[vvanders]

Look into dead reckoning vs lock step for networking. Lockstep requires determinism at the simulation layer, dead reckoning can be much more tolerant of differences and latency. Quake and most action games tend to be dead reckoning (with more modern ones including time rewind and some other neat tricks).

Very common that replay/demo uses the network stack of it's present in a game.

[mjlee]

I used to be a professional sailor, and love finding nautical terminology in programming. At sea dead reckoning is navigating using the speed and direction of the ship, and adding tide and wind to calculate a fix based on the last known position. The term dates back to the 1600s.

It is fun to point at a chart and confidently state “We’re here! I reckon...”

[drzaiusx11]

There's a book I read a while back named "Longitude" that maps the storied quest in science to improve upon dead reckoning by devising greater and greater accuracy in time pieces used on ships. Iirc it was a fun read if anyone else finds that sort of thing interesting (as I do.)

[mjlee]

It's a great read! A story of how the scientific elite stalled progress because the right answer wasn't the one they hoped it would be, and didn't come from the sort of person they thought it should.

If you get the chance, you can see some of Harrison's chronometers at the Royal Observatory in London, though I don't know if they're always on display.

I'll add a recommendation for Sextant by David Barrie.

[drzaiusx11]

Thanks for the recommendation, I'll add it to the shortlist!

[sebg]

What other books do you like?

[drzaiusx11]

Pick a subject I guess, that's a really hard question

[sebg]

Last two books that you read?

[drzaiusx11]

"Build Your Own Metal Working Shop From Scrap" by David Gingery which covers everything from building a foundry to making all your tools from first principles using nothing but river sand and junk metal for smelting.

"On Trails" by Robert Moore that discusses how walking paths from the first peoples persist, grow and change over hundreds of years, along with advances in walking trail design in recent years to become a part time recreational activity vs the pure utility of terrain traversal as they first were. Covers how a trail is a "living thing", as it were, because any who tread on it help reinforce it. Covers non human trails like ants and their reenforcement via pheromones and the like.

[Jare]

I think the introduction of the term in networking simulations and games came with SIMNET https://en.wikipedia.org/wiki/SIMNET and continued more widely in the DIS https://en.wikipedia.org/wiki/Distributed_Interactive_Simula...

I first learned of it in some writing about a 1997 multiplayer game called, heh, Dead Reckoning.

[cubefox]

An interesting thing about the a lockstep solution which only considers inputs is that any RNG required in the game must be generated from the input history somehow. This could lead to players being able to manipulate their luck with extremely precise inputs.

[mackman]

The other interesting trick is you need a separate RNG for visual only affects such as particles than the one you use for the physics simulation. Depending on the game during replays, you could position the camera differently and then particle effects would render differently depend, depending on what’s on screen. Obviously that shouldn’t affect the way objects decide to break during the physics simulation.

[10000truths]

> a lockstep solution which only considers inputs

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

[cubefox]

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.)

[chowells]

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

[cubefox]

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.

[chowells]

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.

[Jare]

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.

[DonHopkins]

https://news.ycombinator.com/item?id=30359560

DonHopkins on Feb 16, 2022 | parent | context | favorite | on: Don't use text pixelation to redact sensitive info...

When I implemented the pixelation censorship effect in The Sims 1, I actually injected some random noise every frame, so it made the pixels shimmer, even when time was paused. That helped make it less obvious that it wasn't actually censoring penises, boobs, vaginas, and assholes, because the Sims were actually more like smooth Barbie dolls or GI-Joes with no actual naughty bits to censor, and the players knowing that would have embarrassed the poor Sims.

The pixelized naughty bits censorship effect was more intended to cover up the humiliating fact that The Sims were not anatomically correct, for the benefit of The Sims own feelings and modesty, by implying that they were "fully functional" and had something to hide, not to prevent actual players from being shocked and offended and having heart attacks by being exposed to racy obscene visuals, because their actual junk that was censored was quite G-rated. (Or rather caste-rated.)

But when we later developed The Sims Online based on the original The Sims 1 code, its use of pseudo random numbers initially caused the parallel simulations that were running in lockstep on the client and headless server to diverge (causing terribly subtle hard-to-track-down bugs), because the headless server wasn't rendering the randomized pixelization effect but the client was, so we had to fix the client to use a separate user interface pseudo random number generator that didn't have any effect on the simulation's deterministic pseudo random number generator.

[4/6] The Sims 1 Beta clip ♦ "Dana takes a shower, Michael seeks relief" ♦ March 1999:

https://www.youtube.com/watch?v=ma5SYacJ7pQ

(You can see the shimmering while Michael holds still while taking a dump. This is an early pre-release so he doesn't actually take his pants off, so he's really just sitting down on the toilet and pooping his pants. Thank God that's censored! I think we may have actually shipped with that "bug", since there was no separate texture or mesh for the pants to swap out, and they could only be fully nude or fully clothed, so that bug was too hard to fix, closed as "works as designed", and they just had to crap in their pants.)

Will Wright on Sex at The Sims & Expansion Packs:

https://www.youtube.com/watch?v=DVtduPX5e-8

The other nasty bug involving pixelization that we did manage to fix before shipping, but that I unfortunately didn't save any video of, involved the maid NPC, who was originally programmed by a really brilliant summer intern, but had a few quirks:

A Sim would need to go potty, and walk into the bathroom, pixelate their body, and sit down on the toilet, then proceed to have a nice leisurely bowel movement in their trousers. In the process, the toilet would suddenly become dirty and clogged, which attracted the maid into the bathroom (this was before "privacy" was implemented).

She would then stroll over to toilet, whip out a plunger from "hammerspace" [1], and thrust it into the toilet between the pooping Sim's legs, and proceed to move it up and down vigorously by its wooden handle. The "Unnecessary Censorship" [2] strongly implied that the maid was performing a manual act of digital sex work. That little bug required quite a lot of SimAntics [3] programming to fix!

[1] Hammerspace: https://tvtropes.org/pmwiki/pmwiki.php/Main/Hammerspace

[2] Unnecessary Censorship: https://www.youtube.com/watch?v=6axflEqZbWU

[3] SimAntics: https://news.ycombinator.com/item?id=22987435 and https://simstek.fandom.com/wiki/SimAntics

[dormento]

I love stories like these.

Btw video number [2] is private.

[cubefox]

Quite fitting then that it is called "unnecessary censorship".