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/* SPDX-License-Identifier: BSD-3-Clause
*
* Adapted from Open Shading Language
* Copyright (c) 2009-2010 Sony Pictures Imageworks Inc., et al.
* All Rights Reserved.
*
* Modifications Copyright 2011-2022 Blender Foundation. */
#pragma once
CCL_NAMESPACE_BEGIN
typedef struct HairBsdf {
SHADER_CLOSURE_BASE;
float3 T;
float roughness1;
float roughness2;
float offset;
} HairBsdf;
static_assert(sizeof(ShaderClosure) >= sizeof(HairBsdf), "HairBsdf is too large!");
ccl_device int bsdf_hair_reflection_setup(ccl_private HairBsdf *bsdf)
{
bsdf->type = CLOSURE_BSDF_HAIR_REFLECTION_ID;
bsdf->roughness1 = clamp(bsdf->roughness1, 0.001f, 1.0f);
bsdf->roughness2 = clamp(bsdf->roughness2, 0.001f, 1.0f);
return SD_BSDF | SD_BSDF_HAS_EVAL;
}
ccl_device int bsdf_hair_transmission_setup(ccl_private HairBsdf *bsdf)
{
bsdf->type = CLOSURE_BSDF_HAIR_TRANSMISSION_ID;
bsdf->roughness1 = clamp(bsdf->roughness1, 0.001f, 1.0f);
bsdf->roughness2 = clamp(bsdf->roughness2, 0.001f, 1.0f);
return SD_BSDF | SD_BSDF_HAS_EVAL;
}
ccl_device Spectrum bsdf_hair_reflection_eval_reflect(ccl_private const ShaderClosure *sc,
const float3 I,
const float3 omega_in,
ccl_private float *pdf)
{
ccl_private const HairBsdf *bsdf = (ccl_private const HairBsdf *)sc;
float offset = bsdf->offset;
float3 Tg = bsdf->T;
float roughness1 = bsdf->roughness1;
float roughness2 = bsdf->roughness2;
float Iz = dot(Tg, I);
float3 locy = normalize(I - Tg * Iz);
float theta_r = M_PI_2_F - fast_acosf(Iz);
float omega_in_z = dot(Tg, omega_in);
float3 omega_in_y = normalize(omega_in - Tg * omega_in_z);
float theta_i = M_PI_2_F - fast_acosf(omega_in_z);
float cosphi_i = dot(omega_in_y, locy);
if (M_PI_2_F - fabsf(theta_i) < 0.001f || cosphi_i < 0.0f) {
*pdf = 0.0f;
return zero_spectrum();
}
float roughness1_inv = 1.0f / roughness1;
float roughness2_inv = 1.0f / roughness2;
float phi_i = fast_acosf(cosphi_i) * roughness2_inv;
phi_i = fabsf(phi_i) < M_PI_F ? phi_i : M_PI_F;
float costheta_i = fast_cosf(theta_i);
float a_R = fast_atan2f(((M_PI_2_F + theta_r) * 0.5f - offset) * roughness1_inv, 1.0f);
float b_R = fast_atan2f(((-M_PI_2_F + theta_r) * 0.5f - offset) * roughness1_inv, 1.0f);
float theta_h = (theta_i + theta_r) * 0.5f;
float t = theta_h - offset;
float phi_pdf = fast_cosf(phi_i * 0.5f) * 0.25f * roughness2_inv;
float theta_pdf = roughness1 /
(2 * (t * t + roughness1 * roughness1) * (a_R - b_R) * costheta_i);
*pdf = phi_pdf * theta_pdf;
return make_spectrum(*pdf);
}
ccl_device Spectrum bsdf_hair_transmission_eval_reflect(ccl_private const ShaderClosure *sc,
const float3 I,
const float3 omega_in,
ccl_private float *pdf)
{
*pdf = 0.0f;
return zero_spectrum();
}
ccl_device Spectrum bsdf_hair_reflection_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 Spectrum bsdf_hair_transmission_eval_transmit(ccl_private const ShaderClosure *sc,
const float3 I,
const float3 omega_in,
ccl_private float *pdf)
{
ccl_private const HairBsdf *bsdf = (ccl_private const HairBsdf *)sc;
float offset = bsdf->offset;
float3 Tg = bsdf->T;
float roughness1 = bsdf->roughness1;
float roughness2 = bsdf->roughness2;
float Iz = dot(Tg, I);
float3 locy = normalize(I - Tg * Iz);
float theta_r = M_PI_2_F - fast_acosf(Iz);
float omega_in_z = dot(Tg, omega_in);
float3 omega_in_y = normalize(omega_in - Tg * omega_in_z);
float theta_i = M_PI_2_F - fast_acosf(omega_in_z);
float phi_i = fast_acosf(dot(omega_in_y, locy));
if (M_PI_2_F - fabsf(theta_i) < 0.001f) {
*pdf = 0.0f;
return zero_spectrum();
}
float costheta_i = fast_cosf(theta_i);
float roughness1_inv = 1.0f / roughness1;
