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Comment by esturk | Hacker News Reader

Does anyone know if rollback netcode works well in a 20+ player shooter game? I curious because the current craze of Battle Royals seems really taxing to the whole re-simulation of multiple frames within the window of a single frame.

Without being any less subtle, games like Apex Legends is known for really bad server performance, latency, and among other things.

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I'm a pretty avid Call of Duty fan and have been playing ther Battle Royale, Warzone, a lot lately.

Prior to this article, I've suspected there was some sort of predictive algorithm that helps make things smooth overall. I've noticed on a few occasions, I'll get shot by someone pre-firing a corner I haven't gone around yet (like sprinting to a corner to make a play). Several times, the kill cam has shown me fully around the corner for the other player.

I also have poor latency (my ISP routes poorly) and playing with friends that are geographically far - with servers even further away from me (though relatively close to them). It's a bummer that it happens, but I'm up to 200ms behind realtime. I suspect the game is predicting my movements - some of which put me in very bad positions, unintentionally.

Most FPS games suffer from “peekers advantage” due to the client side simulation of the player moving. Basically they can pop out or move around a corner and shoot before the movement has time to replicate from the server to you. The worse your latency the more advantage another player has.

I didn't know the term rollback before, but it seems to be exactly the same thing as lag-compensation which is what's the standard in shooter games since Quake. These are usually not peer-to-peer, but use a central server instead; the server retroactively applies inputs from all players (within their latency window for obvious anti-cheating reasons) which are not dead, though some games don't have the latter restriction, which enables players to trade kills even with instantaneous hitscan.

It results in the usual problems (peeker's advantage and being teleported backwards when a high-ping player kills you while you are moving) though it is not obvious how you can work around these.

There's generally not all that much point to rollback-style netcode in first person shooters, because you can just run asynchronously and do client-side prediction. If the prediction was wrong, it doesn't matter that much: you might have missed a shot and they're not quite where you expected they were. In fighting games, that's completely infeasible, because each player's actions are completely determined by the previous ones: either I hit you, and I'm going to continue into a combo that's very timing specific, comparatively, or you blocked the hit, and I'm doing something completely different.

Overwatch uses a rollback model but it’s not inherently or obviously better than other games.

It uses a fairly standard netcode where the state on a server is the only correct one. Battlefield 4 for example has a preference of a client state over the server in hit registration.

Yes but the game is deterministic and trades inputs which are rewound and resimulated. I don’t think the interesting part of rollback net code in fighting games is that it’s usually peer-to-peer. There’s a GDC talk on how it works here:

https://www.youtube.com/watch?v=W3aieHjyNvw

I know how it works. The only major difference for FPS is that there are multiple inputs inside a frame which have to be precisely timed. All the prediction models are either deceiving for a false reaction or the same "keep doing the previous action".

What you described is how sensitive a fighting game is. Which need to be 60FPS because moves are made within that limit with startup frames, active frames and move recovery on block vs whiff. The only FPSs that come close to FG levels of reaction/inputs is Quake, Unreal and maybe CSGO.

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