Editing Engine bug

A [[Doom]] '''engine bug''' is a limitation or an oddity present in the [[Doom engine]]. For errors in [[Levels|map]] design, even those related to a specific item below, see the article about that map.

This article uses the version 1.9 [[DOOM2.EXE]] DOS version as the base version. Older versions, the source release, Final Doom and The Ultimate Doom have some minor changes, tweaks and different bugs.

Note that playing with a [[source port]] may, while removing some or even the majority of the bugs listed below, introduce other bugs which are not listed here (although details may be present in the article about the source port in question).

=== Key ===

This table classifies anomalies in a very broad way; see the individual articles for details.

* '''{{wp|Canon (fiction)|Canonicity}}''' &mdash; A bug is ''verified'' only when a current or former [[id Software]] programmer has called it a bug in a public medium.  An unverified bug may still be ''undisputed'' if it is generally accepted as an error or issue by the fan community under a consensus involving thorough playtesting and research on the corresponding phenomenon and any associated {{wp|Executable|binaries}} or [[Doom source code|source code]]. A bug is ''disputed'' if it can be argued to be a harmless and possibly intentional feature.

* '''Cause''' &mdash; The general category of underlying problem:
** Most bugs are due to ''algorithms'' which fail to account for all possible inputs, apply conditional statements in an illogical sequence, or have unforeseen consequences in particular game situations.
*** A few of these arise from simple ''typos'' in the source code.
** Improperly constructed ''[[linedef]]s'' (with orphaned [[tag]]s or incorrectly placed [[texture]]s) or ''[[sector]]s'', can also induce various strange behaviors.
** The Doom engine includes few safeguards against {{wp|Integer overflow|''overflow'' conditions}}.
** Line-of-sight calculations, [[Doom rendering engine|rendering]] algorithms, and the [[Doom rendering engine#Node building|BSP tree]] are also susceptible to {{wp|Floating point#Accuracy problems|''roundoff'' errors}}.
** The engine imposes a number of ''[[static limits]]'' on [[Thing]] placement and map construction, which sometimes fix one problem by creating another.

* '''Fatal''' bugs are those where the engine crashes (often with the [[Venetian blind crash|Venetian blind]] effect) or else exits the game in a controlled fashion, usually with an [[error message]].  '''Y*''' means that termination is possible, but not inevitable.  '''N*''' means that the program keeps running, but that rendering or character behavior may be sufficiently compromised that meaningful gameplay becomes impossible.

* A bug has a '''workaround''' if it can be avoided by ''reasonable'' compromises in map design, such as when matching every linedef tag to at least one [[sector]], but not when removing [[Invulnerability|invulnerabilities]] from every level containing a sky texture, or also by convenient precautions and other measures taken by the program user, such as when increasing the mouse sensitivity through the configuration file directly, instead of using the menu. '''S''' means that the bug can be avoided only by making one's map smaller or less complex.

* A bug is a '''loophole''' if it can be abused to the player's advantage (especially during [[speedrun]]s or [[deathmatch]]es).