float a_TT = fast_atan2f(((M_PI_2_F + theta_r) / 2 - offset) * roughness1_inv, 1.0f);
float b_TT = fast_atan2f(((-M_PI_2_F + theta_r) / 2 - offset) * roughness1_inv, 1.0f);
float c_TT = 2 * fast_atan2f(M_PI_2_F / roughness2, 1.0f);
float theta_h = (theta_i + theta_r) / 2;
float t = theta_h - offset;
float phi = fabsf(phi_i);
float p = M_PI_F - phi;
float theta_pdf = roughness1 /
(2 * (t * t + roughness1 * roughness1) * (a_TT - b_TT) * costheta_i);
float phi_pdf = roughness2 / (c_TT * (p * p + roughness2 * roughness2));
*pdf = phi_pdf * theta_pdf;
return make_spectrum(*pdf);
}
ccl_device int bsdf_hair_reflection_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 HairBsdf *bsdf = (ccl_private const HairBsdf *)sc;
float offset = bsdf->offset;
float3 Tg = bsdf->T;
float roughness1 = bsdf->roughness1;
float roughness2 = bsdf->roughness2;
float Iz = dot(Tg, I);
float3 locy = normalize(I - Tg * Iz);
float3 locx = cross(locy, Tg);
float theta_r = M_PI_2_F - fast_acosf(Iz);
float roughness1_inv = 1.0f / roughness1;
float a_R = fast_atan2f(((M_PI_2_F + theta_r) * 0.5f - offset) * roughness1_inv, 1.0f);
float b_R = fast_atan2f(((-M_PI_2_F + theta_r) * 0.5f - offset) * roughness1_inv, 1.0f);
float t = roughness1 * tanf(randu * (a_R - b_R) + b_R);
float theta_h = t + offset;
float theta_i = 2 * theta_h - theta_r;
float costheta_i, sintheta_i;
fast_sincosf(theta_i, &sintheta_i, &costheta_i);
float phi = 2 * safe_asinf(1 - 2 * randv) * roughness2;
float phi_pdf = fast_cosf(phi * 0.5f) * 0.25f / roughness2;
float theta_pdf = roughness1 /
(2 * (t * t + roughness1 * roughness1) * (a_R - b_R) * costheta_i);
float sinphi, cosphi;
fast_sincosf(phi, &sinphi, &cosphi);
*omega_in = (cosphi * costheta_i) * locy - (sinphi * costheta_i) * locx + (sintheta_i)*Tg;
*pdf = fabsf(phi_pdf * theta_pdf);
if (M_PI_2_F - fabsf(theta_i) < 0.001f)
*pdf = 0.0f;
*eval = make_spectrum(*pdf);
return LABEL_REFLECT | LABEL_GLOSSY;
}
ccl_device int bsdf_hair_transmission_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 HairBsdf *bsdf = (ccl_private const HairBsdf *)sc;
float offset = bsdf->offset;
float3 Tg = bsdf->T;
float roughness1 = bsdf->roughness1;
float roughness2 = bsdf->roughness2;
float Iz = dot(Tg, I);
float3 locy = normalize(I - Tg * Iz);
float3 locx = cross(locy, Tg);
float theta_r = M_PI_2_F - fast_acosf(Iz);
float roughness1_inv = 1.0f / roughness1;
float a_TT = fast_atan2f(((M_PI_2_F + theta_r) / 2 - offset) * roughness1_inv, 1.0f);
float b_TT = fast_atan2f(((-M_PI_2_F + theta_r) / 2 - offset) * roughness1_inv, 1.0f);
float c_TT = 2 * fast_atan2f(M_PI_2_F / roughness2, 1.0f);
float t = roughness1 * tanf(randu * (a_TT - b_TT) + b_TT);
float theta_h = t + offset;
float theta_i = 2 * theta_h - theta_r;
float costheta_i, sintheta_i;
fast_sincosf(theta_i, &sintheta_i, &costheta_i);
float p = roughness2 * tanf(c_TT * (randv - 0.5f));
float phi = p + M_PI_F;
float theta_pdf = roughness1 /
(2 * (t * t + roughness1 * roughness1) * (a_TT - b_TT) * costheta_i);
float phi_pdf = roughness2 / (c_TT * (p * p + roughness2 * roughness2));
float sinphi, cosphi;
fast_sincosf(phi, &sinphi, &cosphi);
*omega_in = (cosphi * costheta_i) * locy - (sinphi * costheta_i) * locx + (sintheta_i)*Tg;
*pdf = fabsf(phi_pdf * theta_pdf);
if (M_PI_2_F - fabsf(theta_i) < 0.001f) {
*pdf = 0.0f;
}
*eval = make_spectrum(*pdf);
/* TODO(sergey): Should always be negative, but seems some precision issue
* is involved here.
*/
kernel_assert(dot(locy, *omega_in) < 1e-4f);
return LABEL_TRANSMIT | LABEL_GLOSSY;
}
CCL_NAMESPACE_END
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