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Comment by 10000truths | Hacker News Reader

> a lockstep solution which only considers inputs

Nothing stops you from adding a PRNG seed parameter to initialize your deterministic game engine.

That could lead to other subtle problems elsewhere though, because it requires synchronizing the seed. If you can't do that, it could lead to problems. E.g. when comparing offline speedruns where everyone would have a different seed. Then some players could have more luck than others even with the same inputs, which would be unfair. (Though I can't think of anything else at the moment.)

That's not more of a problem than synchronizing the player names at game start. It's table stakes for an online game.

If you synchronize the seed at game start for speedruns, the seed is the same for everyone, and players can again manipulate their luck, so nothing was gained.

If you run a game entirely between colluding parties, cheating speed runners can just hack it to do whatever they want anyway. See the Dream Minecraft thing from several years back. Speed running claims may be cheated in a thousand ways. It's up to the people who care about it to establish and enforce rules.

But if you're running a multiplayer game with random elements and aren't colluding, you don't have to let a malicious party set the RNG seed to whatever they like just because you agree on it at game start. There's any number of simple cryptographic protocols that allow each peer to contribute equally to the RNG state based on having a separate commitment phase. And it's a lot easier to run a quick cryptographic setup than it is to have constant input-driven adjustment.

Typical deterministic game engines will do this, send it to every machine as part of the initial game state, and also check the seed across machines on every simulation frame (or periodically) to detect desyncs.

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