Refactor and revamp import and export of `UsdGeomNurbsCurves` prim
objects.
Fixes#130056, among other things.
Summary of changes and enhancements:
- Export:
- Write out `nurb_weight` attribute as the USD `pointWeights` primvar
- Properly write out cyclic NURBS curves data (* see notes)
- Import:
- Import using the new `Curves` datablock rather than the old `Curve`
- Properly read in cyclic NURBS curves data (* see notes)
- Tries harder to match incoming knot vector to standard `knots_mode`,
will use Custom otherwise
- Support import of all custom primvars and data attached to the prim
(for use with Geometry Nodes etc.) (* see notes)
Tests were added which check a variety of point count, order, knot_mode,
and cyclic combinations (generated through Geometry Nodes). A small
number of hand-crafted curves were used to test the Custom knots_mode
support on import. Additionally, the tests cover the case when there are
multiple curves defined for a single object.
Notes:
- Cyclic NURBS support is reliant on the current, under-spec'd, USD
documentation. Changes may be required in the future if/when the USD
spec is clarified: https://github.com/PixarAnimationStudios/OpenUSD/issues/3740
- Some Cyclic x knots_mode combinations are not correct and would
require more research to determine how to properly address.
- Custom attributes are not imported for Cyclic NURBS curves yet. Those
will require additional work to function correctly and are also
reliant on seeing how the USD spec changes.
Pull Request: https://projects.blender.org/blender/blender/pulls/143970
7111e95527