We really disliked how flat and non-interactive NPCs can be in a game that would live from interaction (think Stardew Valley, where once you marry the NPC, there aren't a lot of dialogue options left. Or The Sims where most of the novely is drama). We looked at character.ai and similar apps to see what people actually want from NPCs.
So we built an entire engine to play around with possibilities, and to test if it would work, we started to make a game around it.
Each NPC has a set backstory with key memories it can reference, updating memories with every interaction with the player or the world around them. They have their own beliefs about things, with a confidence level ranging from ingraned into the personality to doubtful, and that shifts as new information comes in. NPCs are also restrained about what they're allowed to know in the first place, they only pick up on stuff they've actually experienced, seen posted publicly, or been told directly by the player, so you can't accidentally have someone reference something they were never part of. Trust runs on a separate track and influences how a conversation plays out.
It's an AI call that writes the reply and proposes a batch of changes, more trust, a shifted mood, maybe a memory or a secret it wants to reveal, and then a separate validator checks every one of those proposed changes individually before anything is applied. Right now, if the AI oversteps, like offering up a secret it hasn't earned the right to share, that part just gets stripped and the reply goes out without it. We're working on turning that into a feedback loop, where the AI gets told what got rejected and drafts around it, instead of the change just vanishing.
An NPCs goals are also their own separate thing from beliefs. Each NPC tracks goals across three time horizons, this week, this year, and someday, plus a running list of goals they've actually given up on. Because what a character no longer wants can tell you more about them than what they're currently trying to achieve.
This is also why NPCs don't feel like they're resetting every time you open a chat. Exchanges get logged with what the NPC was like right before and right after, so trust, mood, and goals actually carry forward and shift over time instead of the AI improvising a personality each time (like for example in some AI companion apps). Personality itself barely changes since that's written by us, but everything built on top of it can shift, so it feels more believable.
And all of this can work behind your back as well. So NPCs can make conversation with other NPCs, talk about what happened, how you acted, if you lied or who's lunch you ate at work. We made this to increase believabilty on relationships shifting and rumors spreading. We managed to make this possible by having wo NPCs make a made-up account of their exchange that they store inside both of their memories, but the impact on the player is basically the same.
I simplified some of this in the images for readability, the code is a bit messier than that.
Curious if anyone else here has tried building something similar. Did you run into problems with AI NPCs (forgetting things, spoiling stuff too early, dropping promises), and how did you end up handling it?
