|October 3, 1999]].

Before release, the source code was tidied up by [[Bernd Kreimeier]]; the source release includes a changelog of his contributions. Several documentation files are also included. The original plan for the source code release involved a book Kreimeier was to write on the Doom engine; however, due to Doom's decreasing relevance in the gaming community, it was eventually judged not to be a marketable idea, and the project was abandoned. The source code was then released to the public.

Because of legal issues regarding the [[DMX]] [[sound]] library developed by [[Paul Radek]] which was used for Doom, the release was of the source code to the [[Wikipedia:Linux|Linux]] port of Doom. Despite this, within several months, several ports had been made back to DOS. As a result, many [[source ports]] exist.

== Source code structure ==

The source code can be divided into sections. Files and functions within the source code have one- or two-letter prefixes to denote their subsystem.

; AM_*
:  [[Automap]] code
; D_*
:  Initialisation/general code
; F_*
:  "Finale" (end of game) and "[[screen melt]]" code.
; G_*
:  Main game loop/control
; HU_*
:  [[Heads-up display]]
; I_*
:  System-specific code
; M_*
:  Miscellaneous (includes the menu)
; P_*
:  Game logic/behaviour
; R_*
:  [[Doom rendering engine|Rendering engine]]
; S_*
:  [[Sound]] code
; ST_*
:  [[Status bar]]
; V_*
: General graphic rendering
; WI_*
:  End-of level "intermission" screen
; W_*
:  [[WAD]] file loading
; Z_*
:  [[Zone memory|Zone memory allocation system]]

The following are common prefixes for functions, although they do not denote a particular subsystem, and there are no files with these prefixes:

; A_*
:  Action functions invoked in sprite movement frames (these are the functions used in [[Dehacked]] "code pointers")
; PIT_*
: Callback functions passed to P_BlockThingsIterator (see p_maputl.c)
; T_*
: "[[Thinker]]" functions set to be called each clock [[tic]] for some purpose (eg, moving platforms or flickering lights)

A detailed list of files and their purposes can be found in [[Doom source code files]].

==Doom Classic==
''[[Doom 3: BFG Edition]]'' incorporates the "Doom Classic" port allowing to play [[The Ultimate Doom]] and [[Doom II]] on 32- and 64-bit Windows, on the [[Xbox 360]] and on the [[PlayStation 3]]. There are a few changes done to the source code and packaging here. Notably:
* Bugs introduced in the LinuxDoom code by Bernd Kreimeier's cleanup and changes are absent
* [[MUS|MUS2MIDI]] and [[TiMidity]] are incorporated for MIDI playback, instead of using [[DMX]]
* A few [[static limits]] have been raised, notably [[visplane]]s and [[drawseg]]s to accommodate for [[No Rest for the Living]]'s levels
* Several #defines have been moved out of their original files and into either Precompiled.h or defs.h (both new files)
* The [[Master Levels]] and No Rest for the Living are handled as mission packs like [[TNT: Evilution]] and [[Plutonia]]
* The French language file is still present but emptied, French is removed from the language_t enum
* The code is available under the GPLv3 or later

Note: this should not be confused with the iOS port also named [[Doom Classic (iOS)|Doom Classic]].

==See also==
* [[Heretic source code]]
* [[Hexen source code]]
* [[Doom 3 source code]]

== External links ==
* [https://www.doomworld.com/10years/ports/ports01_1.php Doomworld - 10 years of Doom] - some history of the Doom source release.
* {{idgames|id=8802|title=Doom source code}} (Original [[Licences#Source code release|DOOM Source Licensed]] version)
* {{idgames|id=14576|title=Doom source code}} (Revised [[Licences#GNU_General_Public_License_.28GPL.29|GPL]] version)
* [https://github.com/id-Software/DOOM GitHub repository for Doom]
* [https://github.com/id-Software/DOOM-3-BFG/tree/master/doomclassic GitHub repository for Doom Classic]

[[Category:Doom engine]]
[[Category:Code]]