Well I have been reading up on LOD AI, and given the fact that these are zombies eliminates a large percentage of the load we would normally have to contend with for an NPC.
If they weren't zombies, no one would give credence to NPC characters on a kamikaze mission, stepping over piles of dead bodies on there patrol. Also the animations frames can be tweaked without it being spotted so easily, and zombies tend to move in a jerky, simplisitic animation to begin with. So basically we are dealing with a large amount of entities with a One-Track mind!
Now what I have been reading about LOD AI seems to coincide wiht my intuition on the topic, but also defines more ranges, and tweak parameters. So here's a basic list of LOD
Off screen and faraway/close. Characters in this categroy are completely nonexistent to the player. When he's not seen, don't run his AI at all, because he's not influencing anything. You might want to continue playing his sound occasionally if he's close to the players location, but not if there is a selaed door between the player and him.
Very Far Off. A character in this LOD would be visible as a pixel or two. Stnad still. The view distance is so far tha even moving the character is unecessary because it will only translate to a few pixels worth of movement.
Far Off. Characters are now visible as solid colors, and possibly shapes, but no real detail yet. You can tell a monster from a humanois, and tell a truck from a car. Slide the character (don't animate, pathfind, or avoid, just slide) occasionally back and forth in a straight line. This will give the illusion of activity in the worls, without all the work.
Medium. This distance would be your true area of sight, determined more by the camera angles use in your game, as well as the depth fog starts to clear. A good distance mught be somewhere areoun 40 and 70 yards. For this disatance just run the regular AI becuase this guy isn't performing expsensive calcs.
Close. Anything closer than medium is considered close. Run the normal AI but adjust the update frequency level. The closer the character is to the player the higher the update freq.
Interaction The character is interacting with the player in some way. At this level, everything is on, and the AI is updating at the highest frequency level that it needs to make intelligent decisions.
Freq update and Load balancing. For characters within the human players immediate area, AI decisions might be updated very frequently, upwards of 10-30 times per second. For off screen elements, this might fall to a figure of 2-5 timpes per second or less. Nonessential behaviors (eye candy) can be reduced to not updating at all, if need be.
When setting up these schedules, try to load balance your update calls, so that you're not updating ALL of a SPECIFIC TYPE OF LOD level 3 every 15 game loops or ticks. Rather, offset their starting update time, so that each individual unit still only updates every 15 ticks, but only a few units of that type update each tick.
