Incompatible battle replays across OSes
 

In my first email game, I had the same problem twice: the battle replay I watched (on a Linux machine) was very different from the one announced in the Messages. The second time around, I took the time to watch the replay under Windows, and it was much more accurate.

This seems to indicate that the method used to store the replays is NOT compatible across platforms. I'd heard of replay errors before, but if my guess is correct, this will most probably kill my enjoyment of PBEM; I believe it's a serious bug.

I've read that the .trn files only store the random generator seeds, and the replays are recalculated by the game. If so, then it might be a simple inconsistency in random number generators, and reasonably easy to fix (add the same random number generator to all Versions instead of using libraries that might be incompatible).

Did anybody else notice this trend? I suppose most players are using Windows, but there must be a reasonable number of Linux/MacOS/Solaris Users too...

Re: Incompatible battle replays across OSes
 

Yes, it is VERY annoying!!! Watching your troops win a glorious victory, then looking at the casualty list to see that you actually lost, and all your leaders were killed. I didn't realize the problem was OS differences. Dumb C - that's why I like Java. Well, one reason.

-Cherry

Re: Incompatible battle replays across OSes
 

Hi Phil,
The OS "bug" would explain the strange things we observed in our game replays indeed http://forum.shrapnelgames.com/images/icons/shock.gif
Did you notice oddities in the Last turn's battles ? I was present in 3 of them and observed another between you and Abysia. On my Win machine the battles were consistent with the results (on the first battle the end of the battle was quite strange, with your winning troops suddenly all killed ...).
Anyway you should send the trn files to IW people so they examine what happens.

Re: Incompatible battle replays across OSes
 

The OS inconsistency is not related to the random number generator (hopefully) as Dominions uses its own random number algorithm. But something sure seems to be weird. http://forum.shrapnelgames.com/images/icons/icon9.gif

Re: Incompatible battle replays across OSes
 

and cant it be related to the rounding of some results, which would vary depending of the OS or the processor. Dunno how your algorithm works, but if it takes for example the 25th decimal of a number at a given time, like say

ln(0.123456789)
=
-2.091864070778393122967989 *7* 441961
on windows (being 7 there)
then perhaps it will be slightly different in linux.
?

Re: Incompatible battle replays across OSes
 

The random number generation itself should be foolproof. Only table lookups and some xor. Unfortunatelly the random number generation is only 0.0001% of what might go wrong, so your idea might still have some merit. The battles use sinus (sinf()) calculations and those might just be bad if those calculations should be significantly differnt on different machines. Definitely worth some thought... http://forum.shrapnelgames.com/image...s/confused.gif

Re: Incompatible battle replays across OSes
 

<font size="2" face="sans-serif, arial, verdana">If you are using gcc, the trig functions should all be implemented to the IEEE standard, which is to say that they should produce the same results across platforms.

This is not true if you use other C compilers, or if you use -ffast-math with gcc, as this allows the compiler to use the hardware trig functions, which in may cases (intel for one) do _not_ quite meet the ieee spec. Of course --ffast-math speeds gcc up quite a bit, as it avoids software Versions of trig functions (maybe sqrt as well?).

Of course, such differences should be tiny, so they should only affect actual results with miniscule probability (like one in a few hundred thousand).

Re: Incompatible battle replays across OSes
 

For me (a windoze user), a game running on a linux server results in about approximately every eight to tenth battle being completely different in outcome - the others look vaguely correct (including the numbers of creatures fled into neighboring provinces, etc).

Annoying, but then again, it's time for me by now to stop watching every battle replay and just go for the numbers...

Re: Incompatible battle replays across OSes
 

<font size="2" face="sans-serif, arial, verdana">If you give me an email address, I'll send you my latest turn file, where under Linux, my Arcoscephale army gets eaten alive by Hoburg-backed Abysian Infantry, whereas under Windows, the very same Abysian Infantry routed pretty quickly (and the naked Hoburg Crossbows were no match for Arcoscephale's armies, even ineptly commanded by me).

