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/* SPDX-License-Identifier: Apache-2.0
* Copyright 2011-2022 Blender Foundation */
#pragma once
/* DISNEY PRINCIPLED SHEEN BRDF
*
* Shading model by Brent Burley (Disney): "Physically Based Shading at Disney" (2012)
*/
#include "kernel/closure/bsdf_util.h"
CCL_NAMESPACE_BEGIN
typedef struct PrincipledSheenBsdf {
SHADER_CLOSURE_BASE;
float avg_value;
float roughness;
} PrincipledSheenBsdf;
static_assert(sizeof(ShaderClosure) >= sizeof(PrincipledSheenBsdf),
"PrincipledSheenBsdf is too large!");
ccl_device_inline float calculate_avg_principled_sheen_brdf(float3 N, float3 I)
{
/* To compute the average, we set the half-vector to the normal, resulting in
* NdotI = NdotL = NdotV = LdotH */
float NdotI = dot(N, I);
if (NdotI < 0.0f) {
return 0.0f;
}
return schlick_fresnel(NdotI) * NdotI;
}
ccl_device float3
calculate_principled_sheen_brdf(float3 N, float3 V, float3 L, float3 H, ccl_private float *pdf)
{
float NdotL = dot(N, L);
float NdotV = dot(N, V);
if (NdotL < 0 || NdotV < 0) {
*pdf = 0.0f;
return make_float3(0.0f, 0.0f, 0.0f);
}
float LdotH = dot(L, H);
float value = schlick_fresnel(LdotH) * NdotL;
return make_float3(value, value, value);
}
/* Based on
* https://dassaultsystemes-technology.github.io/EnterprisePBRShadingModel/spec-2022x.md.html#components/sheen.
*/
ccl_device_inline float sheen_v2_lambda(float mu, float w)
{
float a = mix(11.9095f, 13.7000f, w);
float b = mix(4.68753f, 2.92754f, w);
float c = mix(0.33467f, 0.28670f, w);
float d = mix(-2.22664f, -0.81757f, w);
float e = mix(-1.76591f, -1.22466f, w);
float exponent;
if (mu < 0.5f) {
exponent = a / (1 + b * powf(mu, c)) + d * mu + e;
}
else {
exponent = 2 * a / (1 + b * exp2(-c)) - a / (1 + b * powf(1 - mu, c)) + d * mu + e;
}
return expf(exponent);
}
ccl_device_inline float3 sheen_v2_eval(float3 N, float3 V, float3 L, float3 H, float r, float *pdf)
{
float cosNH = dot(N, H), cosNV = dot(N, V), cosNL = dot(N, L);
if (cosNH < 0 || cosNV < 0 || cosNL < 0) {
return zero_float3();
}
/* Evaluate microfacet distribution. */
float sinTheta2 = 1 - sqr(cosNH);
float invR = 1 / r;
float D = M_1_2PI_F * (2 + invR) * powf(sinTheta2, 0.5f * invR);
/* Evaluate shadowing-masking terms. */
float w = -1.59612f / (1 + 0.20375f * fast_safe_powf(r, -0.55825f)) + 1.32805f;
float lambdaV = sheen_v2_lambda(cosNV, w);
float lambdaL = sheen_v2_lambda(cosNL, w);
/* Soften shadow terminator. */
lambdaL = fast_safe_powf(lambdaL, 1 + 2 * sqr(sqr(sqr(1 - cosNL))));
/* Combined microfacet BSDF.
* Usual form is F*D*G/(4*cosNL*cosNV), but here we have no Fresnel, we skip dividing by cosNL
* since Cycles convention is returning BSDF*cosNL, and we use the combined shadowing-masking
* term G=1/(1+lambdaV+lambdaL).
