Just as another example to look at, my MDL_renderer example supports cubic B-splines for hair rendering with MDL’s hair_bsdf() (Chiang model).
https://forums.developer.nvidia.com/t/optix-advanced-samples-on-github/48410/12
That example is using anyhit programs for shadow ray testing though because the renderer needs to support cutout opacity.
The rtigo10 example in the same repository is using faster shadow rays with OPTIX_RAY_FLAG_TERMINATE_ON_FIRST_HIT but that doesn’t have curve primitives.
But I’m also relying on the fact that OptiX curves are not hitting back faces and only use the scene epsilon to offset the continuation or shadow rays and that works fine:
https://github.com/NVIDIA/OptiX_Apps/blob/master/apps/MDL_renderer/shaders/hit.cu#L1501
https://github.com/NVIDIA/OptiX_Apps/blob/master/apps/MDL_renderer/shaders/raygeneration.cu#L132