I'm not sure just what was going on other than *other* components were
getting double-removed when the hierarchy reference component was
removed when the entity was being deleted. This might even prevent
issues with removing the hierarchy from an entity that's not being
deleted as the pre-invalidation prevents the removal from deleting the
entity.
It turns out that the fixes for other problems related to removing
hierarchy reference components fixed the problem moving the entity
invalidation fixed, and invalidating the entity late somehow broke the
sprite renderer (at least in glsl).
The hierarchy leak was particularly troublesome to fix, but now the
hierarchies get updated (and freed) automatically just by removing the
hierarchy reference component from the entity. I suspect there will be
issues with entities that are on multiple hierarchies, but I'll sort
that out later.
Subpools are for grouping components by some criterion. Any component
that has a rangeid callback will be grouped with other components that
return the same render id. Note that the ordering of components within a
group will be affected by adding a component into a group that comes
before that group (or removing a component).
Component pools can have multiple groups, added and removed dynamically,
but removing a group should (currently) be done only when empty.
While this does require an extra call after registering components, it
allows for multiple component sets (ie, sub-systems) to be registered
before the component pools are created. The base id for the registered
component set is returned so it can be passed to the subsystem as
needed.
There's now a main ecs.h file that includes the sub-system headers,
removing the need to explicitly include several header files, but the
sub-systems are a less cluttered.
