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#ifndef __BRDF_INC
#define __BRDF_INC
#include "pema99.cginc"
#include "pbr.cginc"
#include "lighting.cginc"
#include "lysenko.cginc"
#include "math.cginc"
float pow5(float x) {
float x2 = x * x;
return x2 * x2 * x;
}
float Fd_Lambertian(float NoL) {
return NoL;
}
// Schlick "An Inexpensive BRDF Model for Physically-based Rendering".
// Equation 24.
// f0: Reflectance at normal incidence. Typically around 0.04.
// f90: Reflectance at grazing incidence. Typically around 1.0.
float F_Schlick(float LoH, float f0, float f90) {
float term5 = pow5(1.0f - LoH);
return f0 + (f90 - f0) * term5;
}
float3 F_Schlick(float LoH, float3 f0, float f90) {
float term5 = pow5(1.0f - LoH);
float3 f90v = float3(f90, f90, f90);
return f0 + (f90v - f0) * term5;
}
// Walter "Microfacet Models for Refraction through Rough Surfaces"
// Equation 33.
// In the paper:
// - m = microsurface normal
// - n = macrosurface normal
// - theta_m = angle between micro- & macrosurface normals
// - alpha = roughness
// - cos(theta_m) = NoH
// Per sohcahtoa:
// tan(theta) = sin(theta) / cos(theta)
// tan^2(theta) = sin^2(theta) / cos^2(theta)
// = (1 - cos^2(theta)) / cos^2(theta)
// = -1 + 1 / cos^2(theta)
float D_GGX(float roughness, float NoH) {
float r2 = roughness * roughness;
float NoH2 = NoH * NoH;
float NoH4 = NoH2 * NoH2;
float k = rcp(NoH2) - 1;
float r2_plus_k = r2 + k;
float denom = NoH4 * r2_plus_k * r2_plus_k;
return r2 / denom;
}
// Hammon "PBR Diffuse Lighting for GGX+Smith Microsurfaces"
// Slide 84. Note that we remove the (4 * NoL * NoV) from the
// denominator of the specular lobe because of some cancellations.
// The original, un-optimized equation is:
// 2 * NoL * NoV / lerp(2 * NoL * NoV, NoL + NoV, roughness)
float G_GGXSmith(float roughness, float NoL, float NoV) {
float denom = 2.0f * lerp(2.0f * NoL * NoV, NoL + NoV, roughness);
return rcp(denom);
}
float4 brdf(Pbr pbr, LightData data) {
float3 specular = 0;
float3 diffuse = 0;
float f0 = 0.04f;
const float f90 = 1.0f;
//#define FURNACE_TEST_DIRECT
#if defined(FURNACE_TEST_DIRECT)
// Create the conditions for the standard BRDF furnace test.
// Only applies to the direct lighting stage. The only variable left over is
// NoV.
f0 = 1;
data.direct.color = 1;
data.direct.NoL = 1;
data.direct.NoH = 1;
data.direct.LoH = 1;
#endif
float2 dfg_uv = float2(data.common.NoV, pbr.roughness_perceptual);
float3 dfg;
[branch]
if (textureExists(_DFG_LUT)) {
dfg = _DFG_LUT.SampleLevel(bilinear_clamp_s, dfg_uv, 0).rgb;
} else {
dfg = float3(1, 1, 1);
}
#if defined(_CLEARCOAT)
const float cc_f0 = 0.04f;
float cc_perceptual_roughness = saturate(sqrt(pbr.cc_roughness));
float2 cc_dfg_uv = float2(data.common.NoV_cc, cc_perceptual_roughness);
float3 cc_dfg;
[branch]
if (textureExists(_DFG_LUT)) {
cc_dfg = _DFG_LUT.SampleLevel(bilinear_clamp_s, cc_dfg_uv, 0).rgb;
} else {
cc_dfg = float3(1, 1, 1);
}
float cc_Ess = max(cc_dfg.y, 1e-4f);
//float cc_energy_comp = 1.0f + cc_f0 * (rcp(cc_Ess) - 1.0f);
float cc_energy_comp = 1;
#endif
float3 f0_color = lerp(f0, pbr.albedo.xyz, pbr.metallic);
//float3 energy_comp = 1.0f + f0_color * (rcp(dfg.yyy) - 1.0f);
float3 energy_comp = 1.0f;
// Direct
{
float3 remainder = 1.0f;
#if defined(_CLEARCOAT)
float Fcc = F_Schlick(data.direct.LoH, cc_f0, f90);
float Dcc = D_GGX(pbr.cc_roughness, data.direct.NoH_cc);
float Gcc = G_GGXSmith(pbr.cc_roughness, data.direct.NoL_cc, data.common.NoV_cc);
float DFGcc = Fcc * Dcc * Gcc;
float3 direct_specular_cc = DFGcc * data.direct.color * data.direct.NoL_cc * pbr.cc_strength;
direct_specular_cc *= cc_energy_comp;
direct_specular_cc *= remainder;
direct_specular_cc = max(0, direct_specular_cc);
specular += direct_specular_cc;
remainder *= saturate(1.0f - Fcc * pbr.cc_strength);
#endif
float3 F = F_Schlick(data.direct.LoH, f0_color, f90);
float D = D_GGX(pbr.roughness, data.direct.NoH);
float G = G_GGXSmith(pbr.roughness, data.direct.NoL, data.common.NoV);
float3 direct_specular = (D * G) * F;
direct_specular *= data.direct.color * data.direct.NoL;
direct_specular *= energy_comp;
direct_specular *= remainder;
direct_specular = max(0, direct_specular);
specular += direct_specular;
#if defined(F_OREN_NAYAR)
float Fd = Fd_OrenNayar(pbr.roughness, data.common.NoV, data.direct.NoL, data.direct.LoV);
#else
float Fd = Fd_Lambertian(data.direct.NoL);
#endif
float3 direct_diffuse = Fd * (1.0f - pbr.metallic) * pbr.albedo.xyz * data.direct.color;
direct_diffuse *= remainder;
direct_diffuse = max(0, direct_diffuse);
diffuse += direct_diffuse;
}
// Indirect
#if !defined(FURNACE_TEST_DIRECT) && defined(FORWARD_BASE_PASS)
{
float3 specular_dfg = dfg.xxx * f0_color + dfg.yyy; // filament 5.3.4.6
float3 indirect_specular = data.indirect.specular * specular_dfg;
specular += indirect_specular;
float3 indirect_diffuse = pbr.albedo.xyz * data.indirect.diffuse * (1.0 - pbr.metallic);
diffuse += indirect_diffuse;
}
#endif
return float4(diffuse + specular, 1);
}
#endif // __BRDF_INC
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