what kind of latency budget do you have to do all that? even at like 15fps i cant imagine that you can provide a non janky experience when this “server yanks client back to valid state” move is done. i mean obviously you guys have figured it out, just the math doesnt quite make sense to someone like me not in gaming
The lag compensation is, more intuitively, just allowing the client to move on its own without needing server verification yet. The server maintains the authoritative game state, but (assuming no cheating is going on) the clients are able to move as they think they will. In the background, the client is actually sending its inputs to the server, and they technically haven't happened until the server verifies them (however many milliseconds later), but we allow the client to move on its own regardless.
The yanking back only happens if the client's new state (position etc.) don't match the server's state.
Think of it like the NTP protocol to for machines to sync wall-time. The idea is that there's an authoritative source of data, in this case the local time on the server. Your machine also does its best to independently track and maintain the current time. But it may be fast or slow, or experience some other issue that causes it to drift. And the longer its left by itself without syncing to an NTP server, the larger that potential drift.
So the server and the client are both independently calculating the state. But whatever the server calculates is authoritative, and the client's version is just a local simulation that is very accurate, but not 100%. Especially when it comes to other players, where your client is typically just executing under simplistic assumptions of things like constant forward movement.
However, luckily for the client, it receives a data sync from the authoritative server several times a second, so all that potential drift gets quickly corrected while the differences are still extremely small. For your own actions, where your client had access to all your input, the differences are probably even too small to notice. For other players though, it will be more noticeable, especially if there's an abrupt change in input.
