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The unlikely story of Teardown Multiplayer

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Re: The unlikely story of Teardown Multiplayer

#21

Post by gcr »

filcuk wrote: post #13
DimitriBouriez wrote: post #11

Earlier quoted context omitted.

That's true, I'm not saying it comes without trade-offs. But in return you get a perfectly consistent and physically accurate simulation. It would mostly be expensive, I think, but it's technically feasible (services like Shadow or GeForce Now already demonstrate that).

Which one of your friends can host an mp physics heavy game with a number of low-latency high-resolution video streams? I would estimate the average answer to be zero.

Perhaps the solution could be to have all players stream the game from a centralized instance, rather than all clients streaming from the host’s instance.

That would have a number of advantages, come to think of it. For starters, install size could be much lower, piracy would be a non-issue, and there would be no need to worry about cross-platform development concerns.

Re: The unlikely story of Teardown Multiplayer

#22

Post by dzdt »

jmgao wrote: post #14

> For the longest time (and for good reasons), floating point operations were considered unsafe for deterministic purposes. That is still true to some extent, but the picture is more nuanced than that. I have since learned a lot about floating point determinism, and these days I know it is mostly safe if you know how to navigate around the pitfalls. If you're only concerned about identical binaries on x86, it's not t…

At least in the early 2000s, Bloomberg had strict requirements about this. Their financial terminal has a ton of math calculations. The requirement was that they always had live servers running with two different hardware platforms with different operating systems and different CPU architectures and different build chains. The math had to agree to the same bitwise results. They had to turn off almost all compiler optimisations to achieve this, and you had to handle lots of corner cases in code: can't trust NaN or Infinity or underflow to be portable.

They could transparently load balance a user from one different backend platform to the other with zero visible difference to the user.

Re: The unlikely story of Teardown Multiplayer

#23

Post by Aeolun »

I really love Teardown, and I’m absolutely baffled at the bizarre performance that game manages to push on even very large worlds.

I’ve tried to load teardown levels in a homegrown engine and I always end up stuttering like hell as soon as GI becomes involved (or even before that).

I’m going to finally manage to replicate it, and then the new engine will be released and raise the bar again xD

Re: The unlikely story of Teardown Multiplayer

#24

Post by Aeolun »

HexDecOctBin wrote: post #16

If someone from Teardown dev team is here, did you guys ever tried to do the physics in voxel space? If I understand correctly, Teardown convert each physics chunk into a mesh and feeds all the meshes into a traditional physics engine. But this means that the voxel models remain constrained to the voxel grid only locally but not globally. I have been trying to figure out a way to do physics completely in voxel space…

You could project your dynamic objects to world coordinates, but it would look pretty wonky for small objects. A grid is just fundamentally not going to look very physical.

Maybe you could simulate physics but completely constrain any rotation? Then you’d have falling stuff, and it could move linearly (still moving in 3d space but snapping to the world grid for display purposes)?

Re: The unlikely story of Teardown Multiplayer

#25

Post by SiempreViernes »

HexDecOctBin wrote: post #16

If someone from Teardown dev team is here, did you guys ever tried to do the physics in voxel space? If I understand correctly, Teardown convert each physics chunk into a mesh and feeds all the meshes into a traditional physics engine. But this means that the voxel models remain constrained to the voxel grid only locally but not globally. I have been trying to figure out a way to do physics completely in voxel space…

This sounds like a fun thing to do simply for the pleasing global consistency, but the price you will pay is that the physics will inevitably look weird since all our intuition is for smooth space. In this sense it's like those games that try to put you into a 4D space, where the weirdness is sort of the point.

Not sure what you mean with the claim that Newtonian Mechanics doesn't work in discretised space? I'm know there are plenty of codes that discretise space and solve fluid mechanical problems, and that's all Newtonian physics.

Of course you need a quite high resolution (compared to the voxel grid in teardown) when you discretise for it to come out like it does in reality, but if you truly want discretised physics on the same coarse scale as the voxels in teardown you can just run these methods and accept it looks weird.

Re: The unlikely story of Teardown Multiplayer

#26

Post by Aeolun »

DimitriBouriez wrote: post #11
dwattttt wrote: post #10

Earlier quoted context omitted.

Video streams are not known for their low bandwidth needs, let alone adding in RTT latency for inputs.

That's true, I'm not saying it comes without trade-offs. But in return you get a perfectly consistent and physically accurate simulation. It would mostly be expensive, I think, but it's technically feasible (services like Shadow or GeForce Now already demonstrate that).

Running several raytracers on a single videocard isn’t free either. Syncing the world changes as they do is the least intensive for the server, and the last bandwidth. It’s probably optimal in all ways.

Re: The unlikely story of Teardown Multiplayer

#27

Post by xboxnolifes »

DimitriBouriez wrote: post #9

Wouldn't it have been simpler (even if technically heavy) to host the game on a single machine and just stream each player's camera? That way all the physics would be computed in real time on one computer, and each player would just receive a different video stream.

This seems to get brought up in every hn post on video game mulriplayer, and it makes me wonder: do you play video games? I dont know of any video games that do multiplayer that way, and i would think that alone suggests its not a good idea.

Who wants to play a game with 50ms+ keypress to screen update delay? Sounds miserable.

Re: The unlikely story of Teardown Multiplayer

#28

Post by hannasanarion »

I feel like there's detail missing in the blog.

The "Reliable vs Unreliable" section implies that different parts of the scene are sent using a strict-ordering protocol so that the transforms happen in the same order on every client, but other parts happen in a state update stream with per client queueing.

But which is which? Which events are sent TCP and which are UDP (and is that literally what they're doing, or only a metaphor?)

Really the economy of the text in the blog seems backwards, this section has one short paragraph explaining the concept of deterministic event ordering as important for keeping things straight, and then 3 paragraphs about how player position and velocity are synced in the same way as any other game. I want read more about the part that makes teardown unique!

Re: The unlikely story of Teardown Multiplayer

#29

Post by dwroberts »

hannasanarion wrote: post #28

I feel like there's detail missing in the blog. The "Reliable vs Unreliable" section implies that different parts of the scene are sent using a strict-ordering protocol so that the transforms happen in the same order on every client, but other parts happen in a state update stream with per client queueing. But which is which? Which events are sent TCP and which are UDP (and is that literally what they're doing, or on…

I would imagine it’s all UDP and the reliable+ordered is just a different mode which does the re-sending etc.

I would be surprised if they actually had TCP at all

Re: The unlikely story of Teardown Multiplayer

#30

Post by DimitriBouriez »

xboxnolifes wrote: post #27
DimitriBouriez wrote: post #9

Wouldn't it have been simpler (even if technically heavy) to host the game on a single machine and just stream each player's camera? That way all the physics would be computed in real time on one computer, and each player would just receive a different video stream.

This seems to get brought up in every hn post on video game mulriplayer, and it makes me wonder: do you play video games? I dont know of any video games that do multiplayer that way, and i would think that alone suggests its not a good idea. Who wants to play a game with 50ms+ keypress to screen update delay? Sounds miserable.

I don't play it much anymore, but I used to be a heavy player: the latency isn't 50 ms on GeForce Now (with a French connection, which is pretty good).
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