IOR limitations
We also need to support dielectric materials inside of dielectric materials (this could be recursive), for that we need to store a stack of iors in the per ray data structure (current_prd in cuda code). For now only one ior is store in the current_prd, which allows us to have a conductor object dielectric inside a dielectric one (see scene MRF_DIR/assets/scenes/torus_in_glass.msf). In fact, this current ior allows us to know that the ray is inside a dielectric when hitting the conductor, but when leaving the inside of the dielectric material we suppose we go back to the default ior of scene, the air, hence the need for a stack of iors.
This is a big issue but not easy to solve when wanting to take into account all possible cases