We are designing a new Rombo.PowerMetal material. At the moment it supports STD generalized distribution for microfaceting reflections, microfacet normal mapping, multi-bounce microfaceting for correct energy conservation and rombo adaptive sampling for hard to sample highlights.
STD distribution allow for both GGX(reflection slope set to 2) and Beckmann(set to 4) distributions and goes further on both ends, making reflection tails narrower than Beckmann(slope > 4) or more wide than GGX(slope < 2). The cool thing is that the parameter is texturable so one can account for positional variance of distribution slopes, ie one can map different distributions onto the same BRDF.
Microfacet normal mapping is a new cool feature that resolves all the artifact that comes with normal mapping. Generally you cannot increase way too much bump/normal depth because doing so artifacts will start to appear in the form of black fringes or the whole surface will just start appearing dry and kinda sucking all of the highlights. For example here a comparison between Arnold normal mapping (left) and Rombo normal mapping.
We support both true multi-scattering for microfacet reflections as well as an energy compensation term for faster renders. Here a comparison with Arnold (right, darker).
And here where we test it on a white furnace test. That means. For full energy preservation the outcomes must be fully white … as it is on the left rombo sphere.
Then take care that also normal/bump mapping tend to suck energy. Right Arnold, left Rombo multiscatter microfacet normal mapping.