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Optimizations to GLSL FresnelData #1733

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Mar 10, 2024
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Optimizations to GLSL FresnelData #1733

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144 changes: 47 additions & 97 deletions libraries/pbrlib/genglsl/lib/mx_microfacet_specular.glsl
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Original file line number Diff line number Diff line change
@@ -1,16 +1,15 @@
#include "mx_microfacet.glsl"

// Fresnel model options.
const int FRESNEL_MODEL_DIELECTRIC = 0;
const int FRESNEL_MODEL_CONDUCTOR = 1;
const int FRESNEL_MODEL_SCHLICK = 2;
const int FRESNEL_MODEL_AIRY = 3;
const int FRESNEL_MODEL_SCHLICK_AIRY = 4;

// Parameters for Fresnel calculations.
// Parameters for Fresnel calculations
struct FresnelData
{
// Fresnel model
int model;
bool airy;

// Physical Fresnel
vec3 ior;
Expand All @@ -28,32 +27,6 @@ struct FresnelData

// Refraction
bool refraction;

#ifdef __METAL__
FresnelData(int _model = 0,
vec3 _ior = vec3(0.0f),
vec3 _extinction = vec3(0.0f),
vec3 _F0 = vec3(0.0f),
vec3 _F82 = vec3(0.0f),
vec3 _F90 = vec3(0.0f),
float _exponent = 0.0f,
float _tf_thickness = 0.0f,
float _tf_ior = 0.0f,
bool _refraction = false) :
model(_model),
ior(_ior),
extinction(_extinction),
F0(_F0),
F82(_F82),
F90(_F90),
exponent(_exponent),
tf_thickness(_tf_thickness),
tf_ior(_tf_ior),
refraction(_refraction)
{
}
#endif

};

// https://media.disneyanimation.com/uploads/production/publication_asset/48/asset/s2012_pbs_disney_brdf_notes_v3.pdf
Expand Down Expand Up @@ -225,7 +198,6 @@ float mx_f0_to_ior(float F0)
float sqrtF0 = sqrt(clamp(F0, 0.01, 0.99));
return (1.0 + sqrtF0) / (1.0 - sqrtF0);
}

vec3 mx_f0_to_ior(vec3 F0)
{
vec3 sqrtF0 = sqrt(clamp(F0, 0.01, 0.99));
Expand Down Expand Up @@ -269,14 +241,7 @@ float mx_fresnel_dielectric(float cosTheta, float ior)

void mx_fresnel_dielectric_polarized(float cosTheta, float ior, out float Rp, out float Rs)
{
if (cosTheta < 0.0)
{
Rp = 1.0;
Rs = 1.0;
return;
}

float cosTheta2 = cosTheta * cosTheta;
float cosTheta2 = mx_square(clamp(cosTheta, 0.0, 1.0));
float sinTheta2 = 1.0 - cosTheta2;

float t0 = max(ior * ior - sinTheta2, 0.0);
Expand Down Expand Up @@ -375,17 +340,14 @@ vec3 mx_fresnel_airy(float cosTheta, FresnelData fd)
// XYZ to CIE 1931 RGB color space (using neutral E illuminant)
const mat3 XYZ_TO_RGB = mat3(2.3706743, -0.5138850, 0.0052982, -0.9000405, 1.4253036, -0.0146949, -0.4706338, 0.0885814, 1.0093968);

// Select between Schlick and physical models.
bool useSchlickAiry = fd.model == FRESNEL_MODEL_SCHLICK_AIRY;

// Convert nm -> m
float d = fd.tf_thickness * 1.0e-9;

// Assume vacuum on the outside
float eta1 = 1.0;
float eta2 = max(fd.tf_ior, eta1);
vec3 eta3 = useSchlickAiry ? mx_f0_to_ior(fd.F0) : fd.ior;
vec3 kappa3 = useSchlickAiry ? vec3(0.0) : fd.extinction;
vec3 eta3 = (fd.model == FRESNEL_MODEL_SCHLICK) ? mx_f0_to_ior(fd.F0) : fd.ior;
vec3 kappa3 = (fd.model == FRESNEL_MODEL_SCHLICK) ? vec3(0.0) : fd.extinction;

