When I first started out on Vampyr, I was still getting familiar with Unity. I’ve been building AI in Unreal for a while, but had only dabbled with stealth AI on one particular project. I was using Game Creator for the player package, but wanted to see what I could do in C# for the AI. The results were difficult to tune and had lots of edge cases. I was focused on sketching something out, and wanted to avoid the common trap of over-engineering, which would probably have sucked the momentum out of my side project.
After I had done my first pass on some stealth encounters with that basic AI, I moved onto to other elements of the game and stood those up. For those, I found the Game Creator modules for Dialog and Inventory to be really useful for getting things roughed in. So when it came time to revisit the stealth AI, naturally I grabbed the Behavior and Perception modules. Unfortunately I found the Behavior module to be lacking compared to the workflow I was used to in Unreal. After a few attempts at rebuilding an AI with those tools, I was losing steam.
I did some brainstorming and whiteboarding in Miro, and the idea that really stuck with me was this. Build a state machine in C#. It doesn’t have the nice visual representation of the tools I’m used to, but it is reliable, debuggable, and not such a big undertaking that I won’t follow through. The big inspiration for me was the Demon Player state machine we used when developing Doom 2016. I followed what I recalled of that architecture and built this:
The state machine ties into Game Creator’s Perception module, but side steps the parts that don’t work quite how I’d like. I’ll probably rewrite that code later…
The AI brain is a component, which is a State Machine. The State Machines, and their states, are all code driven. I use C# generics (which I’ve learned, work somewhat differently than C++ templates 😅) in order to provide a generic state machine structure which has concrete implementations. Once I got a basic version stood up, I quickly found value in making it hierarchical. This allowed for easy separation of concerns: each state had to only worry about cleaning up its state if it was interrupted (potentially by a higher level transition).
This “Nouveau AI” is still a work in progress. I’ve implemented my first pass with Sight, patrols, and scripted behaviors, but other senses and behaviors must still be implemented before I can complete my existing encounters I’ve blocked out - at the quality I’m looking for. When I’ve done a more complete overhaul of my “Stealth Lab”, I’ll record a playthrough and post it here.