Fast-move Rubber-banding Regression

[Warr1024]

Minetest version

Minetest 5.8.0-dev-6106e4e72-dirty (Linux)
Using Irrlicht 1.9.0mt13
Using LuaJIT 2.1.0-beta3
BUILD_TYPE=Release
RUN_IN_PLACE=1
USE_CURL=1
USE_GETTEXT=1
USE_SOUND=1
STATIC_SHAREDIR="."
STATIC_LOCALEDIR="locale"

Active renderer

OpenGL 4.2

Irrlicht device

X11

Operating system and version

Debian GNU/Linux 12 (bookworm) x86_64

CPU model

Intel i5-3320M (4) @ 3.300GHz

GPU model

No response

OpenGL version

No response

Summary

This appears to be a regression of a previously fixed miscalculation in the anti-cheat system. It was supposed to allow the player to move as fast as allowed by in-game rules, including physics overrides, with a sufficient margin of error to account for lag, but it no longer works correctly.

Bisect identified the culprit as 8ebaf75 (New physics overrides).

This effect has been observed on both SP and MP servers, including servers in the wild running 5.8.0-dev. It doesn't seem to matter whether the terrain is being generated fresh, loaded from disk, or already in memory (not affected by emerge workload). I'm observing it on very lightly-loaded systems.

Affected Games

This appears to affect any game that sets a higher player physics_override speed.

NodeCore is affected out of the box.

MTG and DevTest are not affected, but can be by adding a mod:

minetest.register_on_joinplayer(function(player)
  player:set_physics_override({speed = 2.5})
end)

Steps to reproduce

1. Create a new NodeCore world, or world for another game that sets player speed physics_override.
2. /grantme fast,fly,noclip
3. Start flying around in wide circles (maybe like 80 diameter).

Expected

• Nothing unusual, you just fly around in circles.

Observed

• After a while (a few seconds to a minute) you will start getting position resets and "stuttering" movement, and your actual speed of progress will slow down significantly.

[sfan5]

This effect has been observed on both SP and MP servers

Anti-cheat calculations are disabled in singleplayer so this doesn't match up.

[Desour]

I managed to reproduce this in devtest. But it only works if I host a server, not in singleplayer.
5.7 is indeed unaffected.

[Warr1024]

Right, I forgot that my "SP" shortcuts all enable local hosting, so I'm just testing it on a server that doesn't have the latency issues of a real MP server, but I basically never run "true SP" mode.