I've tried something like , but that doesn't work that well. Is there a better approximation?
I'm currently changing the BRDF to an actual Cook-Torrance BRDF with Trowbridge-Reitz distribution, Schlick fresnel and Smith-Trowbridge-Reitz geometry factor. The BRDF itself is only 27 clock cycles on a Fermi or Kepler GPU (NDotL, NDotH, LDotH, ... not included). It's fast enough, so there's no reason for me to use a weak approximation of Cook-Torrance. But all my models are still storing Blinn-Phong glossiness, that's why I need to convert them.
I actually would want to use an approximation for though. That's the worst part of the whole BRDF. The 2 square roots alone take 12 clock cycles
Edited by CryZe, 17 September 2012 - 08:38 AM.