> 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.
dzdt 1 hours ago [-]
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.
turtledragonfly 2 hours ago [-]
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].
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.
VoidWhisperer 2 hours ago [-]
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
bjord 6 hours ago [-]
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.
prox 5 hours ago [-]
He is already talking about the new engine at the end, so maybe that means a new game/version.
Anyway I recently bought it because of multiplayer. Can’t wait to try it out.
hannasanarion 41 minutes ago [-]
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, which 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!
dwroberts 26 minutes ago [-]
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
HexDecOctBin 3 hours ago [-]
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?
DecoPerson 2 hours ago [-]
(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!
SiempreViernes 51 minutes ago [-]
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.
Aeolun 51 minutes ago [-]
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)?
Aeolun 55 minutes ago [-]
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
tietjens 5 hours ago [-]
In my opinion one of the most impressive independent games published on Steam in the last years.
esperent 5 hours ago [-]
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.
Sweepi 5 hours ago [-]
"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?
florbo 5 hours ago [-]
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.
DimitriBouriez 4 hours ago [-]
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.
xboxnolifes 41 minutes ago [-]
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.
DimitriBouriez 2 minutes ago [-]
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).
dwattttt 4 hours ago [-]
Video streams are not known for their low bandwidth needs, let alone adding in RTT latency for inputs.
DimitriBouriez 4 hours ago [-]
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).
filcuk 3 hours ago [-]
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.
gcr 1 hours ago [-]
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.
Aeolun 49 minutes ago [-]
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.
kg 2 hours ago [-]
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.
DimitriBouriez 1 minutes ago [-]
Okay, I didn't know that
xecaz 5 hours ago [-]
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?
stainlu 3 hours ago [-]
[dead]
Rendered at 13:21:25 GMT+0000 (Coordinated Universal Time) with Vercel.
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.
They could transparently load balance a user from one different backend platform to the other with zero visible difference to the user.
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)
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.
Anyway I recently bought it because of multiplayer. Can’t wait to try it out.
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, which 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!
I would be surprised if they actually had TCP at all
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?
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!
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.
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)?
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
> 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.
[...]
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?
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.
Who wants to play a game with 50ms+ keypress to screen update delay? Sounds miserable.
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.