A few questions about techs

[Kemystul]

Okay to start, I'll set up a little scenario.

Lets say you have two lower tier techs, we'll call them "magic" and "divine", and we also have a higher tier tech, we'll call it "adv theory".

1. Is it possible to have the higher tier tech have EITHER of the lower tier techs as a requirement instead of both? (ex: having either magic or divine as the prereq to adv theory, but not requiring both.)

- 1b. If it's possible, is there an upper limit? (ex: like say adding "psionics" and "chi" to the "magic" and "divine" of the base scenario, making "adv theory" achievable by 4 different routes.)

2. Is it possible for a tech to make another tech forbidden? (ex: taking the religion tech makes it so you can no longer research magic)

3. Lastly, if this tech is given by a social policy, will it still follow the above rules? (ex: magic and divine are given by social policies, lets say you take magic first and get the tech, but then later choice you like the divine tree better, if taking magic makes divine forbidden, would you get the divine tech by taking the policy?)

 

[Galacticat42]

1. Yes in XML
1b. Yes in XML
2. Yes, but only through Lua/SQL.
3. Yes, but only through Lua/SQL.

 

[Spatzimaus]

Slight corrections to Civ Fuehrer's answers:

1> Yes, in XML, although the Tech Tree display won't draw any prerequisite lines if you do this.

1b> Yes, there are hard limits on the numbers of prerequisites a single tech/unit/building can have. Generally speaking it's 4, although for many OR tables (including this one, I believe) it's 3. So you can't make a tech that unlocks if you've learned any one out of twelve prerequisites. The game will simply stop checking after the first 3-4.
Also, you can't mix the ANDs and ORs. So you can't have a tech unlock if you've researched (A and B) OR (C and D).

2> This can be done through Lua, as he mentioned, but there's one MAJOR caveat: as with many other Lua changes, the AI won't understand this. It won't realize that the choice of A vs. B is a one-time thing; it'll pick one (let's say A) based on its preferences at that moment, and then not understand that it can never go back and get B.
It's actually easier to do if the techs in question are awarded through some other mechanism (buildings, policies, etc.) instead of being things the user researches normally. But it's still a problem regardless.

3> As there's no mechanism in place for a Policy to give a specific tech, this'd all have to be handled through Lua anyway. Policies can give N free techs, but they can't give a specific one, at least through XML. So you can set whatever requirements you want, then, although again, the AI would have no idea how it actually works.

The AI, in general, has no way to evaluate the effects of its choices; it doesn't decide to build a Factory because it thinks it needs a Factory. Instead, it says "I need more production", which skews its Production preferences higher, which makes it more likely to select a building that has a high Production flavor, which happens to be the Factory. Even if it thinks it really needs production, there's still a chance it'll decide to produce a Theater or Opera House instead, because it's all a question of probabilities at the moment the civ decides the next production target for a city.

The same goes for Policies. If you make a Magic policy that bestows a tech, then all that matters to the AI is what Flavor you attach to the policy. If you later decide that taking that Policy won't ACTUALLY give the tech because it's exclusive with that given by some other policy, then it won't change the Flavor on the policy, which means the AI will be just as likely to select it as before.