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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
#include "kernel/sample/mapping.h"
CCL_NAMESPACE_BEGIN
typedef struct VelvetBsdf {
SHADER_CLOSURE_BASE;
float sigma;
float invsigma2;
} VelvetBsdf;
static_assert(sizeof(ShaderClosure) >= sizeof(VelvetBsdf), "VelvetBsdf is too large!");
ccl_device int bsdf_ashikhmin_velvet_setup(ccl_private VelvetBsdf *bsdf)
{
float sigma = fmaxf(bsdf->sigma, 0.01f);
bsdf->invsigma2 = 1.0f / (sigma * sigma);
bsdf->type = CLOSURE_BSDF_ASHIKHMIN_VELVET_ID;
return SD_BSDF | SD_BSDF_HAS_EVAL;
}
ccl_device float3 bsdf_ashikhmin_velvet_eval_reflect(ccl_private const ShaderClosure *sc,
const float3 I,
const float3 omega_in,
ccl_private float *pdf)
{
ccl_private const VelvetBsdf *bsdf = (ccl_private const VelvetBsdf *)sc;
float m_invsigma2 = bsdf->invsigma2;
float3 N = bsdf->N;
float cosNO = dot(N, I);
float cosNI = dot(N, omega_in);
if (cosNO > 0 && cosNI > 0) {
float3 H = normalize(omega_in + I);
float cosNH = dot(N, H);
float cosHO = fabsf(dot(I, H));
if (!(fabsf(cosNH) < 1.0f - 1e-5f && cosHO > 1e-5f)) {
*pdf = 0.0f;
return make_float3(0.0f, 0.0f, 0.0f);
}
float cosNHdivHO = cosNH / cosHO;
cosNHdivHO = fmaxf(cosNHdivHO, 1e-5f);
float fac1 = 2 * fabsf(cosNHdivHO * cosNO);
float fac2 = 2 * fabsf(cosNHdivHO * cosNI);
float sinNH2 = 1 - cosNH * cosNH;
float sinNH4 = sinNH2 * sinNH2;
float cotangent2 = (cosNH * cosNH) / sinNH2;
float D = expf(-cotangent2 * m_invsigma2) * m_invsigma2 * M_1_PI_F / sinNH4;
float G = fminf(1.0f, fminf(fac1, fac2)); // TODO: derive G from D analytically
float out = 0.25f * (D * G) / cosNO;
*pdf = 0.5f * M_1_PI_F;
return make_float3(out, out, out);
}
*pdf = 0.0f;
return make_float3(0.0f, 0.0f, 0.0f);
}
ccl_device float3 bsdf_ashikhmin_velvet_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_ashikhmin_velvet_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 VelvetBsdf *bsdf = (ccl_private const VelvetBsdf *)sc;
float m_invsigma2 = bsdf->invsigma2;
float3 N = bsdf->N;
// we are viewing the surface from above - send a ray out with uniform
// distribution over the hemisphere
sample_uniform_hemisphere(N, randu, randv, omega_in, pdf);
if (dot(Ng, *omega_in) > 0) {
float3 H = normalize(*omega_in + I);
float cosNI = dot(N, *omega_in);
float cosNO = dot(N, I);
float cosNH = dot(N, H);
float cosHO = fabsf(dot(I, H));
if (fabsf(cosNO) > 1e-5f && fabsf(cosNH) < 1.0f - 1e-5f && cosHO > 1e-5f) {
float cosNHdivHO = cosNH / cosHO;
cosNHdivHO = fmaxf(cosNHdivHO, 1e-5f);
float fac1 = 2 * fabsf(cosNHdivHO * cosNO);
float fac2 = 2 * fabsf(cosNHdivHO * cosNI);
float sinNH2 = 1 - cosNH * cosNH;
float sinNH4 = sinNH2 * sinNH2;
float cotangent2 = (cosNH * cosNH) / sinNH2;
float D = expf(-cotangent2 * m_invsigma2) * m_invsigma2 * M_1_PI_F / sinNH4;
float G = fminf(1.0f, fminf(fac1, fac2)); // TODO: derive G from D analytically
float power = 0.25f * (D * G) / cosNO;
*eval = make_float3(power, power, power);
#ifdef __RAY_DIFFERENTIALS__
// TODO: find a better approximation for the retroreflective bounce
*domega_in_dx = (2 * dot(N, dIdx)) * N - dIdx;
*domega_in_dy = (2 * dot(N, dIdy)) * N - dIdy;
#endif
}
else {
*pdf = 0.0f;
*eval = make_float3(0.0f, 0.0f, 0.0f);
}
}
else {
*pdf = 0.0f;
*eval = make_float3(0.0f, 0.0f, 0.0f);
}
return LABEL_REFLECT | LABEL_DIFFUSE;
}
CCL_NAMESPACE_END
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