There were a lot of things that could go wrong in this battle - some arrows and bolts, some trampling, some spells...

Also, bear in mind that any tiny different result, if it means "die rolls" are then scheduled differently, can mean the whole battle's outcome is different. One arrow landing in a different square, once, could mean one unit is now dead, or has a different number of hit points, or takes a morale check, so that the same dice rolls will be used for something different from now on. You cannot accept any variability in functions that are used during the battle replays.

Re: Incompatible battle replays across OSes
 

I might add that I encountered this problem today in single player.

The review showed me a clear victory without any losses, the summary sais one of my commanders died.
And I'm very sure he is alive at the end of the replay

I'm using XP.

Re: Incompatible battle replays across OSes
 

I've seen this problem many times in MP game I play now and I'd like you to consider the possibility that it's not just the replay being incompatible between the platforms.

In one battle I had won with only 2 mercs left (of some weak variety). Usually these mercs rout way before they all get killed, so I can't realy imagine a scenario in which it would it be possible to win with only 2 of them remaining (opposition consisted of some indy forces). Of course, in Dominions it's impossible to foresee everything and there may be some explanation I'm missing. Replay was showing my mercs retreating pretty quickly after losing few comrades. And I had few other battles with weird results. Everytime, development in the replay looks quite logical and probable, but battle report sometimes produce results which I couldn't interprete at all (meaning that I couldn't imagine how the battle would have to be going to produce such results - as in that example with 2 mercs left).

From my cross-platform programming experience I would have considered that maybe some variable is left uninitialized and on different OS/compilers it gets initiaized differently which produces consistently wrong results in the case of one OS (or different wrong results in different OS). This could explain strange results due to altered battle mechanics.

Re: Incompatible battle replays across OSes
 

I actually have a scenario in which I could have won that. My serpent dancers all radiate powerful fear, and I had a good number of them in the battle. You by contrast had no priests. I had those cute little poison slingers. And my sauromancers were casting terror.

If your longbowmen were terrorized.... All I mean to say is that the outcome we got was possible. Not likely but possible. I lost a number of high defense serpent dancers there by the way. Not that they are equal to your giants.

Re: Incompatible battle replays across OSes
 

Another wild thought here. If you recompile Dom2 with different byte alignment and try to compare if the battle replay goes the same way in the old executable and the new one (on the same machine). If they're not going identically, surely there must be some uninitialized variables or memory overruns.

/Alex

Re: Incompatible battle replays across OSes
 

I have just installed and tried 'valgrind'. Seems like an excellent program to find variable that are used unitialized. Let's just hope it finds something interesting.

Re: Incompatible battle replays across OSes
 

We also experienced inaccurate battle replays. In fact the battle replays have absolutely nothing to do with the battle report.

We're playing a 2-player MP game with a Linux host and 2 Windows clients.

I hope you can find that bug. It's not really *that* important but the battle replay is really helpful for tweaking the army setup/spells. Especially for us newbies... http://forum.shrapnelgames.com/images/icons/icon12.gif

Re: Incompatible battle replays across OSes
 

Methinks that the totally inconsistent replays observed by PhilD rather show some problem/bug with the replay module itself than some n-th precision difference in the combat algorithm between various C++ compilers...

Re: Incompatible battle replays across OSes
 

We experimented a little bit more and don't have problems when hosting and playing on windows. I'm almost certain that this is a cross platform issue.

Re: Incompatible battle replays across OSes
 

<font size="2" face="sans-serif, arial, verdana">How do you people understand this stuff?

Re: Incompatible battle replays across OSes
 

It's technomancy. If you don't understand what any of it means, you're probably not going to unless you take up computer programming. Try researching the Technomancy school. This should make sense to you once you reach level 6 Technomancy or so.

Also, didn't this thread die ages ago? I recall the causes of the battle replay incompatibility was caused by differences in order of execution in the MR if() check?

[ March 18, 2004, 07:40: Message edited by: Norfleet ]

Re: Incompatible battle replays across OSes
 

Ja sorry I was searching. Shouldnt have replied. Sorry.