Be robust to unusual (but possible) case of (wi+wo)==Vector(0,0,0) in various halfangle BRDF code.
Be robust to unusual (but possible) case of (wi+wo)==Vector(0,0,0) in various halfangle BRDF code.
patwonder/pbrt-v2-skin,patwonder/pbrt-v2-skin,patwonder/pbrt-v2-skin,patwonder/pbrt-v2-skin,patwonder/pbrt-v2-skin