Yocto/GL
Yocto/GL: Tiny C++ Libraries for Data-Driven Physically-based Graphics
...Simple shape data structure, utilities for manipulating triangle meshes, quads meshes and line sets, computation of normals and tangents, linear and Catmull-Clark subdivision, procedural shapes generation, ray intersection and closest point queries. Ray intersection and closest point queries of triangle meshes, quads meshes, line sets and shape instances using a two-level bounding volume hierarchy. Path tracing of surfaces and hairs supporting area and environment illumination, microfacet GGX and subsurface scattering, multiple importance sampling.