=== Bugs present in Doom II version 1.9 for DOS ===

{| {{prettySortable}}
!Phenomenon
!Canonicity
!Cause
!Fatal?
!Workaround?
!Loophole?
|-
| [[(0,0) respawning bug]]
| Undisputed
| Algorithm
! N
! N
! Y
|-
| [[1% damage bug]]
| 
| Algorithm
! N
! N
! N
|-
| [[Absurd texture name in error message]]
| Undisputed
| Algorithm
! Y*
! N
! N
|-
| [[AASTINKY|AASTINKY and AASHITTY]]
| Undisputed
| Algorithm
! N
! N
! N
|-
| [[All-ghosts effect]]
| Undisputed
| Overflow
! N*
! N
! Y
|-
| [[Anomalous angry face behavior]]
| 
| Algorithm
! N
! N
! N
|-
| [[Arch-vile fire spawned at the wrong location]]
| Undisputed
| Typo
! N
! N
! N
|-
| [[Baron attacks a monster behind him]]
| 
| Algorithm
! N
! N
! N
|-
| [[Barrel explosions which do no damage]]
| Undisputed
| Algorithm
! N
! N
! N
|-
| [[Blast damage has unlimited vertical range]]
| Undisputed
| Algorithm
! N
! N
! Y
|-
| [[Blockmap overflow]]
| Undisputed
| Overflow
! N
! S
! N
|-
| [[Boss level ending not triggered if every player is dead]]
| Undisputed
| Algorithm
! N*
! N
! N
|-
| [[Bullet puffs do not appear in outdoor areas]]
| 
| Algorithm
! N
! N
! 
|-
| [[Chaingun makes two sounds firing single bullet]]
| Undisputed
| Algorithm
! N
! N
! N
|-
| [[Chainsaw negates projectile impact thrust]]
| Undisputed
| Algorithm
! N
! N
! Y*
|-
| [[Colormap blink ignores concurrent powerup]] {{dwforumsp|id=1019768|title=}}
| 
| 
! N
! N
! N
|-
| [[Crash when accessing Read This!]] {{dwforums|id=73271|title=}}
| Undisputed
|
! Y
! N
! N
|-
| [[Barrel#Notes|Crushed barrels leave behind a pool of blood]]
| Undisputed
| Algorithm
! N
! Y
! N
|-
| [[Demo desyncing caused by bouncing lost souls]]
| Undisputed
| Algorithm
! N
! N
! N
|-
| [[Demo desyncing caused by menu access]]
| Undisputed
| Algorithm
! N
! N
! N
|-
| [[Demon speed bug]]
| 
| Algorithm
! Y*
! 
! Y
|-
| [[Doom II monster exclusion bug]]
| Undisputed
| Algorithm
! Y*
! Y
! N
|-
| [[Seg#Drawsegs overflow|Drawsegs overflow]]
| Undisputed
| Static&nbsp;limit
! N
! S
! N
|-
| [[Elastic collisions with walls]]
| Undisputed
| Roundoff
! N
! N
! Y
|-
| [[Fast doors make two closing sounds]]
| Undisputed
| Algorithm
! N
! N
! N
|-
| [[Fast doors reopening with wrong sound]]
| Disputed
| Algorithm
! N
! N
! N
|-
| [[Final Doom teleporters do not set Z coordinate]]
| Undisputed
| Algorithm
! N
! N
! N
|-
| [[Firing frame position not updated when the player dies]]
| 
| Algorithm
! N
! N
! N
|-
| [[Flawed collision detection]]
| Undisputed
| Algorithm
! N
! N
! 
|-
| [[Floors and ceilings moving silently]]
| Undisputed
| 
! N
! N
! Y
|-
| [[Frag count rollover]]
| 
| Overflow
! N
! N
! N
|-
| [[Gamma correction resets palette]]
| Undisputed
| Algorithm
! N
! N
! Y
|-
| [[Ghost monsters]]
| Undisputed
| Algorithm
! N
! N
! N
|-
| [[GUS instrument mappings bug]]
| Undisputed
| Algorithm
! N
! Y
! N
|-
| [[Static_limits#Drawsegs|Hall of Mirrors effect (limit)]]
| Undisputed
| Algorithm
! N
! S
! N
|-
| [[Hall of Mirrors effect|Hall of Mirrors effect (missing texture)]]
| Undisputed
| Linedef
! N
! Y
! N
|-
| [[Health percentage hysteresis in sector type 11]]
| 
| Algorithm
! N
! N
! N
|-
| [[Hitscan attacks hit invisible barriers in large open areas]]
| 
| Algorithm
! N
! 
! 
|-
| [[Chainsaw#Notes|IDCHOPPERS cheat confers 1 tic of invulnerability]]
| 
| Typo
! N
! N
! 
|-
| [[IDCLEV idiosyncrasies]]
| 
| 
! N
! N
! N
|-
| [[IDMUS requests invalid music]]
| 
| Algorithm
! Y
! N
! N
|-
| [[Inaccurate trigonometry table]]
| Undisputed
| Algorithm
! N
! N
! N
|-
| [[Invulnerability colormap bug]]
| Disputed
| Algorithm
! N
! N
! N
|-
| [[Configuration file#Additional settings|joyb_speed magic numbers]]
| 
| Overflow
! N
! Y
! Y
|-
| [[Key pickup resets palette]]
| Undisputed
| Algorithm
! N
! N
! N
|-
| [[Kill percentage flag used for -nomonsters and respawning]]
| Disputed
| Algorithm
! N*
! N
! Y
|-
