Engine bug

From DoomWiki.org

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

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[edit]

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

  • Canonicity — 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 binaries or source code. A bug is disputed if it can be argued to be a harmless and possibly intentional feature.
  • Cause — 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 linedefs (with orphaned tags or incorrectly placed textures) or sectors, can also induce various strange behaviors.
    • The Doom engine includes few safeguards against overflow conditions.
    • Line-of-sight calculations, rendering algorithms, and the BSP tree are also susceptible to 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 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.
  • Fixed in 1.9 — Some bugs appear only in versions of Doom prior to v1.9.
  • 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 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 speedruns or deathmatches).
Phenomenon Canonicity Cause Fatal? Fixed in
1.9?
Workaround? Loophole?
(0,0) respawning bug Undisputed Algorithm N N N Y
Absurd texture name in error message Undisputed Algorithm Y* N N N
AASTINKY and AASHITTY Undisputed Algorithm N N N N
All-ghosts effect Undisputed Overflow N* N N N
Arch-Vile fire spawned at the wrong location Undisputed Typo N N N N
Armor percentage rollover Undisputed Static limit N* Y S N
Baron attacks a monster behind him Algorithm N N N N
Barrel explosions which do no damage Undisputed Algorithm N N N N
Barrel suicide Undisputed Algorithm N Y N Y
Blast damage has unlimited vertical range Undisputed Algorithm N N N Y
Blockmap overflow Undisputed Overflow N N N N
Broadcast packet meltdown Verified N* Y N
Bullet puffs do not appear in outdoor areas Algorithm N N N
Chaingun makes two sounds firing single bullet Undisputed Algorithm N N N N
Colormap blink ignores concurrent powerup [1] N N N N
Crushed barrels leave behind a pool of blood Undisputed Algorithm N N Y N
Crushed monsters block player movement Verified Algorithm N Y N N
Demo desyncing caused by bouncing lost souls Undisputed Algorithm N N N N
Demo desyncing caused by menu access Undisputed Algorithm N N N N
Demon speed bug Algorithm Y* N Y
Drawsegs overflow Undisputed Static limit N N S N
Elastic collisions with walls Undisputed Roundoff N N N Y
Fast doors make two closing sounds Undisputed Algorithm N N N N
Fast doors reopening with wrong sound Disputed Algorithm N N N N
Final Doom teleporters do not set Z coordinate Undisputed Algorithm N N N N
Firing frame position not updated when the player dies Algorithm N N N N
Flawed collision detection Undisputed Algorithm N N N
Floors and ceilings moving silently Undisputed N N N Y
Frag count rollover Overflow N N N N
Gamma correction resets palette Undisputed Algorithm N N N Y
Ghost monsters Undisputed Algorithm N N N N
Hall of Mirrors effect (limit) Undisputed Algorithm N N S N
Hall of Mirrors effect (missing texture) Undisputed Linedef N N Y N
Health limited to 199 Algorithm N Y N N
Health percentage hysteresis in sector type 11 Algorithm N N N N
Hitscan attacks hit invisible barriers in large open areas Algorithm N
IDCHOPPERS cheat confers 1 tic of invulnerability Typo N N N
IDCLEV idiosyncrasies N N N N
IDMUS requests invalid music Algorithm Y N N N
Inaccurate trigonometry table Undisputed Algorithm N N N N
Invulnerability colormap bug Disputed Algorithm N N N N
IRQ 2 does not work Verified Y
Items respawn with pickup flag off Verified Algorithm N Y
joyb_speed magic numbers Overflow N Y Y
Kill percentage flag used for -nomonsters and respawning Disputed Algorithm N* N N Y
Linedef type 37 Y N Y N
Linedefs can be activated regardless of player's Z position Undisputed Algorithm N N N Y
Long wall error Undisputed Roundoff N N S N
Lopsided final boss explosions Undisputed Typo N N N N
Lost soul charging backwards Disputed Algorithm N N N Y
Lost soul clipping problems Undisputed Algorithm N Y N N
Lost soul colliding with items Undisputed Algorithm N N N Y
Lost soul limit Undisputed Static limit N N N Y
Lost soul target amnesia Disputed Algorithm N N N N
Lump size limit Static limit N S N
Mancubus fireball clipping Undisputed Algorithm N N N N
Manual doors on 1S lines cause an illegal operation Undisputed Linedef Y* N Y N
Map size limit (blocks) Undisputed Static limit Y N S N
Map size limit (integer overflow) Static limit N N N N
Medusa effect Undisputed Algorithm N* N Y N
Menu error with high mouse sensitivity Undisputed Overflow Y N Y N
Moiré error Undisputed Overflow N* Y S N
