Navigation

An enemy hunting you through a level carries a map of it, made in advance: a web of places it can stand and the ways between them. Navigation searches that map for the cheapest route that this particular body can take, right now, and hands it to the enemy one step at a time.

13

kinds of link between places

7

ways an enemy can be moving along a route

0

dice rolled to choose a route

As of 2026-10-22.

A map made in advance

The map is baked: worked out from the level once, ahead of play, and shipped with it. The bake probes the level column by column, feeling for every floor, and lays a grid of places where a body could stand. Then it adds further layers for the bodies that need them: low spaces for crawlers, open air for flyers, pools for swimmers, walls and ceilings for creatures that climb them, and the ladders, portals, doors and lifts the level hands in. A level switches on only the layers its creatures use. A big level is baked in pieces, and only the pieces that changed are worked out again. A level can also mark areas an enemy must never enter, or should prefer to avoid.

Places are joined by links, and each link says what kind of movement it takes: walking, stepping up, dropping off a ledge, jumping a gap, climbing a ladder, riding a lift, going through a door or a portal, swimming, flying, walking on a wall, or pulling up over a lip. That is what lets the search ask "can this body do that?" about every step.

Can this body take this link, right now?

The map itself never changes when a door shuts or a lift leaves. Instead, every link is asked a question each time a route is searched, and again each tick while an enemy is following it:

1. Can it ever?Does this kind of creature walk, climb, swim, fly or grip walls?
2. Is it safe for it?A drop it would not survive at its current health, a liquid it would drown in, or a no-go area all say no.
3. Is it open now?A locked door, a lift that has left, or a portal that no longer leads anywhere.
4. Does it fit?Is there room for this size of body, standing or crouched?

Doors show how this works. A locked door is never a route, whatever the creature can do: the key is the way through. An open or opening door is fine for anybody. A shut one is a route only for a creature that can open doors, and it does so when it gets there. Because health is part of the question, an enemy wounded on the way can change its mind about a drop it was going to take.

Choosing the cheapest route

Among the routes a body may take, the search picks the cheapest. Every link costs its length, and a few things add to that cost. Nothing ever subtracts from it, which is what guarantees the search really finds the cheapest route rather than a nearly cheapest one.

That personal variation is worked out from each enemy's identity, not rolled, so the same enemy in the same situation always picks the same route, and a replay plays out exactly as the game did. Searching is also shared out across ticks, so a whole pack hunting at once never stalls the game; an enemy whose search does not fit this tick asks again in the next.

Following the route

Navigation does not decide where an enemy wants to go; its decisions do. An enemy chasing you hands in where it can see you, or where it last saw you, and navigation only answers "which way from here". Up close it skips the map and walks straight at you. It searches again every so often, and again at once if the map has changed.

• Portals. An enemy walks into the portal itself, not past it. Friendly enemies take turns so they do not land on top of each other; a hostile one walks straight in. Nobody waits for ever.
• Lifts. An enemy walks onto the lift and lets it carry it. If the lift is parked or paused, it calls it. If the lift does not move for too long, it gives up waiting and goes back to its usual behaviour.
• Ways of moving. Along a route an enemy is walking, climbing, swimming, flying, wall walking or mantling over a lip; or stranded, like a fish on dry land, with nowhere it can go.

What enemies do once they arrive, from searching rooms to fleeing, is on the what enemies can do sheet.

When the level changes

A game can change the map while the level runs: drop a ladder into a shaft, flood a corridor, open a new portal, or lose a ladder section to gunfire and mend it later. Each change is queued and lands at the start of the next tick, all at once, so within a tick every enemy sees the same map. An enemy whose route used something that has gone notices and searches again.

Navigation is optional. A level with no map still has enemies; they steer straight at what they want, as simpler shooters did.

• Level machineryThe doors, lifts, ladders and portals the routes run through.
• How enemies decideWhere an enemy wants to go, and why.
• Player movementThe same world, crossed by the player.