[Exhumed] Strange slippery movement

[Dynamo]

Playing on 1.4.0, I'm noticing something I've not noticed before, there is some strange slippery movement going on in Exhumed which seems to depend on the angle you are facing for some reason?



As seen in this video, I take a step back using the s key, but the game keeps sliding for a time, then I take a step forward to the right and everything appears to work normally, but when I take a step to the left instead the game slides the player character slightly towards a specific direction in the left, which is always the same even when I move differently towards that direction. It's kind of hard to explain and probably to see but it's a bit distracting when playing, no clue if that is something that has always been there and I'm only now noticing it but it certainly feels like a bug.

[Graf Zahl]

This is something old. I currently have 1.3.1, 1.0.1 and 0.4.0 installed for testing and the effect is present in all of them. So it is very likely this comes from the original code (or at least PCExhumed.)

[Gammli]

This is also present in Duke3D. Here's an old report from eduke32 that noticed the same thing: https://voidpoint.io/terminx/eduke32/-/issues/103

Since it spans across games, it is most likely some effect inherited from the Build Engine base.

[Graf Zahl]

Indeed. The problem is most likely the low fractional resolution of the fixed point coordinate format. Build uses 28.4 for this, but 4 bits of fractional resolution is surely not enough. This can also easily be witnessed in SW on several sector objects where the textures twitch around when they rotate - the boat in the second episode's first map is a good example.
To really fix this the entire math needs to be transitioned to something more precise, but that is obviously a rather extensive task.