From f4b61c696b740cf173d1ba7decc3f776955cf02b Mon Sep 17 00:00:00 2001 From: Lukas Stockner Date: Sun, 30 Oct 2022 00:14:03 +0200 Subject: Simplify v1 Fresnel computation --- intern/cycles/app/cycles_precompute.cpp | 2 +- intern/cycles/kernel/closure/bsdf_microfacet_util.h | 2 +- intern/cycles/kernel/closure/bsdf_util.h | 15 ++++++++++----- 3 files changed, 12 insertions(+), 7 deletions(-) diff --git a/intern/cycles/app/cycles_precompute.cpp b/intern/cycles/app/cycles_precompute.cpp index 6f9d9601b1e..b55246e9e91 100644 --- a/intern/cycles/app/cycles_precompute.cpp +++ b/intern/cycles/app/cycles_precompute.cpp @@ -213,7 +213,7 @@ static float precompute_ggx_dielectric_E(float rough, float mu, float eta, float * is an issue since there are changes in that range at higher roughnesses. * Therefore, the remapping is blended with the identity function for a compromise. */ - float F0 = fresnel_dielectric_cos(1.0f, eta); + float F0 = fresnel_dielectric_F0(eta); auto get_remap = [eta, F0](float x) { return mix(x, inverse_lerp(1.0f, F0, fresnel_dielectric_cos(x, eta)), 0.5f); }; diff --git a/intern/cycles/kernel/closure/bsdf_microfacet_util.h b/intern/cycles/kernel/closure/bsdf_microfacet_util.h index b531c192e03..8a0902f054b 100644 --- a/intern/cycles/kernel/closure/bsdf_microfacet_util.h +++ b/intern/cycles/kernel/closure/bsdf_microfacet_util.h @@ -106,7 +106,7 @@ ccl_device_forceinline float microfacet_ggx_dielectric_E(KernelGlobals kg, kernel_data.tables.ggx_dielectric_E_offset; float macro_fresnel = fresnel_dielectric_cos(mu, ior); - float F0 = fresnel_dielectric_cos(1.0f, ior); + float F0 = fresnel_dielectric_F0(ior); float x = mix(mu, inverse_lerp(1.0f, F0, macro_fresnel), 0.5f); float y = 1 - rough; float z = sqrtf(0.5f * ((inv_table ? 1.0f / ior : ior) - 1.0f)); diff --git a/intern/cycles/kernel/closure/bsdf_util.h b/intern/cycles/kernel/closure/bsdf_util.h index 13de4ac15b0..47a37a43c87 100644 --- a/intern/cycles/kernel/closure/bsdf_util.h +++ b/intern/cycles/kernel/closure/bsdf_util.h @@ -71,6 +71,13 @@ ccl_device float fresnel_dielectric_cos(float cosi, float eta) return 1.0f; // TIR(no refracted component) } +/* Returns F0 (perpendicular) reflectivity for given eta, + * equivalent to fresnel_dielectric_cos(1.0f, eta). */ +ccl_device float fresnel_dielectric_F0(float eta) +{ + return sqr((eta - 1.0f) / (eta + 1.0f)); +} + ccl_device Spectrum fresnel_conductor(float cosi, const Spectrum eta, const Spectrum k) { Spectrum cosi2 = make_spectrum(sqr(cosi)); @@ -124,11 +131,9 @@ ccl_device_forceinline Spectrum interpolate_fresnel_color(Spectrum L, { /* Compute the real Fresnel term and remap it from real_F0...1 to F0...1. * We could also just use actual Schlick fresnel (mix(F0, 1, (1-cosI)^5)) here. */ - float real_F0 = fresnel_dielectric_cos(1.0f, ior); - float F0_norm = 1.0f / (1.0f - real_F0); - float FH = (fresnel_dielectric_cos(dot(L, H), ior) - real_F0) * F0_norm; - - return mix(F0, one_spectrum(), FH); + float real_F0 = fresnel_dielectric_F0(ior); + float mixFactor = inverse_lerp(real_F0, 1.0f, fresnel_dielectric_cos(dot(L, H), ior)); + return mix(F0, one_spectrum(), mixFactor); } ccl_device float3 ensure_valid_reflection(float3 Ng, float3 I, float3 N) -- cgit v1.2.3