// Compute the Spectral versions of the Fresnel reflectance and
// transmitance for each interface.
Expand All @@ -399,7 +361,7 @@ vec3 mx_fresnel_airy(float cosTheta, FresnelData fd)
float scale = eta1 / eta2;
float cosThetaTSqr = 1.0 - (1.0-cosTheta*cosTheta) * scale*scale;
float cosTheta2 = sqrt(cosThetaTSqr);
if (useSchlickAiry)
if (fd.model == FRESNEL_MODEL_SCHLICK)
{
vec3 f = mx_fresnel_hoffman_schlick(cosTheta2, fd);
R23p = 0.5 * f;
Expand Down Expand Up @@ -429,7 +391,7 @@ vec3 mx_fresnel_airy(float cosTheta, FresnelData fd)

// Evaluate the phase shift
mx_fresnel_dielectric_phase_polarized(cosTheta, eta1, eta2, phi21p, phi21s);
if (useSchlickAiry)
if (fd.model == FRESNEL_MODEL_SCHLICK)
{
phi23p = vec3((eta3[0] < eta2) ? M_PI : 0.0,
(eta3[1] < eta2) ? M_PI : 0.0,
Expand All @@ -449,14 +411,13 @@ vec3 mx_fresnel_airy(float cosTheta, FresnelData fd)

// Evaluate iridescence term
vec3 I = vec3(0.0);
vec3 C0, Cm, Sm;
vec3 Cm, Sm;

// Iridescence term using spectral antialiasing for Parallel polarization

// Reflectance term for m=0 (DC term amplitude)
vec3 Rs = (T121p*T121p*R23p) / (vec3(1.0) - R12p*R23p);
C0 = R12p + Rs;
I += C0;
I += R12p + Rs;

// Reflectance term for m>0 (pairs of diracs)
Cm = Rs - T121p;
Expand All @@ -471,8 +432,7 @@ vec3 mx_fresnel_airy(float cosTheta, FresnelData fd)

// Reflectance term for m=0 (DC term amplitude)
vec3 Rp = (T121s*T121s*R23s) / (vec3(1.0) - R12s*R23s);
C0 = R12s + Rp;
I += C0;
I += R12s + Rp;

// Reflectance term for m>0 (pairs of diracs)
Cm = Rp - T121s;
Expand All @@ -492,84 +452,74 @@ vec3 mx_fresnel_airy(float cosTheta, FresnelData fd)
return I;
}

FresnelData mx_init_fresnel_data(int model)
FresnelData mx_init_fresnel_dielectric(float ior, float tf_thickness, float tf_ior)
{
return FresnelData(model, vec3(0.0), vec3(0.0), vec3(0.0), vec3(0.0), vec3(0.0), 0.0, 0.0, 0.0, false);
}

FresnelData mx_init_fresnel_dielectric(float ior)
{
FresnelData fd = mx_init_fresnel_data(FRESNEL_MODEL_DIELECTRIC);
FresnelData fd;
fd.model = FRESNEL_MODEL_DIELECTRIC;
fd.airy = tf_thickness > 0.0;
fd.ior = vec3(ior);
fd.extinction = vec3(0.0);
fd.F0 = vec3(0.0);
fd.F82 = vec3(0.0);
fd.F90 = vec3(0.0);
fd.exponent = 0.0;
fd.tf_thickness = tf_thickness;
fd.tf_ior = tf_ior;
fd.refraction = false;
return fd;
}

FresnelData mx_init_fresnel_conductor(vec3 ior, vec3 extinction)
FresnelData mx_init_fresnel_conductor(vec3 ior, vec3 extinction, float tf_thickness, float tf_ior)
{
FresnelData fd = mx_init_fresnel_data(FRESNEL_MODEL_CONDUCTOR);
FresnelData fd;
fd.model = FRESNEL_MODEL_CONDUCTOR;
fd.airy = tf_thickness > 0.0;
fd.ior = ior;
fd.extinction = extinction;
fd.F0 = vec3(0.0);
fd.F82 = vec3(0.0);
fd.F90 = vec3(0.0);
fd.exponent = 0.0;
fd.tf_thickness = tf_thickness;
fd.tf_ior = tf_ior;
fd.refraction = false;
return fd;
}

