http://cseweb.ucsd.edu/~ravir/glints.pdf\

Specular BRDF rendering traditionally approximates surface microstructureusing a smooth normal distribution, but this ignoresglinty effects, easily observable in the real world. While modelingthe actual surface microstructure is possible, the resulting renderingproblem is prohibitively expensive. Recently, Yan et al. [2014]and Jakob et al. [2014] made progress on this problem, but theirapproaches are still expensive and lack full generality in their materialand illumination support. We introduce an efficient and generalmethod that can be easily integrated in a standard rendering system.We treat a specular surface as a four-dimensional position-normaldistribution, and fit this distribution using millions of 4D Gaussians,which we call elements. This leads to closed-form solutions to therequired BRDF evaluation and sampling queries, enabling the firstpractical solution to rendering specular microstructure