Rename World.Mask

This is a cosmetic change intended to establish a better vocabulary for describing ECS concepts. I think mask is very close and I don’t want to change it if there isn’t a significantly better name.

The problem that I see with mask is that the values of the World.Mask array are not used as masks. They’re bitfields (or bitsets) but they’re not used to mask other bitfields in Goodluck. Instead, systems define their masks (QUERY) to filter entities to run on. The semantic difference is marginal, but I’d like to spend some effort and try to find a better name which would better describe how these values are used.

[stasm]

I was reading up on ECS design in languages with manual memory managment, and I came across an article by Austin Morlan in which he used the term signature to describe exactly what the values of World.Mask are:

Since an entity is simply an ID, we need a way to track which components an entity “has”, and we also need a way to track which components a system cares about. I chose the very simple approach of using a std::bitset (modern C++ equivalent of a bitfield), called a Signature. Each component type has a unique ID (starting from 0), which is used to represent a bit in the signature.

I really like this name. It gives us a single word to precisely describe a concept in Goodluck. Instead of saying a bit mask describing the component composition of an entity, we can say: the entity’s signature.

[stasm]

I’m going to leave this open for a few more days in case I have more ideas. So far, I don’t think any of the alternatives is significantly better than Mask.