Speeding trough the Rainbow-Tunnel

Concept

Volumetric rendering refers to the concept (at least in raytracing) of not intersectiong with an object and be done with it, but instead calculate the light-medium interaction for a distance d the ray travels while in said medium. This allows for many astounding and realistic image effects, like fog, god-rays, clouds, you name it. The Mediums are generally split into heterogen (varying properties) and homogen (constant properties)

We implement Volume rendering by allowing arbitrary primitives to encompass a medium. When we intersect with such a primitive, instead of stopping, we continue in the direction indicated by the material of the primitive. We will then intersect a shape or the end of the medium. iIn either case, we calculate the mediums properties (absorption, out-scattering, in-scattering, emission) for the distance traveled in the medium. We achieve this by approximation the necessary integral by quadrature, i.e. by sampling the properties at an finite amount of points, and summing up. If we intersect a shape, we then calculate the total lightning, if not we repeat this process until we do (We assume that there are no "infinite" mediums, since they are not only physically impossible, the also don't add much over just regular very big mediums)
We use this to create the god-ray like effect of the rainbow by filling the tunnel with a medium with high in-scattering properties.