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/* SPDX-License-Identifier: Apache-2.0
* Copyright 2011-2022 Blender Foundation */
#pragma once
/* DISNEY PRINCIPLED DIFFUSE BRDF
*
* Shading model by Brent Burley (Disney): "Physically Based Shading at Disney" (2012)
*
* "Extending the Disney BRDF to a BSDF with Integrated Subsurface Scattering" (2015)
* For the separation of retro-reflection, "2.3 Dielectric BRDF with integrated
* subsurface scattering"
*/
#include "kernel/closure/bsdf_util.h"
#include "kernel/sample/mapping.h"
CCL_NAMESPACE_BEGIN
enum PrincipledDiffuseBsdfComponents {
PRINCIPLED_DIFFUSE_FULL = 1,
PRINCIPLED_DIFFUSE_LAMBERT = 2,
PRINCIPLED_DIFFUSE_LAMBERT_EXIT = 4,
PRINCIPLED_DIFFUSE_RETRO_REFLECTION = 8,
};
typedef struct PrincipledDiffuseBsdf {
SHADER_CLOSURE_BASE;
float roughness;
int components;
} PrincipledDiffuseBsdf;
static_assert(sizeof(ShaderClosure) >= sizeof(PrincipledDiffuseBsdf),
"PrincipledDiffuseBsdf is too large!");
ccl_device int bsdf_principled_diffuse_setup(ccl_private PrincipledDiffuseBsdf *bsdf)
{
bsdf->type = CLOSURE_BSDF_PRINCIPLED_DIFFUSE_ID;
bsdf->components = PRINCIPLED_DIFFUSE_FULL;
return SD_BSDF | SD_BSDF_HAS_EVAL;
}
ccl_device Spectrum
bsdf_principled_diffuse_compute_brdf(ccl_private const PrincipledDiffuseBsdf *bsdf,
float3 N,
float3 V,
float3 L,
ccl_private float *pdf)
{
const float NdotL = dot(N, L);
if (NdotL <= 0) {
return zero_spectrum();
}
const float NdotV = dot(N, V);
const float FV = schlick_fresnel(NdotV);
const float FL = schlick_fresnel(NdotL);
float f = 0.0f;
/* Lambertian component. */
if (bsdf->components & (PRINCIPLED_DIFFUSE_FULL | PRINCIPLED_DIFFUSE_LAMBERT)) {
f += (1.0f - 0.5f * FV) * (1.0f - 0.5f * FL);
}
else if (bsdf->components & PRINCIPLED_DIFFUSE_LAMBERT_EXIT) {
f += (1.0f - 0.5f * FL);
}
/* Retro-reflection component. */
if (bsdf->components & (PRINCIPLED_DIFFUSE_FULL | PRINCIPLED_DIFFUSE_RETRO_REFLECTION)) {
/* H = normalize(L + V); // Bisector of an angle between L and V
* LH2 = 2 * dot(L, H)^2 = 2cos(x)^2 = cos(2x) + 1 = dot(L, V) + 1,
* half-angle x between L and V is at most 90 deg. */
const float LH2 = dot(L, V) + 1;
const float RR = bsdf->roughness * LH2;
f += RR * (FL + FV + FL * FV * (RR - 1.0f));
}
float value = M_1_PI_F * NdotL * f;
return make_spectrum(value);
}
/* Compute Fresnel at entry point, to be combined with #PRINCIPLED_DIFFUSE_LAMBERT_EXIT
* at the exit point to get the complete BSDF. */
ccl_device_inline float bsdf_principled_diffuse_compute_entry_fresnel(const float NdotV)
{
const float FV = schlick_fresnel(NdotV);
return (1.0f - 0.5f * FV);
}
/* Ad-hoc weight adjustment to avoid retro-reflection taking away half the
* samples from BSSRDF. */
ccl_device_inline float bsdf_principled_diffuse_retro_reflection_sample_weight(
ccl_private PrincipledDiffuseBsdf *bsdf, const float3 I)
{
return bsdf->roughness * schlick_fresnel(dot(bsdf->N, I));
}
ccl_device int bsdf_principled_diffuse_setup(ccl_private PrincipledDiffuseBsdf *bsdf,
int components)
{
bsdf->type = CLOSURE_BSDF_PRINCIPLED_DIFFUSE_ID;
bsdf->components = components;
return SD_BSDF | SD_BSDF_HAS_EVAL;
}
ccl_device Spectrum bsdf_principled_diffuse_eval_reflect(ccl_private const ShaderClosure *sc,
const float3 I,
const float3 omega_in,
ccl_private float *pdf)
{
ccl_private const PrincipledDiffuseBsdf *bsdf = (ccl_private const PrincipledDiffuseBsdf *)sc;
float3 N = bsdf->N;
float3 V = I; // outgoing
float3 L = omega_in; // incoming
if (dot(N, omega_in) > 0.0f) {
*pdf = fmaxf(dot(N, omega_in), 0.0f) * M_1_PI_F;
return bsdf_principled_diffuse_compute_brdf(bsdf, N, V, L, pdf);
}
else {
*pdf = 0.0f;
return zero_spectrum();
}
}
ccl_device Spectrum bsdf_principled_diffuse_eval_transmit(ccl_private const ShaderClosure *sc,
const float3 I,
const float3 omega_in,
ccl_private float *pdf)
{
*pdf = 0.0f;
return zero_spectrum();
}
ccl_device int bsdf_principled_diffuse_sample(ccl_private const ShaderClosure *sc,
float3 Ng,
float3 I,
float randu,
float randv,
ccl_private Spectrum *eval,
ccl_private float3 *omega_in,
ccl_private float *pdf)
{
ccl_private const PrincipledDiffuseBsdf *bsdf = (ccl_private const PrincipledDiffuseBsdf *)sc;
float3 N = bsdf->N;
sample_cos_hemisphere(N, randu, randv, omega_in, pdf);
if (dot(Ng, *omega_in) > 0) {
*eval = bsdf_principled_diffuse_compute_brdf(bsdf, N, I, *omega_in, pdf);
}
else {
*pdf = 0.0f;
*eval = zero_spectrum();
}
return LABEL_REFLECT | LABEL_DIFFUSE;
}
CCL_NAMESPACE_END
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