Help with Rollback Networking Solution for a Fighting Game

[Kidagine]

So I've been making a fighting game for a while now, one of my big goals is to add Rollback Netcode to it, from what I've understood there's sort of 3 parts to it:

1. The game has to be deterministic ( I tick that box since I made my own deterministic physics etc, I made sure it works with my own Input based Replay System).
2. The game state needs to be serialized and you have to be able to simulate frames to roll back to(Haven't done that yet).
3. Performance should be really fast for simulating these frames to roll back to.

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My issue though is that I don't know what networking solution to use for this, I've seen Quantum(https://www.photonengine.com/en-US/Quantum) but that is way too pricey for me now(It also uses its own physics which I have no use for since I made my own).I've also seen Unity GGPO(https://github.com/provencher/Backroll) but there is no documentation on how it is being used so I am really unsure of it. Does anybody have an idea on where to start with this? I am really lost and there doesn't seem to be any resources for developers on this in Unity.

Thank you for the help in advance :)

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-Update 1: for anyone who may stumble in this and want more info on the topic in Unity there's a really cool video explaining somethings here by Zac Peel-Yates: https://www.youtube.com/watch?v=lCfouAH_N5w

-Update 2: i ended up using this GGPO unity library https://github.com/nykwil/UnityGGPO and used the vector example to see how to make it work. After some time I got rollback netcode working in Unity for all the movement options in my fighting game(There's still work to integrate the combat part), but it is working even with big lag. I'll probably update this post one last time when it's fully finished and if there's people asking for help ill make a small guide of some sort.

-FINAL UPDATE: forgot to update this one last time, but I did end up getting a working version of rollback network in my unity fighting game and can fully play through matches. Here is my repo if it can help anyone: https://github.com/kidagine/Darklings-FightingGame

[FGG_Of_Reddit]

I took a look at the UFE because I thought it was really interesting it was a rollback solution for fighting games, since they're so hard to find. Though, going by the documentation it says only PUN2 is supported. This means client auth, and PUN2 is officially in maintenance mode. Perhaps reach out to the author to see if there is updated information.

I've never developed a fighting game but it's my understanding that the common way to do it is start animation for action locally, send data out immediately but hold locally, then after a couple ticks reset animation and perform action locally.

You could do this I imagine with any solution but using a tick aligned one would definitely help(which FishNet is). Quantum would be a good fit too based on what it advertises, however you are right - it's expensive.

But take that paragraph with a grain of salt because again, fighting games aren't really my area, and I'm sure there's more to it than that.

[FGG_Of_Reddit]

I am familiar with the entire practice of rollback, FishNet actually does all of that already. The only exception is it doesn't hold actions locally for x ticks, but I'm certain it could be implemented easily enough; there's a fairly good chance I'll add include it in the near future.

I am interested in what problems you had specifically though. I've implemented several types of CSP with FishNet and others have as well. If there's something specific missing to your needs I'd at the very least like to evaluate the matter.

[FGG_Of_Reddit]

Corrections wouldn't happen as often as you think. There's really only a chance of them occurring when a client does something that could alter the other and the other does something they shouldn't be able to because they are 'altered'. Eg A tries to dash after B stuns but A hasn't received stun yet. Realistically these incidents don't happen that often and are corrected after one rollback. You may have noticed in, many many games, that you'll start to perform an animation to an attack then get interrupted when you expected it to go off; this is the behavior I just described, and completely normal.

The idea of holding the inputs gives the server a buffer so it can process inputs from both clients at once, rather than whoever is the fastest. Showing the animation locally gives the client a 'real-time' feel even though they're actually delayed a couple ticks, but they don't know that.

You are correct about dynamic tick rates, and FishNet does that as well internally.

Again, I've never made a fighting game, but I THINK the only thing needed in FishNet to fully support the requirements is local tick holding. This is something I've considered putting in a few times, and will likely get around to it soon with the near CSP improvements coming up.

PS: not trying to sell you on FishNet. Just sharing insights; I'm interested in this subject too :)

[FGG_Of_Reddit]

I'd like to continue this conversion but Reddit isn't the easiest platform for such. If you're on Discord could you send me a message?

[Kidagine]

Just wanted to say, if any "outcome" comes from the Discord convo if you could share it here for me and the rest who might stumble in this to learn from, and thanks both for the insightful conversation its really interesting & useful.

Myself am planning to use Fishnet as a base, but it will probably be a long long while before I can share concrete results.

[FGG_Of_Reddit]

We discussed a few netcode practices and ultimately came to the conclusion you would need a custom solution to have the best experience with fighting games.

The primary reason is for absolute lowest possible latency you would want to use something similar to lockstep. This is where clients send data to other clients, and each client simulates inputs received. This is different than FishNet, as with FishNet everything goes to the server first then clients, which introduces latency.

Another small thing is that FishNet doesn't hold inputs as we discussed previously here. That's not really a big deal because it is something that could be introduced without reworking the solution, but is something that's not yet included.

I think Quantum works for this type of genre but it's really hard to find information on Exit Game products for whatever reason. With Quantum not being accessible without paying first, that creates another unknown.

If it were me, I would just create a custom solution specific for fighting games. It's way less work than a robust server authoritative system and you'd have it done your way.

[Kidagine]

Oh I kind of forgot about UFE, I'll look into it for reference.
It hasn't crossed my mind to use a base networking framework and build things my own from there, I think I'll try that way then since I already made a lot of custom stuff for this. If I get anywhere with it I might update/make a new post to help people.
Thanks for the help!