Board 8 > Can someone explain to me why rollback netcode is better?

(+) Yeah! (+)

As you may know, Arcsys just announced rollback netcode for Guilty Gear Strive.
I don't really have experience with it. I haven't played that many games online, and mainly ones that don't have it. It seems like having things undone would be pretty disorienting, even compared to input lag and slowdown. My theory was that it takes advantage of the frames when the remote player's input is locked or limited. If a connection dip happens there, it shouldn't matter much, whereas in delay systems it would still cause slowdown and/or lag. And maybe it would be inconsequential if the connection dips are small enough, versus a continuous small degree of lag. But what do you think or know?

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Delay-based netcode is literally nonfunctional garbage that should have been abandoned 10 years ago.

Rollback actually works and allows for smooth online play.

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Xiahou Shake posted...

Delay-based netcode is literally nonfunctional garbage that should have been abandoned 10 years ago.

Rollback actually works and allows for smooth online play.

Pretty much this. Overall it's just a much smoother experience.

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Sorozone posted...

Pretty much this. Overall it's just a much smoother experience.

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Delay ensures that at any point in time in reality, the same thing is happening on both screens, by waiting until it has everyone's inputs before simulating the next step. Rollback instead just keeps going ahead pretending it knows everyone's inputs, and when it gets the real input, it re-simulates everything from that past point up to now (hence "rollback") to fix the simulation.

So if you were watching both screens, you would see lots of inaccuracies in rollback, unlike delay. But if you're just watching 1 screen, it feels like they're right next to you, because both your and their actions are actually simulated as if they were instant.

The main problem with rollback is if the latency is too high then it will feel totally broken since the other player will be teleporting and your attacks will miss even though they hit. Most engines do have some delay to avoid the majority of that. But if you have a fast connection you don't need it.

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Ah, I see. The detailed explanation is what I was looking for but it's also good to know it really is way better.

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paperwarior posted...

Ah, I see. The detailed explanation is what I was looking for but it's also good to know it really is way better.

To go for an actual attempt at an explanation...

So online play has some kind of an clock to track frame count. As long as a players online clocks are aligned an online game could theoretically be flawless, but obviously theres things to worry about like persons internet quality, distance, etc

Delay is the old school method. When the clocks dont match up the game will stop until everyone is on the same page. Thats why online games with delay will show the frames of delay, its a prediction of how often the game will have to stop to wait for players input but it can easily be wrong. Once delay gets to like 7+ frames thats why it can take forever to feel like your button presses take forever to come out (if they do)

So rollback, when done correctly, is a way for the game to predict the actions of both players then auto correct itself quickly once the clocks are aligned. Unlike delay where you can feel the lag of your buttons not coming out, you can press buttons and they'll be consistently responsive. The main thing is what you see your opponent doing. If rollback is done well (Skullgirls, Killer Instinct) there might be very slight corrections on the opponents animations or position on screen but otherwise should feel seamless. However when done terribly (Street Fighter V) one person will both see input delay AND the opppnent will suddenly "teleport" to a completely different action and position cuz the engine did a terrible job predicting and autocorrecting what the opponent was doing.

So tldr rollback when done well is seamless and much harder to tell theres lag/distance. However, rollback done poorly is arguably worse than delay AND unlike delay needs to be built ahead of time to deal with clock based stuff of engine. Japanese have been using delay since that was the old school method thats been working and you know Japanese and old school...

@paperwarior Hope it helps

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Yeah. That is helpful. Thanks.

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A good rollback implementation will allow you to manually adjust the frame delay to account for the issues foolmo mentioned with high latency. No solution will help truly bad connections but rollback will help make what would otherwise be "tolerable at best" connections feel good

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Playing a fighting game in the US vs. someone living in Chile is true suffering

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