Not compatible game data

[Rodion Romanovich]

Hi!

I'm making a mod with improvements mostly for singleplayer. The only thing that's changed that'll also affect multiplayer are group formations. The problem is that when I change those, it's impossible to connect to vanilla R:TW games in multiplayer, because it says: incompatible game data.

The thing is that the changes I made do NOT affect multiplayer at all so the games should be compatible in mp even though the game says they aren't. Is there any way of overriding that limit?

My first experiment involved changing export_descr_unit.txt, changing type of royal pikemen to "heavy" instead of "spearmen" in order to treat them as a different unit type than phalanx pikemen in the edited group formations. When that didn't work I tried to put 3 nonsense characters in a comment to compensate for the 3 bytes less the file size became when I edited spearmen to heavy. That didn't work either. It seem like last edited date doesn't matter when compability is decided because I edited and edited back, then saved the vanilla .txt file and it was still compatible in mp. So - what is it that really determined compatibility and how can I make changes that won't affect multiplayer without the game saying game data is incompatible?

[Lord Adherbal]

compatibility checks are most likely based on some checksum formula. So changing even a single character in export_descr_unit.txt can cause incompatibility. Even if it wouldn't actual affect battle results.

[Rodion Romanovich]

Ok, thanks. And I assume CA is keeping that checksum algorithm to themselves to avoid cheaters from hacking the game? Hm, I might have to give up with my mod idea in that case.

[Rodion Romanovich]

But wait - the checksum of the file must be compared to some other checksum, right? Doesn't that mean the checksum must be stored elsewhere? Is it stored online, or just in another file, that I could edit?

[Lord Adherbal]

erm it's most likely stored in a variable in the memory and transferred to other players over gamespy. I don't think you can change that - besides, the whole point of compatibility checking is that you cannot bypass it :)

[Rodion Romanovich]

Yes, I think you're right. The only weak point in this fort is the calculation of the checksum from the file. I'll make some attempts and see if I can find at least one change of a file that does NOT lead to incompatibility and from that try to figure out the algorithm. It's likely though that the algorithm is too complex to be able to figure out just by testing.