Monsters attacking across tall ledges Disputed Algorithm N N N N
Monsters fleeing Disputed Algorithm N N N
Monsters open locked doors Undisputed Roundoff N N N Y
Monsters stuck in doortracks, walls or hanging off lifts Undisputed Algorithm N N N Y
Moving platforms limit Undisputed Linedef Y N S N
Moving platform heights not preserved in saved games Undisputed Algorithm N N N N
Negative vertical offsets are ignored in texture patches Undisputed Algorithm N N N N
Network game crashes with 3 or 4 players Verified Y Y N
Network play locks up when using a sound card Verified Y Y N
Noclip bug Undisputed Overflow N N N Y
Non-Newtonian motion of corpses Disputed Algorithm N N N Y
Numeric overflow crash in tall areas Undisputed Overflow Y* N S N
Ouch face Verified [2] Typo N N N N
Par times hidden in Final Doom after idclev or reload N N N N
Pause bug in menus with scroll bars Undisputed Algorithm N N N N
Phantom fireball explosions Disputed Algorithm N N N
Picked up a medikit that you REALLY need! Undisputed Typo N N N N
Player corpses walking Undisputed Overflow N* N Y N
Player face grins after restoring savefile Disputed Algorithm N N N N
Player starts missing Undisputed Y N Y N
Player stuck on ledge after restoring savefile Undisputed Algorithm N* N N N
Projectiles explode on impact with "sky" Algorithm N N N N
Projectiles triggering linedefs Verified Algorithm N Y N Y
PS/2 mouse bug Verified Y
PWAD size limit Undisputed Algorithm Y N Y N
Quantum lost soul Disputed Algorithm N N N N
Raising sectors change to orphaned sector type Disputed Sector N N Y N
Random sound pitch removed N N N N
Ranged attacks blocked by decorations Disputed Algorithm N N N Y
Recurrent blast damage Undisputed Algorithm N N S Y
Retriggering an open door after loading a savegame causes crash Verified Algorithm Y Y N N
Revenant tracers desync internal demos Undisputed Algorithm N* N N N
Rocket passes through the player who fired it Disputed Algorithm N N N Y
Savegame buffer overflow Undisputed Static limit Y N S N
Savegame slots 5 and 6 corrupt other files Verified N Y N
Screen melt effect during Doom II cast sequence Algorithm N N N N
Secret exit idiosyncrasies Algorithm N N Y N
Secret sectors appear or disappear Algorithm N N S N
Sector type 17 is disabled after loading a saved game Undisputed Algorithm N N N N
Silent BFG trick Undisputed Static limit N N N Y
Single-use line actions can fail Undisputed Algorithm N* N N Y
Skill level cannot be selected in some network games Verified N Y
Sky hack absorbs attacks regardless of height Undisputed Algorithm N N N N
Sky never changes in Doom II Undisputed Algorithm N N N N
Sleeping Sergeant of Doom II MAP02 Undisputed Typo N N N
Slime trails Undisputed Roundoff N N N N
Some game options not preserved in saved games Undisputed Algorithm N N N N
Sound cutoffs Disputed Static limit N N N N
Sound effects behave differently on level 8 Disputed Algorithm N N N N
Sounds changing pitch on slow computers N N
Spawn fog in wrong location Undisputed Typo N N N N
Spawn cubes miss east & west targets Undisputed Algorithm N N Y N
Spawn spots not preserved in saved games Undisputed Algorithm Y* N N Y
Spechits overflow Undisputed Static limit Y N S N
Spider paralysis Undisputed Algorithm N N N Y
Sprites flickering across ledges or lifts Disputed Algorithm N N N N
Stairs create unknown sector types Undisputed Algorithm Y* N N N
Stairs that can be ascended, but not descended Disputed Algorithm N N Y N
Starting on a vertex between visplanes causes illegal memory access Undisputed N N Y N
Status bar face hysteresis Disputed Algorithm N N N N
Straferunning Undisputed Algorithm N N N Y
Switches and lifts deactivated when restoring a saved game Verified Algorithm N Y N N
Tag 666 idiosyncrasies Undisputed Algorithm N N Y N
Tag 667 idiosyncrasies Undisputed Algorithm N* N N N
Targets not preserved in saved games Undisputed Algorithm N N N Y
Turning resolution is lowered when recording demos Undisputed Static limit N N N N
Tutti-frutti effect Undisputed Linedef N N Y N
Venetian blind crash Undisputed Multiple Y N N N
Vertical cutoff of partially invisible sprites Undisputed Static limit N N N N
Visible sprites limit Undisputed Static limit N N S N
Visplane overflow Undisputed Static limit Y N S N
Voodoo doll Undisputed Algorithm N* N Y N
Wallrunning Undisputed Algorithm N N N Y
Weapon sighting is off center N N N N
Wrong sound for exit switches N N N N
Wrong sound origin for button "popouts" Undisputed Algorithm N N N N
Wrong sound origin for switch/button presses Undisputed Algorithm N N N N
Z_Malloc error Verified Y

See also[edit]