This is why CoH2 will have per platform multiplayer

[[FERAL] Ellie]

Edit: Mac vs Linux cross-platform multiplayer is now supported in Company of Heroes 2 and its expansions.

It wasn't possible to support cross-platform play for Company of Heroes 2 for a number of reasons; and each of those reasons is itself multifaceted. Some have asked for a technical explanation, so brace yourself for a flavour of the challenges that cross-platform multiplayer support can bring.

Company of Heroes 2 uses a deterministic engine, and relies on clients to generate the same outcome for all gameplay-relevant calculations, like pathfinding, unit positions, spawns and combat.

Any differences in the maths, even at the nth decimal place of precision, will accumulate to a tangible divergence in behaviour and ultimately a disconnect. When dealing with multiple architectures, operating systems and optimising compilers, tracking down all possible differences is a long and complex task.

During development, cross-platform multiplayer was absolutely one of our goals and we invested countless man-hours in isolating and resolving these subtle differences. And although we made progress on some of these issues during development, it's impossible to know how many issues remain and how much more work would be required on ALL platforms to get the title communicating successfully across Mac, Linux and Windows.

Given all this, we took the decision to release the title with per platform multiplayer and keep investigating to see if multiplayer will be possible via a post-release patch. But because of the complexity and the various unknowns, we believe this is unlikely.

As anyone who knows our work is aware, we have a good track record of going the extra mile (or three) to add polish and functionality to our releases. However, in this case the quantum of work versus the low likelihood of ultimate success means that that we have had to compromise.

That's why we want to encourage Mac and Linux gamers to join this Steam Group, which should make finding participants for CoH2 Mac v Mac and Linux v Linux sessions easier.

[TAW|REA]

Thanks for the explanation.

[B.Lastbar]

Thanks for the explanation, it is very insightful. I value your good communication as a developer.

[Zeroedout]

That's really unfortunate but just part of the tech in a game like this. I'll probably still buy the game though... But no cross platform multiplayer makes it very hard to justify.

[FwSchultz]

That's very sad to hear as it effectively means that we'll be playing on Windows for the forseeable future since not everybody will have a Linux installation. But thank you, Feral, for trying!

Just out of curiosity: may we ask which compilers are you using on each platform?

And the short explanation above sounds somehow like one build is using compiler dependent fast math instead of IEEE fp computations. If this is the case, would it mean that the biggest problems could be solved by Relic by rebuilding the Windows build with standard fp and patching existing Windows installations?

Thanks again for trying hard and communicating it to the players!

[imolit]

Originally posted by FERAL Ellie:

Company of Heroes 2 uses a deterministic engine, and relies on clients to generate the same outcome for all gameplay-relevant calculations, like pathfinding, unit positions, spawns and combat.

Any differences in the maths, even at the nth decimal place of precision, will accumulate to a tangible divergence in behaviour and ultimately a disconnect. When dealing with multiple architectures, operating systems and optimising compilers, tracking down all possible differences is a long and complex task.

So this is basically a problem with mathematics? Aren't there cross platform libraries available which ensure that calculations are the same regardless of platform?

I do not know what the game code looks like though, so changing the way calculations are performed everywhere might not be feasible.

Thanks for being forthcoming about the information, though. I really appreciate the quality work that goes into Feral's ports.

[[FERAL] Ellie]

Thanks everyone for your understanding. See, this is why we always try hard for you lot!

Originally posted by FwbSchultz:

And the short explanation above sounds somehow like one build is using compiler dependent fast math instead of IEEE fp computations. If this is the case, would it mean that the biggest problems could be solved by Relic by rebuilding the Windows build with standard fp and patching existing Windows installations?

Originally posted by imolit:

So this is basically a problem with mathematics? Aren't there cross platform libraries available which ensure that calculations are the same regardless of platform?

Thanks for your thoughts, both, but there's no single change that would fix the majority of potential issues. It’s a combination of many things. Rest assured we've looked into this from many angles before making the decision we did.

[ZED]

Thanks for your answer.
Can be at least Mac vs Linux ?

[Roland Gunner]

Interesting. Fortunately I pretty much just play AI matches so it won't make much difference to me.

It seems like if this is a consistent problem that some kind of math library that matches Windows results could be helpful across all titles. I don't want to just see Wine "ports" but could their libraries be helpful here?

[[FERAL] Ellie]

Originally posted by ZED:

Can be at least Mac vs Linux ?

Unlikely. We tried. :)

Originally posted by Roland Gunner:

It seems like if this is a consistent problem that some kind of math library that matches Windows results could be helpful across all titles. I don't want to just see Wine "ports" but could their libraries be helpful here?

I'm afraid that's not useful when developing a native application, but thanks for the suggestion.

[WaylanderPK]

Big disappoint for me, all my friends have COH2 and use Windows. We were looking forward to busting it out at a net day. Cest la Vie. Would it be possible to release a 'beta' version with the cross multiplayer work so far. I would be up for testing it even if it fails more often than not.

[[FERAL] Ellie]

Originally posted by computerwizard:

Would it be possible to release a 'beta' version with the cross multiplayer work so far. I would be up for testing it even if it fails more often than not.

If any such version becomes available, we'll let you know, but do please remember that it's unlikely.

[JohnMcClane]

Realy? Why other games in CS:GO, Dont Starve, Left 4 dead and etc. have a cross-platform game, but you do not have?

[[FERAL] Ellie]

Originally posted by John_McClane:

Realy? Why other games in CS:GO, Dont Starve, Left 4 dead and etc. have a cross-platform game, but you do not have?

Hi John. We've released many games that support cross-platform play, like the F1 series, DiRT 3 and XCOM: Enemy Unknown.

However, not all games are designed the same. For instance, XCOM: Enemy Unknown is not designed the same as Company of Heroes 2. We always support cross-platform play when possible, but in some cases it simply isn't. We appreciate that people want to know why it wasn't technically possible in this case, which is why we wrote the explanation in the original post.

[JohnMcClane]

80% of the players in CoH2 only play multiplayer.
Why then do the port was made .... I am very disappointed.
will have to continue to play under windows on my Mac

[JohnMcClane]

Yet in the future, possible cross-game or not?