FresnelData mx_init_fresnel_schlick(vec3 F0, vec3 F82, vec3 F90, float exponent)
{
FresnelData fd = mx_init_fresnel_data(FRESNEL_MODEL_SCHLICK);
fd.F0 = F0;
fd.F82 = F82;
fd.F90 = F90;
fd.exponent = exponent;
return fd;
}

FresnelData mx_init_fresnel_schlick_airy(vec3 F0, vec3 F82, vec3 F90, float exponent, float tf_thickness, float tf_ior)
FresnelData mx_init_fresnel_schlick(vec3 F0, vec3 F82, vec3 F90, float exponent, float tf_thickness, float tf_ior)
{
FresnelData fd = mx_init_fresnel_data(FRESNEL_MODEL_SCHLICK_AIRY);
FresnelData fd;
fd.model = FRESNEL_MODEL_SCHLICK;
fd.airy = tf_thickness > 0.0;
fd.ior = vec3(0.0);
fd.extinction = vec3(0.0);
fd.F0 = F0;
fd.F82 = F82;
fd.F90 = F90;
fd.exponent = exponent;
fd.tf_thickness = tf_thickness;
fd.tf_ior = tf_ior;
return fd;
}

FresnelData mx_init_fresnel_dielectric_airy(float ior, float tf_thickness, float tf_ior)
{
FresnelData fd = mx_init_fresnel_data(FRESNEL_MODEL_AIRY);
fd.ior = vec3(ior);
fd.tf_thickness = tf_thickness;
fd.tf_ior = tf_ior;
return fd;
}

FresnelData mx_init_fresnel_conductor_airy(vec3 ior, vec3 extinction, float tf_thickness, float tf_ior)
{
FresnelData fd = mx_init_fresnel_data(FRESNEL_MODEL_AIRY);
fd.ior = ior;
fd.extinction = extinction;
fd.tf_thickness = tf_thickness;
fd.tf_ior = tf_ior;
fd.refraction = false;
return fd;
}

vec3 mx_compute_fresnel(float cosTheta, FresnelData fd)
{
if (fd.model == FRESNEL_MODEL_DIELECTRIC)
if (fd.airy)
{
return mx_fresnel_airy(cosTheta, fd);
}
else if (fd.model == FRESNEL_MODEL_DIELECTRIC)
{
return vec3(mx_fresnel_dielectric(cosTheta, fd.ior.x));
}
else if (fd.model == FRESNEL_MODEL_CONDUCTOR)
{
return mx_fresnel_conductor(cosTheta, fd.ior, fd.extinction);
}
else if (fd.model == FRESNEL_MODEL_SCHLICK)
{
return mx_fresnel_hoffman_schlick(cosTheta, fd);
}
else
{
return mx_fresnel_airy(cosTheta, fd);
return mx_fresnel_hoffman_schlick(cosTheta, fd);
}
}

Expand Down
14 changes: 2 additions & 12 deletions libraries/pbrlib/genglsl/mx_conductor_bsdf.glsl
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Original file line number Diff line number Diff line change
Expand Up @@ -23,12 +23,7 @@ void mx_conductor_bsdf_reflection(vec3 L, vec3 V, vec3 P, float occlusion, float
float avgAlpha = mx_average_alpha(safeAlpha);
vec3 Ht = vec3(dot(H, X), dot(H, Y), dot(H, N));

FresnelData fd;
if (thinfilm_thickness > 0.0)
fd = mx_init_fresnel_conductor_airy(ior_n, ior_k, thinfilm_thickness, thinfilm_ior);
else
fd = mx_init_fresnel_conductor(ior_n, ior_k);

