> 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.

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.

I highly respect the implicit decision to forgo repeat purchases by merging into the original game, considering how much work was clearly involved. I haven't played it, but I hope for sustainability's sake, there are sufficient (purely cosmetic) microtransactions to cover their development costs.

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?

In my opinion one of the most impressive independent games published on Steam in the last years.

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

Looks like someone needs a better web host.

> Due to protection of web servers from repeated attacks, we were forced to restrict access to administrative interface of web pages to selected countries. If you are currently in a foreign country, please sign in to WebAdmin, proceed to your domain management and disable this GeoIP filter in OneClick Installer section.

"1.Serialize the entire scene, compress the data, and pass it to the joining client. We already do full scene serialization for quicksave and quickload, so this is possible, but the files are large: 30-50 MB is common, often more, so transfer would take a while.

[...]

3. Record the deterministic command stream, pass it to the joining client, and have that client apply all changes to the loaded scene before joining the game. The amount of data is much smaller than in option 2 since we’re not sending any voxel data, but applying the changes can take a while since it involves a lot computation.

Once we started investigating option 3 we realized it was actually less data than we anticipated, but we still limit the buffer size and disable join-in-progress when it fills up. This allows late joins up to a certain amount of scene changes, beyond which applying the commands would simply take an unreasonably long time. "

So [1] is not an option for players who want to do it that way?

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!

Looking forward to play the MP version with my son who also loves the game. I worry that the game will get heavier and maybe no longer work of the steamdeck, will it?

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.

For a bit more context, here's the announcement video:

https://www.youtube.com/watch?v=XfcCyMQ13XM

(Edit: fixed link)

do they have split screen multiplayer? I wish they did.

If only they hadn't stolen the idea at revision and then not paid the person they stole it from.

Douche bags.

(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!

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.

(not a teardown dev)

i had brainstormed a bit a similar problem (non world aligned voxels "dynamic debris" in a destructible environment. One of the ideas that came through was to have a physics solver like the physX Flex sdk.

https://developer.nvidia.com/flex * 12 years old, but still runs in modern gpus and is quite interesting on itself as a demo * If you run it, consider turning on the "debug view", it will show the colision primitives intead of the shapes.

General purpose physics engine solvers arent that much gpu friendly, but if the only physical primitive shape being simulated are spheres (cubes are made of a few small spheres, everything is a bunch of spheres) the efficiency of the simulation improves quite a bit. (no need for conditional treatment of collisions like sphere+cube, cube+cylinder, cylinder+sphere and so on)

wondered if it could be solved by having a single sphere per voxel, considering only the voxels at the surface of the physically simulated object.

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)?

Part of the problem with [1] is that you still end up needing [3] anyhow, because even if you've got a fiber-to-fiber connection, while the transfer was occurring the game world has moved on and you'll need to replay that anyhow.

But if you've got a solution for [3] that works completely correctly anyhow, then writing lots of code for [1] becomes redundant to that anyhow, even with save/load code sitting right there. Might as well start from the beginning and replay it anyhow.

One of the things I will often do that I sometimes have to explain to my fellow engineers is bound the rate at which we'll have to handle certain changes based on what is making them. If you know that you've got a human on the other end of some system, they can only click and type and enter text so quickly. Yes, you still need to account for things like copy & paste if that's an issue for your system, where they may suddenly roll up with a novel's worth of text, but you know they can't be sending you War and Peace sixty times a second. You can make a lot of good scaling decisions around how many resources a user needs when you remember that. The bitrate coming out of a human being is generally fairly small; we do our human magic with the concatenation of lots of bits over lots of time but the bitrate itself is generally small. For all that Teardown is amazingly more technically complicated than Doom, the "list of instructions the humans gave to the game" is not necessarily all that much larger than a Doom demo (which is itself a recording of inputs that gets played back, not a video file), because even Doom was already brushing up on the limits of how many bits-per-second we humans can emit.

fme, it's only kind of inconvenient. By the time the scene gets to the point where join-in-progress is disabled it's complete chaos anyway. Might as well restart the scene.

That said I haven't played any of the more intricate mods out there, but I can how it would become more of an issue.

They didn't explain those in detail because they didn't implement these concepts themselves. The GameNetworkingSockets library (and most likely also the internal network backend that was mentioned) provides them: > A reliability layer significantly more sophisticated than a basic TCP-style sliding window. It is based on the "ack vector" model from DCCP (RFC 4340, section 11.4) and Google QUIC and discussed in the context of games by Glenn Fiedler. The basic idea is for the receiver to efficiently communicate to the sender the status of every packet number (whether or not a packet was received with that number). By remembering which segments were sent in each packet, the sender can deduce which segments need to be retransmitted. https://github.com/ValveSoftware/GameNetworkingSockets

There really doesn't seem to be anything new or unique to their solution. I'm personally not surprised, because it is what has worked for thirty years.

I presume you know this, but maybe for others: judging by what was written in that paragraph, I'd indeed assume he means the same paradigm that has been driving replicated real-time simulations since at least QuakeWorld - some world-state updates (in this case _"object transforms, velocities, and player positions"_, among others) don't have to be reliable, because in case you miss one and need a retransmit, by the time you receive it, it's already invalid - the next tick of the simulation has already been processed and you will get updated info anyway (IIRC this is essentially John Carmack's insight from his .plan files).

The command messages (player operations and events) _need_ to be reliable, because they essentially serve as the source of truth when it comes to the state of the world. Each game client depends on them to maintain a state that is the same for everyone (assuming determinism the Teardown team has been working on ensuring).

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

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.

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

In addition to what others have said: even where remote play works, some games are worse candidates than others, and I expect Teardown would be towards the "worse" side of the set.

Teardown, visually speaking, is a pretty noisy game at times, and doesn't give a great visual clarity when streamed at real-time-encoding-type bitrates during these noisy moments.

FPS mouse+keyboard is also one of the worst-case scenarios for Moonlight/GFNow/etc. remote play, because first person aiming with a mouse relies very heavily on a tight input-vision feedback loop, and first person camera movement is much harder to encode while preserving detail relative to, say, a static-camera overhead view, or even third person games where full-scene panning is slower and more infrequent.

They targeted/ended up with a 1Mbit throughput requirement per player.

Please figure out a way to generate 1440p video at 90hz with pixel perfect rendering at 1Mbit per video stream.

Half the point of Teardown is that it looks really really good and crisp because it required a beefy GPU at the time it was released. I don't want blocky streamed video.

For me as a player that might have been a simpler solution to an entirely different problem. I don't imagine that playing a first person 3D game with free movement and platforming would be a pleasurable experience with the latency overhead of streaming video over the internet. That's part of the problem being solved here.

Might have been a key differentiator for Stadia.

Other comments are worrying about the streaming and latency but local split screen could also be another use case here.