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IDProjectCategoryView StatusDate SubmittedLast Update
0003792Zandronum[All Projects] Bugpublic2020-05-28 22:402026-05-20 09:52
ReporterSoul 
Assigned To 
PriorityhighSeveritymajorReproducibilityalways
StatusconfirmedResolutionopen 
PlatformOSMicrosoft Windows 10OS Version
Product Version3.1-beta 
Target VersionFixed in Version 
Summary0003792: Incorrect hitscan behavior
DescriptionIt is possible to shoot at angles that should not be true in Vanilla settings where freelook is disabled. In the demo provided (see Additional Information), a player's Shotgun shot not only came out at a different angle from where the player's POV was when firing (typical desync behavior), missing the target completely when not supposed to, the pellets also somehow hit the floor instead of the wall in front of them. The player's target was on the same level as them, meaning vertical autoaim was not supposed to activate, and it was impossible for the target to be on the position the pellets hit as there is no lower floor in that spot.
Steps To ReproduceIt appears to be completely random, although it might be easier to reproduce when holding the Fire button upon respawning, assuming this is an extension of a desync bug.

1. zandronum -iwad doom2.wad -file autoaim_glitch_01.wad +map map01
2. "give all" in the console.
3. Select the shotgun and fire without altering your aim. The puffs should hit the floor nearer the player compared to vanilla Doom.
Additional InformationTimestamp of this occurrence:
- Skip the demo to the Eyedea map;
- After the duel begins, immediately after my first death, as I respawn on a Shotgun, this happens.

Images:
Frame when I shoot -'https://i.imgur.com/NDEx1uz.png [^]'
Frame where the bullet puffs are visible to me -'https://i.imgur.com/eTqi6WZ.png [^]'
Where the pellets hit (spectator view) -'https://i.imgur.com/7uDyoOB.png [^]'
Attached Files7z file icon 2020.05.06_01.54.59_doom2.duel2020zf.newtextcolours_260pk3.cld.7z [^] (1,510,182 bytes) 2020-05-28 22:40
png file icon autoaim_comparison.png [^] (371,063 bytes) 2026-05-20 09:36
? file icon autoaim_glitch_01.wad [^] (8,734 bytes) 2026-05-20 09:36

- Relationships

-  Notes
User avatar (0024754)
unknownna (updater)
2026-05-20 09:36

 I decided to investigate this, and can confirm that it's actually a vanilla Doom quirk with the autoaim on that particular map at that particular spot.

The glitch also occurs in Odamex 12.1.0 and Chocolate Doom, though the puffs spawn a bit further back on those ports, since they share the vanilla Doom tracer behavior.

Zandronum (and ZDaemon) uses the ZDoom behavior, that has been present since at least version 1.22, so it's an ancient ZDoom quirk.
Nonetheless, the ZDoom behavior differs from the vanilla Doom one, and setting "compat_autoaim" to 1 doesn't make it work like vanilla Doom, since that compatflag only changes how many aim tracers there are.

I'm not sure whether it makes much of a difference in practice, but fixing this would require someone to bring back the vanilla tracer behavior, and probably lump it together with "compat_autoaim 1", especially since later GZDoom versions change the autoaim behavior even further from GZDoom 1.8.6, the version that Zandronum currently is based on.

I made an example wad based on the offending map that 100% allows you to demonstrate the difference between Zandronum and vanilla Doom.
Load up the map and use the "give all" cheat on Zandronum, or "idkfa" with the menu open in Chocolate Doom prior to firing at the voodoo doll.
Select the shotgun, and make sure your aim doesn't deviate from the spawn angle so you don't accidentally hit the voodoo doll and throw it off.
The puffs will always spawn a bit further back in Chocolate Doom and Odamex compared to Zandronum.

1. zandronum -iwad doom2.wad -file autoaim_glitch_01.wad +map map01
2. "give all" in the console.
3. Select the shotgun and fire without altering your aim. The puffs should hit the floor nearer the player compared to vanilla Doom.

See the attached screenshot for an additional comparison of the ports.

Quote from Soul
It appears to be completely random, although it might be easier to reproduce when holding the Fire button upon respawning, assuming this is an extension of a desync bug.


With the steps above, it's 100% reproducible, but the weapon desync that occurred after respawns with non-DECORATE weapons has been fixed now since 3.2 in 0001116.

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- Issue History
Date Modified Username Field Change
2020-05-28 22:40 Soul New Issue
2020-05-28 22:40 Soul File Added: 2020.05.06_01.54.59_doom2.duel2020zf.newtextcolours_260pk3.cld.7z
2026-05-20 09:36 unknownna File Added: autoaim_comparison.png
2026-05-20 09:36 unknownna File Added: autoaim_glitch_01.wad
2026-05-20 09:36 unknownna Note Added: 0024754
2026-05-20 09:36 unknownna Status new => confirmed
2026-05-20 09:37 unknownna Steps to Reproduce Updated View Revisions
2026-05-20 09:52 unknownna Reproducibility random => always




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