| [[Linedef type 37]]
| 
| 
! Y
! Y
! N
|-
| [[Linedefs can be activated regardless of player's Z position]]
| Undisputed
| Algorithm
! N
! N
! Y
|-
| [[Long wall error]]
| Undisputed
| Roundoff
! N
! S
! N
|-
| [[Lopsided final boss explosions]]
| Undisputed
| Typo
! N
! N
! N
|-
| [[Lost soul charging backwards]]
| Disputed
| Algorithm
! N
! N
! Y
|-
| [[Lost soul clipping problems]]
| Undisputed
| Algorithm
! N
! N
! N
|-
| [[Lost soul colliding with items]]
| Undisputed
| Algorithm
! N
! N
! Y
|-
| [[Lost soul limit]]
| Undisputed
| Static limit
! N
! N
! Y
|-
| [[Lost soul target amnesia]]
| Disputed
| Algorithm
! N
! N
! N
|-
| [[Lump size limit]]
| 
| Static limit
! 
! S
! N
|-
| [[Mancubus fireball clipping]]
| Undisputed
| Algorithm
! N
! N
! N
|-
| [[Manual doors on 1S lines cause an illegal operation]]
| Undisputed
| Linedef
! Y*
! Y
! N
|-
| [[Map size limit (blocks)]]
| Undisputed
| Static limit
! Y
! S
! N
|-
| [[Map size limit (integer overflow)]]
| 
| Static limit
! N
! N
! N
|-
| [[Medusa effect]]
| Undisputed
| Algorithm
! N*
! Y
! N
|-
| [[Menu error with high mouse sensitivity]]
| Undisputed
| Overflow
! Y
! Y
! N
|-
| [[Monsters attacking across tall ledges]]
| Disputed
| Algorithm
! N
! N
! N
|-
| [[Monsters fleeing]]
| Disputed
| Algorithm
! N
! N
! 
|-
| [[Monsters may target players without ever seeing or hearing them]]
| Disputed
| Algorithm
! N
! N
! N
|-
| [[Monsters open locked doors]]
| Undisputed
| Roundoff
! N
! N
! Y
|-
| [[Monsters stuck in doortracks, walls or hanging off lifts]]
| Undisputed
| Algorithm
! N
! N
! Y
|-
| [[Moving platforms limit]]
| Undisputed
| Linedef
! Y
! S
! N
|-
| [[Moving platform heights not preserved in saved games]]
| Undisputed
| Algorithm
! N
! N
! N
|-
| [[Noclip bug]]
| Undisputed
| Overflow
! N
! N
! Y
|-
| [[Non-Newtonian motion of corpses]]
| Disputed
| Algorithm
! N
! N
! Y
|-
| [[Numeric overflow crash in tall areas]]
| Undisputed
| Overflow
! Y*
! S
! N
|-
| [[Ouch face]]
| Verified [https://web.archive.org/web/20100920220554/http://rome.ro/smf/index.php/topic,1514.msg31763.html#msg31763]
| Typo
! N
! N
! N
|-
| [[Par times hidden in Final Doom after idclev or reload]]
| 
| 
! N
! N
! N
|-
| [[Partial invisibility effect#Animation remains still|Partial invisibility's fuzz effect stays still]]
| 
| Algorithm
! N
! N
! N
|-
| [[Partial invisibility effect#Stippling effect|Partial invisibility stippling algorithm]]
| Disputed
| Algorithm
! N
! N
! N
|-
| [[Pause bug in menus with scroll bars]]
| Undisputed 
| Algorithm
! N
! N
! N
|-
| [[Phantom fireball explosions]]
| Disputed
| Algorithm
! N
! 
! N
|-
| [[Picked up a medikit that you REALLY need!]]
| Undisputed
| Typo
! N
! N
! N
|-
| [[Player corpses walking]]
| Undisputed
| Overflow
! N*
! Y
! N
|-
| [[Player face grins after restoring savefile]]
| Disputed
| Algorithm
! N
! N
! N
|-
| [[Player starts missing]]
| Undisputed
| 
! Y
! Y
! N
|-
| [[Player stuck on ledge after restoring savefile]]
| Undisputed
| Algorithm
! N*
! N
! N
|-
| [[Projectiles explode on impact with "sky"]]
| 
| Algorithm
! N
! N
! N
|-
| [[PWAD size limit]]
| Undisputed
| Algorithm
!Y
!Y
!N
|-
| [[Quantum lost soul]]
| Disputed
| Algorithm
!N
!N
!N
|-
| [[Raising sectors change to orphaned sector type]]
| Disputed
| Sector
!N
!Y
!N
|-
| [[Random sound pitch removed]]
| 
| 
!N
!N
!N
|-
| [[Ranged attacks blocked by decorations]]
| Disputed
| Algorithm
! N
! N
! Y
|-
| [[Blast damage#Non-reentrancy|Recurrent blast damage]]
| Undisputed
| Algorithm
! N
! S
! Y
|-
| [[Revenant tracers desync internal demos]]
| Undisputed
| Algorithm
! N*
! N
! N
|-
| [[Rocket passes through the player who fired it]]
| Disputed
| Algorithm
! N
! N
! Y
|-
| [[Savegame buffer overflow]]
| Undisputed
| Static limit
! Y
! S
! N
|-
| [[Screen melt effect during Doom II cast sequence]]
| 
| Algorithm
! N
! N
! N
|-
