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.
This means that the component id used for hierarchy references must be
passed to Hierarchy_New and Hierarchy_Copy, but does all an entity to
have more than one hierarchy, which is useful for canvases (hierarchies
of views) in the 3d world (the canvas root would have a 3d hierarchy
reference and a 2d (view) hierarchy reference).
While simple component pools can be cleared simply by zeroing their
counts, ones that have a delete function need that function to be called
for all the components in the pool otherwise leaks can happen.
It should have always been here, but when I first created the hierarchy
and transform objects, I didn't know where things would go. Having two
chunks of code for setting an entity's parent was too already too much,
and I expect to have other hierarchy types. Doesn't fix the issues
encountered with sbar, of course.
As the bookkeeping data is spread between three arrays, sorting a
component pool is not trivial and thus not something to duplicate around
the codebase.
It doesn't check that the entity itself is valid, but it does at least
check that the index fetched from the sparse array is valid. Fixes a
segfault when a valid entity never had the component.
While the libraries are probably getting a little out of hand, the
separation into its own directory is probably a good thing as an ECS
should not be tied to scenes. This should make the ECS more generally
useful.
