Customize entity ID selection

[klausenfeld]

I want to manually partition the entity ID space. I don't really care about generations for many of my entities. If I despawn an entity of ID X and re-create it later, I'm OK with re-using the same ID and reviving all references to it (which won't exist). Most importantly, I want to encode spacial coordinates into some of the ID space. I have a tiled map which should have an entity for each tile that's currently alive. If I could map spacial coordinates directly into the entity ID space, I could easily find neighbors to a given tile, without storing and managing explicit references.

Furthermore I have several sets of entities which I want to iterate in a stable order. That can be achieved by building a linked list on top of the entities using components, but that looks silly to me. I could just partition off a bit of ID space and choose consecutive IDs from that.

In more concrete terms, I want IDs that consist of maybe 4 bits of descriptor to encode the entity "category", and then either 28 or 60 bits of actual ID, depending on whether I want to use generations for those particular IDs or not. The 60 bits could be split into 20/20/20 for x/y/z on entities of category "tile". That should be enough for a long time. There will be a category "everything else". 15 special categories should be enough.

Now there is Entity::from_bits() and Commands::get_or_spawn(). These would probably be good enough for what I want. Both come with big bold warnings, though. Even Entity::from_raw() is apparently frowned upon and that would only give me 32 bits of ID space.

So, is this idea abhorrently evil? Is there a better way to achieve what I want?

[klausenfeld]

Well, @cart, I would really like to read your messages on discord. However, discord hates my mail server and I will not give it my phone number for validation since it will just become further material for its hatred. I only have one phone number ...

[klausenfeld]

This idea doesn't work because bevy generally wants to keep entity metadata in a vector, indexed by the entity index. Maybe I can add a translation table between my coordinates and the entity indices.