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/*
* Copyright 2011-2017 Blender Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef __BSDF_PRINCIPLED_SHEEN_H__
#define __BSDF_PRINCIPLED_SHEEN_H__
/* DISNEY PRINCIPLED SHEEN BRDF
*
* Shading model by Brent Burley (Disney): "Physically Based Shading at Disney" (2012)
*/
CCL_NAMESPACE_BEGIN
typedef ccl_addr_space struct PrincipledSheenBsdf {
SHADER_CLOSURE_BASE;
float avg_value;
} 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, 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);
}
ccl_device int bsdf_principled_sheen_setup(const ShaderData *sd, 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 float3 bsdf_principled_sheen_eval_reflect(const ShaderClosure *sc,
const float3 I,
const float3 omega_in,
float *pdf)
{
const PrincipledSheenBsdf *bsdf = (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 = fmaxf(dot(N, omega_in), 0.0f) * M_1_PI_F;
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(const ShaderClosure *sc,
const float3 I,
const float3 omega_in,
float *pdf)
{
return make_float3(0.0f, 0.0f, 0.0f);
}
ccl_device int bsdf_principled_sheen_sample(const ShaderClosure *sc,
float3 Ng,
float3 I,
float3 dIdx,
float3 dIdy,
float randu,
float randv,
float3 *eval,
float3 *omega_in,
float3 *domega_in_dx,
float3 *domega_in_dy,
float *pdf)
{
const PrincipledSheenBsdf *bsdf = (const PrincipledSheenBsdf *)sc;
float3 N = bsdf->N;
sample_cos_hemisphere(N, randu, randv, omega_in, pdf);
if (dot(Ng, *omega_in) > 0) {
float3 H = normalize(I + *omega_in);
*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 {
*pdf = 0.0f;
}
return LABEL_REFLECT | LABEL_DIFFUSE;
}
CCL_NAMESPACE_END
#endif /* __BSDF_PRINCIPLED_SHEEN_H__ */
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