This is the beginning of adding ECS to QF. While the previous iteration
of hierarchies was a start in the direction towards ECS, this pulls most
of the 3d-specific transform stuff out of the hierarchy "objects",
making all the matrices and vectors/quaternions actual components (in
the ECS sense). There's more work to be done with respect to the
transform and entity members of hierarchy_t (entity should probably go
away entirely, and transform should become hierref_t (or whatever its
final name becomes), but I wanted to get things working sooner than
later.
The motivation for the effort was to allow views to use hierarchy_t,
which should be possible once I get entity and transform sorted out.
I am really glad I already had automated tests for hierarchies, as
things proved to be a little tricky to get working due to forgetting why
certain things were there.
It copies an entire hierarchy (minus actual entities, but I'm as yet
unsure how to proceed with them), even across scenes as the source scene
is irrelevant and the destination scene is used for creating the new
transforms.
The root transform of each hierarchy can be extracted from the first
transform of the list in the hierarchy, so no information is lost. The
main reason for the change is I discovered (obvious in hindsight) that
deleting root transforms was O(n) due to keeping them in an array, thus
the use of a linked list (I don't expect a hierarchy to be in more than
one such list), and I didn't want the transforms to be in a linked list.
Since transforms now know the scene to which they belong, and they know
when they are root and when not, getting the transform code to manage
the scene roots is the best way to keep the list of root transforms
consistent.
This actually has at least two benefits: the transform id is managed by
the scene and thus does not need separate management by the Ruamoko
wrapper functions, and better memory handling of the transform objects.
Another benefit that isn't realized yet is that this is a step towards
breaking the renderers free of quake and quakeworld: although the
clients don't actually use the scene yet, it will be a good place to
store the rendering information (functions to run, etc).
Holding onto the pointer is not a good idea, and it is read-only as
direct manipulation of the world matrix is not supported. However, this
is useful for passing the matrix to the GPU.
