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"Awareness" refers to an entity's view of the surrounding world with regards to how the entity could navigate. We use Recast/Detour to build a navmesh for the entity. However, since each world can have many NPCs, each one with their own mind, we don't want to keep a complete navmesh for each single mind. This will quickly become expensive. Therefore we want to share awarenesses between multiple entities of the same type. So, for example, all fishes handled by the same ai client will share one single awareness of the world. This to some degree involves some cheating, since AI minds now might get knowledge of the world they otherwise wouldn't have. We consider this to not be such a big issue. If this is unacceptable for some worlds these should then disable awareness sharing and take the resource hit.
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Movements and sights
Movement and sights are determined through a couple of rules and concepts. This document aims to explain how it works.
Domain
Each entity can have a Domain instance attached to it. The Domain determines both how contained things are allowed to move, and how sights are calculated. Only the entities directly contained in the Entity are considered.
Contained entities
When calculating movement and collisions for an entity, only entities belonging to the same Domain (i.e. those that have the same parent entity) are considered. Consider this example:
A World entity contains a Human and a Chest. The Chest in turn contains a Helmet. When the Human moves, collision detection is only carried out between the Human and the Chest, and never between the Human and the Helmet.
When calculating sights, each Domain must be queried in order. So, building on our previous example, if the Human sends a Look op to the Helmet, sight is determined by first checking with the World's domain if the Human can see the Chest. If this is allowed, the Chest's Domain is then queried if the Human is allowed to see the Helmet. If the Chest didn't have a Domain attached this wouldn't be allowed at all. If it has a Domain this can for example be a "chest" domain which first checks the open/closed state of the Chest, and then checks the distance of the Human from itself.
Note that the movement rules means that any entities that are expected to interact with one other physically must belong to the same world. So, consider an open crate entity. If items are to freely be put into the crate and then be able to interact with the world (i.e. falling out if the open crate is tipped) they must all belong to the same parent as the open crate itself. However, if items are to be stuck to the open crate, and not be able to interact with the world in any way, they should instead be entities contained by the crate.
Physical domain
The PhysicalDomain class is used for top level worlds. This kind of domain does all of the heavy lifting in the simulation. It knows how to handle the Terrain property and how to apply physical rules to the entities.
The standard physical rules that applies to the real world also applies to the Physical Domain.
Inventory domain
Any character which has an inventory can expose this through the Inventory Domain. No physical rules are applied to contained entities: velocity is ignored and no collision detection occurs. When an outside entity looks as an entity contained in the Inventory Domain sight is determined by checking if the entity is outiftted. I.e. if the entity in question has been registered in the Outfit property. Only those entities that are outfitted are visible to outside entities.
Container domain
Used for any container such as a chest, barrel or crate. Entities are physically constrained to the size of the container, and physics applies, but velocity is ignored. I.e. things are arranged, but nothing moves. Sights are determined both by checking the closed/open state of the container, and by checking the distance to the observing entity. Only entities standing close to the container should be able to look into it.
Custom domains
Apart from these domains there's room for more specialized ones, such as an "endless bag".