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On Enemy AI and RNG (and the potential "instability" of bookmarks/battle saves)


ruadath
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I meant to make this post a while ago, but I've discovered something interesting about the enemy AI mechanics from my playthroughs of Awakening and Fates on emulators. As you might imagine, there are times when the enemy AI has to make a "random" decision about what to do, usually involving choosing between two (or more) equally good spaces from which to attack one of your units.

So how does it go about doing this? Well, in GBAFE and FEDS, the game would just burn some RNs from the standard RNG to make the decision. In Radiant Dawn, something more complicated goes on which I don't completely understand and won't elaborate on here. In FE3DS, however, it appears that the game uses a separate RNG string (sort of like the one that has been used to prevent arrow retracing RNG abuse since FE10) that is time dependent. What this means, is that under certain circumstances when you make a Bookmark/Battle Save, you are not always guaranteed to get the same results upon reloading your Bookmark/Battle Save!

Due to the (rout) nature of most maps in Awakening, this doesn't really matter much there, since enemy units that attack you usually end up dead anyway. But for Fates, it has some striking consequences due to the enemies' ability to utilize the Dual Strike system in the game. I could go on to explain this in detail from a theoretical perspective, but I think an example would be much clearer.

nVNdBHK.png

Consider the above situation (taken from Chapter 11 Conquest). Bow Knight!Niles is equipped with a bow, and on the enemy phase (once I end my turn) the Lunge!Ninjas will all swarm and attack him from up close. I make a Bookmark save here. When I reload and end my turn, for the first Ninja that attacks, going from left or above is "equivalent" in terms of AI priorities, so the decision is randomized. But depending on which one is chosen, different situations can occur! For example:

qMARNuV.png

7faeEaD.png

In the second screenshot (where the first Ninja decided to attack from the left instead of above), the Ninjas end up forming a box around Niles which results in one extra attack on him (due to a DS proc) that didn't occur in the first scenario. This of course causes a shift in the battle RNG, and goes on to have consequences (i.e. different results) in the other parts of the map as well. And these aren't even the only 2 possiblities; I found another one where the Ninjas form an L-shape to block Camilla's path forward too! And remember, these all come from the same bookmark!

So yeah, just an interesting tidbit of information that I thought you guys might enjoy. Let me know if it's not clear from the above example why the bolded statement is true and I'll try to explain it from a more pedagogical perspective.

Edited by ruadath
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They are? I just copied them straight from the thread I sent to you, and they seem to be working for me... I'm not sure what the problem is. Can other people see them?

Edited by ruadath
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Huh. Looks like a browser quirk on my end (as they display fine in a different browser), and I think I'm the only one on SF this will affect. The pics were also gone in the original PM, and I exercised a bit of creativity to display them.

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  • 3 weeks later...

Interesting. Nothing like this has happened in my experience; battle saves at least save RNG, meaning that you have to make a different sequence of movements for different results.

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PP stuff will always be the same, and usually EP stuff will too. It's only in these somewhat rare situations where the square that the enemy moves to matters in some larger context, but the enemy AI can't figure out which is optimal, that stuff like this happens.

This happens in Awakening too btw, and iirc it has been giving Espinosa problems with his 0% growths run of that.

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  • 1 month later...

I also did this when I wanted to see if I could save a Fallen unit by repeating the same actions in a bookmark.

It had the same results (they died) but the formation of the enemies can vary

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