| [[Secret level|Secret exit idiosyncrasies]]
| 
| Algorithm
! N
! Y
! N
|-
| [[Secret#Bugs|Secret sectors appear or disappear]]
| 
| Algorithm
! N
! S
! N
|-
| [[Secret#Bugs|Secret sectors have no geometry]]
| 
| Algorithm
! N
! Y
! N
|-
|[[Sector type 17 is disabled after loading a saved game]]
| Undisputed
| Algorithm
! N
! N
! N
|-
|[[Shotgun sprite wraps vertically in Final Doom]]
|
| Algorithm
! N
! Y
! N
|-
| [[Silent BFG|Silent BFG trick]]
| Undisputed
| Static limit
! N
! N
! Y
|-
| [[Single-use line actions can fail]]
| Undisputed
| Algorithm
! N*
! N
! Y
|-
| [[Sky hack absorbs attacks regardless of height]]
| Undisputed
| Algorithm
! N
! N
! N
|-
| [[Sky never changes in Doom II]]
| Undisputed
| Algorithm
! N
! N
! N
|-
| [[Sleeping shotgun guy in MAP02 (Doom II)]]
| Undisputed
| Typo
! N
! N
! 
|-
| [[Slime trail]]s
| Undisputed
| Roundoff
! N
! N
! N
|-
| [[Some Doom II-specific projectiles triggering linedefs]]
| Verified
| Algorithm
! N
! N
! Y
|-
| [[Some game options not preserved in saved games]]
| Undisputed
| Algorithm
! N
! N
! N
|-
| [[Sound cutoffs]]
| Disputed
| Static limit
! N
! N
! N
|-
| [[Sound effects behave differently on level 8]]
| Disputed
| Algorithm
! N
! N
! N
|-
| [[Sounds changing pitch on slow computers]]
| 
| 
! N
! N
! 
|-
| [[Spawn cubes miss east and west targets]]
| Undisputed
| Algorithm
! N
! Y
! N
|-
| [[Spawn fog in wrong location]]
| Undisputed
| Typo
! N
! N
! N
|-
| [[Spawn spots not preserved in saved games]]
| Undisputed
| Algorithm
! Y*
! N
! Y
|-
| [[Spechits overflow]]
| Undisputed
| Static limit
! Y
! S
! N
|-
| [[Spider paralysis]]
| Undisputed
| Algorithm
! N
! N
! Y
|-
| [[Sprites flickering across ledges or lifts]]
| Disputed
| Algorithm
! N
! N
! N
|-
| [[Sprites improperly clipped]]
| 
| Algorithm
! N
! N
! N
|-
| [[Stairs create unknown sector types]]
| Undisputed
| Algorithm
! Y*
! N
! N
|-
| [[Stairs that can be ascended, but not descended]]
| Disputed
| Algorithm
! N
! Y
! N
|-
| [[Starting on a vertex between visplanes causes illegal memory access]]
| Undisputed
| 
! N
! Y
! N
|-
| [[Status bar face hysteresis]]
| Disputed
| Algorithm
! N
! N
! N
|-
| [[Straferunning]]
| Undisputed
| Algorithm
! N
! N
! Y
|-
| [[Tag 666#Difference in behaviour between Doom1 and Ultimate Doom|Tag 666 idiosyncrasies]]
| Undisputed
| Algorithm
! N
! Y
! N
|-
| [[Tag 667#Bugs|Tag 667 idiosyncrasies]]
| Undisputed
| Algorithm
! N*
! N
! N
|-
| [[Targets not preserved in saved games]]
| Undisputed
| Algorithm
! N
! N
! Y
|-
| [[Things snap up to ledges when sectors move]]
| Undisputed
| Algorithm
! N
! Y
! Y
|-
| [[Turning resolution is lowered when recording demos]]
| Undisputed
| Static&nbsp;limit
! N
! N
! N
|-
| [[Tutti-frutti effect]]
| Undisputed
| Linedef
! N
! Y
! N
|-
| [[Unused frames and obstacle sprite]] {{dwforumsp|id=225726|title=}}
| 
| 
! N
! Y
! N
|-
| [[Venetian blind crash]]
| Undisputed
| Multiple
! Y
! N
! N
|-
| [[Partial invisibility effect#Vertical cutoff|Vertical cutoff of partially invisible sprites]]
| Undisputed
| Static limit
! N
! N
! N
|-
| [[Vertical offsets are ignored in texture patches]]
| Undisputed
| Algorithm
! N
! N
! N
|-
| [[Visible sprites limit]]
| Undisputed
| Static&nbsp;limit
! N
! S
! N
|-
| [[Visplane overflow]]
| Undisputed
| Static&nbsp;limit
! Y
! S
! N
|-
| [[Voodoo doll]]
| Undisputed
| Algorithm
! N*
! Y
! N
|-
| [[Wallrunning]]
| Undisputed
| Algorithm
! N
! N
! Y
|-
| [[Weapon pickup message not displayed in multiplayer]]
| 
| Algorithm
! N
! N
! N
|-
| [[Weapon sighting is off center]]
| 
| 
! N
! N
! N
|-
| [[Wrong sound for exit switches]]
| 
| 
! N
! N
! N
|-
| [[Wrong sound origin for button "popouts"]]
| Undisputed
| Algorithm
! N
! N
! N
|-
| [[Wrong sound origin for switch/button presses]]
| Undisputed
| Algorithm
! N
! N
! N
|-
| [[Z_Malloc error]]
| Verified
| Algorithm
! Y
!
! N
|-
|}