FresnelData fd = mx_init_fresnel_conductor(ior_n, ior_k, thinfilm_thickness, thinfilm_ior);
vec3 F = mx_compute_fresnel(VdotH, fd);
float D = mx_ggx_NDF(Ht, safeAlpha);
float G = mx_ggx_smith_G2(NdotL, NdotV, avgAlpha);
Expand All @@ -52,12 +47,7 @@ void mx_conductor_bsdf_indirect(vec3 V, float weight, vec3 ior_n, vec3 ior_k, ve

float NdotV = clamp(dot(N, V), M_FLOAT_EPS, 1.0);

FresnelData fd;
if (thinfilm_thickness > 0.0)
fd = mx_init_fresnel_conductor_airy(ior_n, ior_k, thinfilm_thickness, thinfilm_ior);
else
fd = mx_init_fresnel_conductor(ior_n, ior_k);

FresnelData fd = mx_init_fresnel_conductor(ior_n, ior_k, thinfilm_thickness, thinfilm_ior);
vec3 F = mx_compute_fresnel(NdotV, fd);

vec2 safeAlpha = clamp(roughness, M_FLOAT_EPS, 1.0);
Expand Down
30 changes: 3 additions & 27 deletions libraries/pbrlib/genglsl/mx_dielectric_bsdf.glsl
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Original file line number Diff line number Diff line change
Expand Up @@ -21,16 +21,8 @@ void mx_dielectric_bsdf_reflection(vec3 L, vec3 V, vec3 P, float occlusion, floa
float avgAlpha = mx_average_alpha(safeAlpha);
vec3 Ht = vec3(dot(H, X), dot(H, Y), dot(H, N));

FresnelData fd;
vec3 safeTint = max(tint, 0.0);
if (thinfilm_thickness > 0.0)
{
fd = mx_init_fresnel_dielectric_airy(ior, thinfilm_thickness, thinfilm_ior);
}
else
{
fd = mx_init_fresnel_dielectric(ior);
}
FresnelData fd = mx_init_fresnel_dielectric(ior, thinfilm_thickness, thinfilm_ior);
vec3 F = mx_compute_fresnel(VdotH, fd);
float D = mx_ggx_NDF(Ht, safeAlpha);
float G = mx_ggx_smith_G2(NdotL, NdotV, avgAlpha);
Expand All @@ -54,16 +46,8 @@ void mx_dielectric_bsdf_transmission(vec3 V, float weight, vec3 tint, float ior,
N = mx_forward_facing_normal(N, V);
float NdotV = clamp(dot(N, V), M_FLOAT_EPS, 1.0);

FresnelData fd;
vec3 safeTint = max(tint, 0.0);
if (thinfilm_thickness > 0.0)
{
fd = mx_init_fresnel_dielectric_airy(ior, thinfilm_thickness, thinfilm_ior);
}
else
{
fd = mx_init_fresnel_dielectric(ior);
}
FresnelData fd = mx_init_fresnel_dielectric(ior, thinfilm_thickness, thinfilm_ior);
vec3 F = mx_compute_fresnel(NdotV, fd);

vec2 safeAlpha = clamp(roughness, M_FLOAT_EPS, 1.0);
Expand Down Expand Up @@ -91,16 +75,8 @@ void mx_dielectric_bsdf_indirect(vec3 V, float weight, vec3 tint, float ior, vec

float NdotV = clamp(dot(N, V), M_FLOAT_EPS, 1.0);

FresnelData fd;
vec3 safeTint = max(tint, 0.0);
if (thinfilm_thickness > 0.0)
{
fd = mx_init_fresnel_dielectric_airy(ior, thinfilm_thickness, thinfilm_ior);
}
else
{
fd = mx_init_fresnel_dielectric(ior);
}
FresnelData fd = mx_init_fresnel_dielectric(ior, thinfilm_thickness, thinfilm_ior);
vec3 F = mx_compute_fresnel(NdotV, fd);

vec2 safeAlpha = clamp(roughness, M_FLOAT_EPS, 1.0);
Expand Down
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