Deterministic physics (for replays/ghosts).

Hey all, I am making a racing game and using the normal unreal physics.

I am currently part way through a big old project to make it deterministic (Which is bigger than I expected).

Getting it to run fixed step has been easy, but the two areas of challenge so far have been

\- Board inputs and controls (This one didn't surprise me)

\- Surface detection

It's coming along, and I am fairly sure it will be at the point where I can have ghosts soon.

I know it might not be determinisitic across platforms, so I am going to also record transforms and use them as a backup.

And now the all important "Question I should have asked before I started" - Has anyone got any advice or thoughts on deterministic physics? (I have been running tests throughout to confirm same output at different FPS).

Also, I am on 5.8.

Foot Note - I've been developing for years, and this is one of those uncomfortable rewrites where you need the whole thing to prove the plan works. (So the hop from safe state to safe state is waaaay larger than I would like).