=== Bugs present in versions prior to Doom II version 1.9 for DOS ===
{| {{prettySortable}}
!Phenomenon
!Canonicity
!Cause
!Fatal?
!Fixed in<br> version
!Workaround?
!Loophole?
|-
| [[Armor percentage rollover]]
| Undisputed
| Static&nbsp;limit
! N*
! 1.25?
! S
! N
|-
| [[Barrel suicide]]
| Undisputed
| Algorithm
! N
! 1.5?
! N
! Y
|-
| [[Broadcast packet meltdown]]
| Verified
| 
! N*
! 1.2
! 
! N
|-
| [[Crushed monsters block player movement]]
| Verified
| Algorithm
! N
! 
! N
! N
|-
| [[Health limited to 199]]
|
| Algorithm
! N
! 1.25?
! N
! N
|-
| [[IRQ 2 does not work]]
| Verified
| 
! 
! 1.2
! 
! 
|-
| [[Items respawn with pickup flag off]]
| Verified
| Algorithm
! N
!
! 
! 
|-
| [[Moiré error]]
| Undisputed
| Overflow
! N*
! 1.4
! S
! N
|-
| [[Network game crashes with 3 or 4 players]]
| Verified
| 
! Y
! 
! 
! N
|-
| [[Network play locks up when using a sound card]]
| Verified
| 
! Y
! 1.2
! 
! N
|-
| [[Projectiles present in The Ultimate Doom triggering linedefs]]
| Verified
| Algorithm
! N
! 1.4
! N
! Y
|-
| [[PS/2 mouse bug]]
| Verified
| 
! 
! 1.666
! 
! 
|-
| [[Retriggering an open door after loading a savegame causes crash]]
| Verified
| Algorithm
! Y
! 1.2
! N
! N
|-
| [[Savegame slots 5 and 6 corrupt other files]]
| Verified
| 
! N
! 1.2
! 
! N
|-
| [[Skill level cannot be selected in some network games]]
| Verified
| 
! N
! 
! 
! 
|-
| [[Switches and lifts deactivated when restoring a saved game]]
| Verified
| Algorithm
! N
! 
! N
! N
|-
|}

== See also ==

* [[Doom change log]]
* [[Doom source code oddities]]
* [[Static limits]]
* [[Engine bugs in Heretic]]
* [[Engine bugs in Hexen]]
* [[Engine bugs in Strife]]

[[Category:Errors and bugs|*]]
[[Category:Doom engine]]
[[Category:Lists]]