[TacticalCoder]

> 1) Bandwidth. The users internet can only handle so much network throughput, so for fast paced games (where you're sending data to each client at a rate of 20+ frames per second) it becomes important to optimize your per-frame packet size. This means using techniques like binary encoding and delta compression (only send diffs).

Games like Blizzard's Warcraft III / StarCraft II and Age Of Empire linked here in this thread (1500 archers on a 28.8 k baud modem) and oh so many other games approach that entirely differently: the amount of user inputs users can input is tinier than tiny. So instead of sending diff of the game state they send user inputs and the time at which they happened. Because their engine are entirely deterministic, they can recreate the exact same game state for everybody from only the timed user inputs.

Fully deterministic games engine also allow for lots of easy to reproduce bugs and they also allow for tiny save files.

Negligible network traffic. Tiny save files. Bugs are easy to reproduce. When the game allows it, it's the only reasonable thing to do.

[Armisael16]

This presents a (relative) vulnerability to cheating. If every computer has the full game state but players aren’t supposed to be able to know some things there is the potential for hacks.

The most obvious version of this in StarCraft is maphacks that let you see through fog of war, although that’s far from the only thing.

Poker meets all the technical requirements here, but sending everyone the contents of all hands would be a disaster.

[hitpointdrew]

> Poker meets all the technical requirements here, but sending everyone the contents of all hands would be a disaster

I work in the gambling space. A few notes, gambling games don’t ever rely on physics (even roulette, or a coin dozer type of game, everything is decided by a certified rng, no regulatory body that I am aware of allows outcomes based on physics engines). This means there is far less data to keep state on (a hand of cards is very tiny json blob to send). Games like poker etc. don’t require “real time”, if a player takes 4 seconds to decide if they want to call/raise/fold etc. then an extra 200ms of latency isn’t even going to be noticeable. So we don’t really care if there is a bit of latency, these aren’t FPS games.

[cornel_io]

Yep - even apparently physics-based digital casino games (think pachinko-style) are not allowed to use the real physics, that's really just faked as an animation to match the strictly controlled odds that can be easily verified by code inspection.

[flemhans]

That should be considered cheating!

Games that pretend to be physics-based but in reality have a backed probability engine.

[cornel_io]

People who gamble understand this, it's literally the law.

[dpedu]

This comes up in Minecraft too, and there was a small arms race around it. For the unfamiliar - certain resources in the game are useful and valuable but also rare (diamonds) and requires the player to spend a decent amount of time digging through the ground to find them.

But, since you have the whole game state, you can sift through the data and pinpoint these resources and acquire them quickly and with almost no effort. In multiplayer this is generally considered cheating and is called an "xray" modification to the game client. There are other variations of this hack that involve changing the game's textures to transparent images except for the specific resources you want to find.

Mulitplayer server administrators don't like cheats so they created countermeasures for this. The best example is probably Orebfuscator which "hides" said valuable resources until the player is very close to them.

https://dev.bukkit.org/projects/orebfuscator

[nwiswell]

Can't you still gain an unfair advantage using Bayesian search theory where probability drops to zero at the "revealing radius"?

Or is the "revealing radius" somewhat randomized over time in a way that's invisible to the client?

[Qub3d]

I mean, if you can acquire or otherwise reverse-engineer[0] the game seed, you can also just find resources by loading a local copy and noting the coordinates of ore. For major servers, anti-xray plugins will be installed as due diligence, but most of the anti-cheat efforts are focused on detection, reverting, and banning.

Ultimately, if you have a big enough server to attract serious cheaters, you will (or at least should) have tools that can also detect suspicious behavior based on heuristics (i.e. see if a player mined straight to an ore block). Tools like CoreProtect[1] can help detect and revert this.

Ore obfuscation still works very well, however, for the majority of causal cheaters that just googled "hacked minecraft client" and installed the first result.

One ore obfuscation technique used in PaperMC actually sends intentionally fake data to the user to "muddy the waters"[2].

(I know a lot of this because I help develop a Minecraft server management tool)

[0]:https://www.youtube.com/watch?v=GaRurhiK-Lk

[1]:https://github.com/PlayPro/CoreProtect/

[2]:https://docs.papermc.io/paper/anti-xray

[dpflug]

https://en.wikipedia.org/wiki/Mental_poker might provide a means by which you could have a match be verifiable by all parties after the fact, but not leak info during it.

[softfalcon]

Deterministic games suffer from desync and issues with input limitations. It is true that war3 does this, but it has some serious drawbacks.

It also makes the client easier to cheat on and gives one player (the host) a preferential ping.

Most competitive FPS’s use server authoritative instead of replayable deterministic because of this.

If you want to see the limitations, head into the old war3 map editor forums and look up the hacks using automated clicks between placeholder variable units just to move a few bytes of data between clients so they can persist character stats between games.

[elabajaba]

I never really got into SC2, but Warcraft 3 and AOE2 have pretty major problems with online gameplay due to using deterministic lockstep. Back in the day, it wasn't uncommon for people to lag out in Warcraft 3, which would freeze the game for the whole lobby until either enough time passed that you could kick them, or they stopped whatever was making them lag in the background.

My friends and I actually quit playing AOE2DE because about 1/3-1/2 of team games had someone lagging from the start, which makes the game slow and choppy for every other player (and this was despite the game having a benchmark you had to complete at a certain framerate to play matchmaking online). Spending the next hour in an unplayably laggy mess of a game just isn't fun.

I know Supreme Commander (supcom) also has problems with 1 player lagging causing everyone else to lag.

There's also the matter of it being much harder to actually program a deterministic game, especially once you try and multithread it (which is really necessary for modern RTS, but a nightmare for determinism). Fixing all desyncs is very difficult (AOE2 and WC3 both still have desync bugs. In AOE2DE some people use them to cheat their way up the ranked ladder, desyncing whenever they're losing so it counts as a draw instead of a loss). I've heard the upcoming Sanctuary RTS (indie supcom spiritual successor in development) talked to a bunch of RTS industry vets, and were told that it's not worth it to do a deterministic simulation these days unless you want over ~10k units. AI War 2 [1] has a pretty interesting network model for multiplayer, where they've got a semi-deterministic simulation, and self heal client's simulations if they diverge from the host, which allows for it to be heavily multithreaded and have 10k-100k+ units. You'd probably have to use dedicated servers for a competitive ranked mode if you went that way (and they'd be heavier to host, for a smaller per-game player count than eg. an fps or a survival game).

[1] https://wiki.arcengames.com/index.php?title=Category:AI_War_...