also ich hab mal gestöbert, weil ich grob in Erinnerung hatte, daß CB18 mal diskutiert wurde:

#openttd schrieb:[Mo Okt 20 2008] [01-34-29] <DaleStan> Yexo: Re: CB18. I have no clue. Check the source (grep for "18" and "callback" in the same line and go from there) or ask patchman.
[Mo Okt 20 2008] [01-35-43] <Yexo> thx DaleStan, but we already decided that we won't use cb 18 for NoAI (at least not for trains)

#openttd schrieb:[... geht irgendwie um NFO Version 8 ...]
[Di Nov 11 2008] [19-38-24] <Yexo> cb18 (and maybe others) cannot be extended for more rail types currently
[Di Nov 11 2008] [19-39-11] <frosch123> Yexo: you can add new subtypes to cb18. so it does not need a grf version bump
[Di Nov 11 2008] [19-40-35] <petern> cb18 is an abomination anyway :)
[Di Nov 11 2008] [19-41-22] <DaleStan> <petern> 0xffff is a callback value of 0x7fff <-- not so in v4-v7.
[Di Nov 11 2008] [19-42-56] <Yexo> http://rbijker.net/openttd/newgrf_ai_train_purchase.txt <- as alternative to cb18 for trains. I was told a change like that needs a grf version bump, so maybe this is the time to consider that.
[Di Nov 11 2008] [19-45-17] <frosch123> Yexo: That suggestion would restrict callback 18 to be a noai only callback, and would stop supporting TTDP AIs. You have to add a new value for variable 86 for noai stuff. Then you can do what you like, without any version bump.
[Di Nov 11 2008] [19-45-54] <Yexo> frosch123: I don't see why a TTDP AI couldn't use that callback
[Di Nov 11 2008] [19-47-39] <frosch123> you have to discuss that with a patch dev. but I guess they will happily await your patch -)
[...]
[Di Nov 11 2008] [19-52-55] <Yexo> still, the current cb18 has "82 B default selection" where "default selection" is an EngineID when features = 00-03
[Di Nov 11 2008] [19-53-04] <Yexo> ie it doesn't work with the engine pool

#openttd schrieb:[Sa Jan 24 2009] [00-12-35] <petern> so, er, did newgrf's ability to decide which engine/wagon to buy get implemented?
[Sa Jan 24 2009] [00-12-40] <petern> (i assume not)
[Sa Jan 24 2009] [00-14-10] <Yexo> petern: no, because the current callback only supports 8 bit values
[Sa Jan 24 2009] [00-14-36] <Yexo> and I didn't exactly get much help trying to get a improved callback implemented
[Sa Jan 24 2009] [00-15-07] <Yexo> petern: http://rbijker.net/openttd/misc/newgrf_a...rchase.txt <- latest proposal for a new callback
[Sa Jan 24 2009] [00-17-44] <petern> can't read that, what's the jist?
[Sa Jan 24 2009] [00-18-07] <petern> whats wrong with the existing callback?
[Sa Jan 24 2009] [00-18-41] <Yexo> CB18? 1) it returns 8bit values for EngineID
[Sa Jan 24 2009] [00-19-09] <Yexo> 2) for road vehicles and ships you can only do 'check', not 'get'
[Sa Jan 24 2009] [00-19-44] <Yexo> hmm, 2) also holds for the train engines is seems
[Sa Jan 24 2009] [00-21-25] <Yexo> 3) the current callback can only return 2 engine ids, 1 for the engine and 1 for the wagon
[Sa Jan 24 2009] [00-21-55] <Yexo> that means it can never propose a train with a caboose wagon for example (like nars requires for human players, but not for AIs)
[Sa Jan 24 2009] [00-22-24] <frosch123> however, yexo: variables 80..ff can only be bytes, and you should not replace the existing callback, but add a new type to callback 18.
[Sa Jan 24 2009] [00-27-10] <Yexo> I'd still like to see that callback implement (in some way), but it's currently very low on my todo list

Ich weiß nicht, ob das in irgendeiner Form deine Frage beantwortet, aber es zeigt wohl eine Tendenz auf...