Examples of branching. This will probably need recursion via functions (or an explicit stack some other way).
I need to figure out winding order. It is consistent through seemingly everything, except for reflection and close_boundary_simple. (When there are two parallel boundaries joined with something like join_boundary_simple, traversing these boundaries in their actual order to generate triangles - like in close_boundary_simple - will produce opposite winding order on each. Imagine a transparent clock: seen from the front, it moves clockwise, but seen from the back, it moves counter-clockwise.)
Make it easier to build up meshes a bit at a time?
Factor out recursive/iterative stuff to be a bit more concise
Embed this in Blender?
File that bug that I've seen in trimesh/three.js (see trimesh_fail.ipynb)
Parametrize gen_twisted_boundary over boundaries and do my nested spiral
Why do I get the weird zig-zag pattern on the triangles, despite larger numbers of them? Is it something in how I twist the frames?
- How can I compute the torsion on a quad? I think it comes down to this: torsion applied across the quad I'm triangulating leading to neither diagonal being a particularly good choice. Subdividing the boundary seems to help, but other triangulation methods (e.g. turning a quad to 4 triangles by adding the centroid) could be good too.
- Facets/edges are just oriented the wrong way...
I need an actual example of branching/forking. If I simply split a boundary into sub-boundaries per the rules I already have in my notes, then this still lets me split any way I want to without having to worry about joining N boundaries instead of 2, doesn't it?

Other notes:

Picking at random the diagonal on the quad to triangulate with does seem to turn 'error' just to noise, and in its own way this is preferable.

Abstractions

Encode the notions of "generator which transforms an existing list of boundaries", "generator which transforms another generator"
This has a lot of functions parametrized over a lot of functions. Need to work with this somehow. (e.g. should it subdivide this boundary? should it merge opening/closing boundaries?)
Work directly with lists of boundaries. The only thing I ever do with them is apply transforms to all of them, or join adjacent ones with corresponding elements.