TryRead/Write for querying optional components

[Ralith]

If this implementation strategy looks good, I'll follow up with a similar MaybeWrite.

[jaynus]

@AThilenius would this meet your needs for the problems we ran into in legion_transform and reduce a lot of that query boilerplate?

[AThilenius]

Yep, I could replace the dozen separate queries with this. It could still pick up invalid combinations like Scale + NonUniformScale, but throwing a runtime error ther is totally acceptable. Can this be done efficiently though? I'm on my phone so don't want to dig through code.

[Ralith]

Can this be done efficiently though? I'm on my phone so don't want to dig through code.

A query containing TryRead should cost about the same to execute as the same query with that field removed. It's significantly more efficient than calling get_component inside a query.

[jaynus]

It's significantly more efficient than calling get_component inside a query.

The solution currently in legion_transform is about 12 different queries for all variations, all iterating in parallel. I wonder if that is actually faster than this case still.

[TomGillen]

I expect performance would be similar (assuming you use par_for_each or equivalent), but the code would be vastly simplified.

[Ralith]

Added TryWrite along the same lines.