Simulation false positive while sneaking between walls and fences

[rayanbzd]

Describe the false positive and how to replicate it

To reproduce, simply put fences and walls every other block, then sneak and walk between it.
Video:

Enregistrer.l.ecran.2024-08-21.a.21.14.10.mov

This might be because the player can actually fit almost pixel perfect between a wall and a fence (see screenshot below)

So when the player sneak and walk between, maybe simulation think the player should fall in the little gap while he's not ?

Grim Log

https://paste.grim.ac/15mkupb

Server version

Paper 1.21.1 (build 35)

Client version

Vanilla 1.21

Plugins

LuckPerms, GrimAC, WorldEdit, WorldGuard, CoreProtect, and personal plugins that doesn't interfer with packets/movements.
Also reproduced on a localhost server hosted on my computer with only GrimAC on it.

[rayanbzd]

will be fixed in 2047

This is an issue section, not circus of sarcasm.
Fix it yourself if you think it's easy to.

[SamB440]

Can you test if this happens on older client versions? Like 1.19.4. I am wondering if Mojang has changed the sneaking calculation

[rayanbzd]

Can you test if this happens on older client versions? Like 1.19.4. I am wondering if Mojang has changed the sneaking calculation

Just tested in 1.19.4, same problem. The false is triggered when i'm exactly in the middle gap where it's supposed to be possible to fall in the gap between the wall and the fence.

[SamB440]

Most likely related to #858

[SamB440]

Interestingly it doesn't happen on my custom 1:1 simulator, I will have to see what Grim is doing wrong at some point

[rayanbzd]

Just tested in old version of minecraft (1.12.2) and doesn't happen.

[rayanbzd]

Interestingly it doesn't happen on my custom 1:1 simulator, I will have to see what Grim is doing wrong at some point

Is your custom simulator opensource ?