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The unlikely story of Teardown Multiplayer

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Re: The unlikely story of Teardown Multiplayer

#11

Post by DimitriBouriez »

dwattttt wrote: post #10
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.

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).

Re: The unlikely story of Teardown Multiplayer

#12

Post by kajkojednojajko »

I enjoyed playing Teardown when it first came out. It was already a technological marvel back then, so it's even more impressive that they managed to make the simulation deterministic to add multiplayer several years after release. Clearly top tier engineers.

Cool to see that the game is owned by Coffee Stain now, too. Satisfactory has been handled well by them, so I'm optimistic about the future of Teardown as well.

Re: The unlikely story of Teardown Multiplayer

#13

Post by filcuk »

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).

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.

Re: The unlikely story of Teardown Multiplayer

#14

Post by jmgao »

> 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 too bad because AMD and Intel tend to have intentionally identical implementations of most floating point operations, with the exception of a few of the approximate reciprocal SSE instructions (rcpps, rsqrtps, etc). Modern x86 instructions tend to have their exact results strictly defined to avoid this kind of inconsistency: https://software.intel.com/en-us/articles/reference-implemen...

If you want this to work across ARM and x86 (or even multiple ARM vendors), you are screwed, and need to restrict yourself to using only the basic arithmetic operations and reimplement everything else yourself.

Re: The unlikely story of Teardown Multiplayer

#16

Post by HexDecOctBin »

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 to ensure a global grid. But I have not been able to find any theory of Newtonian Mechanics that would work in discretised space (Movable Cellular Automata was the closest). I wonder if anyone in the Teardown dev team tried to solve this problem?

Re: The unlikely story of Teardown Multiplayer

#17

Post by DecoPerson »

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…

(I’m not a Teardown dev!)

I tried this on a local project. It looks very jank and the math falls apart quickly. Unfortunately, using a fixed axis-aligned grid for rotating reference frames is not practical.

One to thing I wanted to try but didn’t, was to use dynamic axes. So once an entity is created (that is, a group of voxels not attached to the world grid), it gets its own grid that can rotate relative to the world grid. The challenge would be collision detection between two unaligned grids of voxels. Converting the group to a mesh, like Teardown does, would probably be the easiest and most effective way, unless you want to invent some new game-physics math!

Re: The unlikely story of Teardown Multiplayer

#18

Post by VoidWhisperer »

kajkojednojajko wrote: post #12

I enjoyed playing Teardown when it first came out. It was already a technological marvel back then, so it's even more impressive that they managed to make the simulation deterministic to add multiplayer several years after release. Clearly top tier engineers. Cool to see that the game is owned by Coffee Stain now, too. Satisfactory has been handled well by them, so I'm optimistic about the future of Teardown as well.

It seems like Coffee Stain generally handles the games they publish pretty well. They also have Valheim and Deep Rock Galactic published under them, both of which have been reasonably successful and long running games

Re: The unlikely story of Teardown Multiplayer

#19

Post by kg »

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).

Most consumer GPUs have a limit on the number of video streams their hardware encoder can handle at once, and in some cases the limit is as low as 2.

Re: The unlikely story of Teardown Multiplayer

#20

Post by turtledragonfly »

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…

I'm sure you know, but for others reading: even on the same architecture, there is more to floating point determinism than just running the same "x = a + b" code on each system. There's also the state of the FPU (eg: rounding modes) that can affect results.

On older versions of DirectX (maybe even in some modern Windows APIs?) there were cases where it would internally change the FPU mode, causing chaos for callers trying to use floats deterministically[1].

[1] https://gafferongames.com/post/floating_point_determinism/ (see the Elijah quote, especially)

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