[ f_r = f_diffuse + f_specular ] For perfectly rough surfaces, V-Ray defaults to the Lambertian model (constant albedo). However, for rough, clay-like materials, V-Ray implements the Oren-Nayar model, which accounts for retro-reflection:
[ L_o(\omega_o) = \int_\Omega f_r(\omega_i, \omega_o) L_i(\omega_i) (n \cdot \omega_i) d\omega_i ] vray materials
[ \mathbbV[L] \propto \frac1N \sum_k=1^N \fracf(\omega_k)p(\omega_k) \cdot \texttrunc_L(\textFTT(u,v)) ] [ f_r = f_diffuse + f_specular ] For
Where ( f_r ) is the VRay BRDF kernel, decomposed into diffuse and specular lobes: V-Ray implements the Oren-Nayar model
[ G_Smith(l,v) = \chi^+ \left( \frac2 (n \cdot l)(n \cdot v)(n \cdot v) \sqrt\alpha^2 + (1-\alpha^2)(n \cdot l)^2 + (n \cdot l) \sqrt\alpha^2 + (1-\alpha^2)(n \cdot v)^2 \right) ] V-Ray distinguishes materials via the Fresnel equation , not a binary metallic flag. For dielectrics (glass, wood, plastic):
A Comprehensive Analysis of V-Ray Material Models: Physically-Based Rendering, BRDF Microfacet Theory, and Stochastic Texture Evaluation
[ S(x_i, \omega_i; x_o, \omega_o) = F(\eta, \omega_i) R_d(|x_i - x_o|) F(\eta, \omega_o) ]