*/
float val = D / (4 * cosNV * (1 + lambdaV + lambdaL));
return make_float3(val, val, val);
}
ccl_device_forceinline float sheen_v2_E(KernelGlobals kg, float mu, float rough)
{
return lookup_table_read_2D(kg, mu, 1 - sqrtf(rough), kernel_data.tables.sheen_E_offset, 32, 32);
}
ccl_device int bsdf_principled_sheen_setup(ccl_private const ShaderData *sd,
ccl_private PrincipledSheenBsdf *bsdf)
{
bsdf->type = CLOSURE_BSDF_PRINCIPLED_SHEEN_ID;
bsdf->avg_value = calculate_avg_principled_sheen_brdf(bsdf->N, sd->I);
bsdf->sample_weight *= bsdf->avg_value;
return SD_BSDF | SD_BSDF_HAS_EVAL;
}
ccl_device int bsdf_principled_sheen_v2_setup(KernelGlobals kg,
ccl_private const ShaderData *sd,
ccl_private PrincipledSheenBsdf *bsdf)
{
// TODO: Also expose as separate node. Add enum to Velvet BSDF maybe?
bsdf->type = CLOSURE_BSDF_PRINCIPLED_SHEEN_V2_ID;
bsdf->roughness = clamp(bsdf->roughness, 1e-3f, 1.0f);
bsdf->avg_value = sheen_v2_E(kg, dot(bsdf->N, sd->I), bsdf->roughness);
bsdf->sample_weight *= bsdf->avg_value;
return SD_BSDF | SD_BSDF_HAS_EVAL;
}
ccl_device float3 bsdf_principled_sheen_eval_reflect(ccl_private const ShaderClosure *sc,
const float3 I,
const float3 omega_in,
ccl_private float *pdf)
{
ccl_private const PrincipledSheenBsdf *bsdf = (ccl_private const PrincipledSheenBsdf *)sc;
float3 N = bsdf->N;
float3 V = I; // outgoing
float3 L = omega_in; // incoming
float3 H = normalize(L + V);
if (dot(N, omega_in) > 0.0f) {
*pdf = M_1_2PI_F;
if (bsdf->type == CLOSURE_BSDF_PRINCIPLED_SHEEN_V2_ID) {
return sheen_v2_eval(N, V, L, H, bsdf->roughness, pdf);
}
else {
return calculate_principled_sheen_brdf(N, V, L, H, pdf);
}
}
else {
*pdf = 0.0f;
return make_float3(0.0f, 0.0f, 0.0f);
}
}
ccl_device float3 bsdf_principled_sheen_eval_transmit(ccl_private const ShaderClosure *sc,
const float3 I,
const float3 omega_in,
ccl_private float *pdf)
{
*pdf = 0.0f;
return make_float3(0.0f, 0.0f, 0.0f);
}
ccl_device int bsdf_principled_sheen_sample(ccl_private const ShaderClosure *sc,
float3 Ng,
float3 I,
float3 dIdx,
float3 dIdy,
float randu,
float randv,
ccl_private float3 *eval,
ccl_private float3 *omega_in,
ccl_private float3 *domega_in_dx,
ccl_private float3 *domega_in_dy,
ccl_private float *pdf)
{
ccl_private const PrincipledSheenBsdf *bsdf = (ccl_private const PrincipledSheenBsdf *)sc;
float3 N = bsdf->N;
sample_uniform_hemisphere(N, randu, randv, omega_in, pdf);
if (dot(Ng, *omega_in) > 0) {
float3 H = normalize(I + *omega_in);
if (bsdf->type == CLOSURE_BSDF_PRINCIPLED_SHEEN_V2_ID) {
*eval = sheen_v2_eval(N, I, *omega_in, H, bsdf->roughness, pdf);
}
else {
*eval = calculate_principled_sheen_brdf(N, I, *omega_in, H, pdf);
}
#ifdef __RAY_DIFFERENTIALS__
// TODO: find a better approximation for the diffuse bounce
*domega_in_dx = -((2 * dot(N, dIdx)) * N - dIdx);
*domega_in_dy = -((2 * dot(N, dIdy)) * N - dIdy);
#endif
}
else {
*eval = make_float3(0.0f, 0.0f, 0.0f);
*pdf = 0.0f;
}
return LABEL_REFLECT | LABEL_DIFFUSE;
}
CCL_NAMESPACE_END
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