Reorganized light and surface traits so that light sources are
surfaces as well, which will let them slide easily into
intersection tests with the rest of the scene geometry.
The lighting is super crappy, and pretty much hacked in. Will
need to redo this properly soon. However, this verifies that
certain other parts of the code are (mostly) working properly.
BVH traversal still happens in local space, but final actual
surface intersection calculations are done in world space by
transforming the triangle into world space. This is to improve
numerical consistency between intersections.
This is mainly just to make the tracer code read more cleanly.
All of the pushing and popping logic obscured the big picture
and made things a bit confusing.
The AssemblyBuilder is responsible for collecting the data needed
to actually create an Assembly. AssemblyBuilders are now the
only way to create an Assembly, which guarantees that Assemblies
aren't half-baked.
Also got instancing working with transforms and such. It may not
be _really_ working because I don't have a complex test case for
it yet. But that will come later.
Apparently this is what UnsafeCell is for, and the code I wrote
before wasn't technically correct, even thought it worked in
practice. Hooray for doing things properly!
Includes:
- More scene parsing code. Making good progress!
- Making the rendering code actually use the Scene and Assembly
types.
- Bare beginnings of a Tracer type.
