Lightflow Question

(Skates) #1

Why does making the “kb” value on a material in lightflow increase the render times SO horribly? It increases it by maybe 100 times if you crank it up enough! There must be a reason, blurred refraction doesn’t come cheap of course, but really! that much?

(meestaplu) #2

All right Mr. Skates…

In a perfect reflection with one incident ray, only one reflected ray is generated. In a diffuse reflection, there are multiple reflected rays. Some of these rays are concentrated around one direction, resulting in a specular highlight. A blurred refraction is the same way – it could also be called a diffuse refraction. One ray becomes many in both cases.

A raytracer calculates the path that every ray takes (let’s not talk about forward and backward raytracing right now).

Thus, when blurred reflection and refraction is used, Lightflow has to calculate multiple refracted or reflected rays for every incident ray. These reflected rays become incident rays, and so on, until the number of interactions has reached the number specified by the trace depth parameter.