Typically a fun Thief map works like this:

Entrance: This is usually a safe area (no guards in the immediate area and no patrol paths, so if you stay in one place you are safe), like out on the street or beyond the wall of the grounds. From here there are multiple entances (2-5) to the "level" itself - one should be fairly obvious (like an open window to a well lit, empty room) while the others should be obscured and have varying amounts of time to enter - thief players like to explore, and they like their exploration to pay off. For example if our level had 3 ways in, and we already covered the obvious one (window), the next entrance might be a cell door that's hidden by overgrwoth (those double door deals that a low to the ground at an angle), which takes the player into the basement of the level. The last entrance would require more then just observation while taking the "move in the direction of the goal" path - it would require that the player go off the path to explore the world, perhaps finding that the servants house can be broken into (where the player will find a small piece of loot), and by following the stairs they can get onto the roof, from where they can jump onto the roof of the main building, which the player walks across and finds a skylight they can open and drop down into.

Compartments: Thief levels are usually divided into compartmentalized spaces (this helps the AI pathfinding, makes design easier, and gives the player at least a fighting chance of creating a mental map [Thief has no "exact" map, just hand drawn notes, so sometimes you go in circles, all part of the fun]). Each compartment is composed of interconnecting rooms and passage ways - there is more then one way to get from almost any one point in the compartment to any other point. A typical example is a square looped hallway - you have a hallway that makes 4 90 degree turns, thus folding back on itself. On the perimeter you have rooms and some of those rooms connect to their neighboring rooms or connect to other compartments, while inside the square you have more rooms, some of which have multiple doors to the hallway (i.e. they are in the corner and have a door to two different facing hallways) and some of which are to other rooms. The central idea is that the layout of the compartment is not linear - it feels more like a musuem, with many exibitions that are interconnected to allow freeform exploration.

Plot Points: Usually compartments are connected in a semi-linear fashion. This means there are early encountered compartments (the "entrance" can be thought of as a very open compartment itself), middle compartments, and late compartments that come together to describe the "story" of the level. For example a level might have the entrance compartment, which has connections to the west wing of the buildings (a compartment). The west wing has connections to both the east wing compartment, and the greenhouse compartment, and both of those compartments have connections to the basement compartment, where the vault and ultimate objective is kept (and there is probably one secondary objective in the green house and one in the east wing). The point of this is so that while the player has free exploration and so is basically writing their own story, they still can't jump right to the "end" of the levels story, they have to progress through the beginning and middle first. While thief has locked doors (which can normally be picked or opened with the correct stolen key), there are often "hard doors". Hard doors don't have to actually be doors - they are choke points, single (though sometimes the player may have a choice, each with a different challenge) passageways, often connecting an earlier compartment to a later compartment. To get by these hard doors the player must overcome some task - in games without a lockpicking kit, this is where the player would be expected to go find a key. However since you can pick locks, the challenges are handled differently. A hard door might be a drawbridge you need to lower in order to enter the inner keep (after having passed through the compartments that make up the outer keep), or a tight corridor with some seemingly impossible to pass guard.

Goals: The primary goal is placed in the compartment furthest from the entrance. Secondary objectives are spread around the other compartments, sometimes requiring travel between several. Getting to/completing the final objective or getting through hard doors can also require travel to several different places, to throw switches or collect items. Often the actions the player needs to take to complete the primary or secondary objective (say for example open the draw bridge) are described in clues - perhaps a guard mentions some mechanical fault in a pre-scripted conversation triggered when the player gets near, or the player finds a document giving clues about the location of three levers that must be thrown in the correct sequence.

I think the event AI could work in a similar way to the Halo AI. Any event has 'precursors' or triggers that need to be fulfilled in order for that action to take place. Dialogue and other fun and interesting events run off the triggers, a random generator and possibly a repitition timeout (to stop repition or events).

In terms of implementing this for the complex interactions (involving one or more entities) I don't really see any optimisations other than periodically testing a bunch of them (ie two guards, a guard and a dog etc.) and then randomly choosing an action that incorporates the situation. It only really needs to be tested every 5 seconds or so for the generic interactions.

[Edited by - umbrae on November 5, 2005 8:18:46 PM]