Nameless Voice on 30/6/2017 at 01:28

---

The settings in AI->AI Core->Vision Description activate different vision cones based on different awareness levels, but it doesn't look like the cones actually change between alerts 0 and 1.
Another thing of note is that the vision cones have Acuity - how well the AI can see. The higher the acuity, the farther away they can spot enemies from (including how close you have to be for different levels of alertness.)

-

I've been considering implementing a stealth system of my own, but I didn't get beyond some vague thoughts so far.
Depending on how much of the engine you are making yourself, you'll probably run into difficulty with how to detect light levels - the light level of an area is generally not something that the engine will expose to you, so you'll probably need to do manual calculations for it, or poke around in the engine's source code and add extra functionality. That will at least be easier for a 2D game than a 3D one.

-

Please don't listen to that advice about silent enemies and HUD indicators.
One of the things that Thief does perfectly, and why it is still considered one of the prime examples of an immersive sim, is because it conveys all its important concepts through believable in-game interactions. There are no HUD indicators or notification sounds breaking your immersion to give you information - instead, everything is conveyed through the world. The guards are unrealistically verbose, sure, but their vocalisations manage to tell the player about their state without once taking them out of the game's setting.