forked from bartvdbraak/blender
c4d6fd3ec0
This matches behavior of Multiscatter GGX and could become handy later on when/if we decide it would be beneficial to replace on closure with another. Reviewers: lukasstockner97, brecht Reviewed By: brecht Differential Revision: https://developer.blender.org/D2413
236 lines
7.3 KiB
C
236 lines
7.3 KiB
C
/*
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* Copyright 2011-2014 Blender Foundation
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef __BSDF_ASHIKHMIN_SHIRLEY_H__
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#define __BSDF_ASHIKHMIN_SHIRLEY_H__
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/*
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ASHIKHMIN SHIRLEY BSDF
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Implementation of
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Michael Ashikhmin and Peter Shirley: "An Anisotropic Phong BRDF Model" (2000)
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The Fresnel factor is missing to get a separable bsdf (intensity*color), as is
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the case with all other microfacet-based BSDF implementations in Cycles.
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Other than that, the implementation directly follows the paper.
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*/
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CCL_NAMESPACE_BEGIN
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ccl_device int bsdf_ashikhmin_shirley_setup(MicrofacetBsdf *bsdf)
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{
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bsdf->alpha_x = clamp(bsdf->alpha_x, 1e-4f, 1.0f);
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bsdf->alpha_y = bsdf->alpha_x;
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bsdf->type = CLOSURE_BSDF_ASHIKHMIN_SHIRLEY_ID;
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return SD_BSDF|SD_BSDF_HAS_EVAL;
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}
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ccl_device int bsdf_ashikhmin_shirley_aniso_setup(MicrofacetBsdf *bsdf)
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{
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bsdf->alpha_x = clamp(bsdf->alpha_x, 1e-4f, 1.0f);
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bsdf->alpha_y = clamp(bsdf->alpha_y, 1e-4f, 1.0f);
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bsdf->type = CLOSURE_BSDF_ASHIKHMIN_SHIRLEY_ANISO_ID;
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return SD_BSDF|SD_BSDF_HAS_EVAL;
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}
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ccl_device void bsdf_ashikhmin_shirley_blur(ShaderClosure *sc, float roughness)
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{
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MicrofacetBsdf *bsdf = (MicrofacetBsdf*)sc;
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bsdf->alpha_x = fmaxf(roughness, bsdf->alpha_x);
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bsdf->alpha_y = fmaxf(roughness, bsdf->alpha_y);
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}
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ccl_device_inline float bsdf_ashikhmin_shirley_roughness_to_exponent(float roughness)
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{
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return 2.0f / (roughness*roughness) - 2.0f;
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}
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ccl_device_forceinline float3 bsdf_ashikhmin_shirley_eval_reflect(
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const ShaderClosure *sc,
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const float3 I,
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const float3 omega_in,
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float *pdf)
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{
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const MicrofacetBsdf *bsdf = (const MicrofacetBsdf*)sc;
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float3 N = bsdf->N;
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float NdotI = dot(N, I); /* in Cycles/OSL convention I is omega_out */
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float NdotO = dot(N, omega_in); /* and consequently we use for O omaga_in ;) */
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float out = 0.0f;
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if(fmaxf(bsdf->alpha_x, bsdf->alpha_y) <= 1e-4f)
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return make_float3(0.0f, 0.0f, 0.0f);
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if(NdotI > 0.0f && NdotO > 0.0f) {
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NdotI = fmaxf(NdotI, 1e-6f);
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NdotO = fmaxf(NdotO, 1e-6f);
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float3 H = normalize(omega_in + I);
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float HdotI = fmaxf(fabsf(dot(H, I)), 1e-6f);
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float HdotN = fmaxf(dot(H, N), 1e-6f);
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float pump = 1.0f / fmaxf(1e-6f, (HdotI*fmaxf(NdotO, NdotI))); /* pump from original paper (first derivative disc., but cancels the HdotI in the pdf nicely) */
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/*float pump = 1.0f / fmaxf(1e-4f, ((NdotO + NdotI) * (NdotO*NdotI))); */ /* pump from d-brdf paper */
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float n_x = bsdf_ashikhmin_shirley_roughness_to_exponent(bsdf->alpha_x);
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float n_y = bsdf_ashikhmin_shirley_roughness_to_exponent(bsdf->alpha_y);
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if(n_x == n_y) {
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/* isotropic */
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float e = n_x;
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float lobe = powf(HdotN, e);
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float norm = (n_x + 1.0f) / (8.0f * M_PI_F);
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out = NdotO * norm * lobe * pump;
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*pdf = norm * lobe / HdotI; /* this is p_h / 4(H.I) (conversion from 'wh measure' to 'wi measure', eq. 8 in paper) */
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}
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else {
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/* anisotropic */
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float3 X, Y;
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make_orthonormals_tangent(N, bsdf->T, &X, &Y);
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float HdotX = dot(H, X);
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float HdotY = dot(H, Y);
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float lobe;
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if(HdotN < 1.0f) {
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float e = (n_x * HdotX*HdotX + n_y * HdotY*HdotY) / (1.0f - HdotN*HdotN);
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lobe = powf(HdotN, e);
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}
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else {
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lobe = 1.0f;
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}
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float norm = sqrtf((n_x + 1.0f)*(n_y + 1.0f)) / (8.0f * M_PI_F);
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out = NdotO * norm * lobe * pump;
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*pdf = norm * lobe / HdotI;
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}
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}
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return make_float3(out, out, out);
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}
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ccl_device float3 bsdf_ashikhmin_shirley_eval_transmit(const ShaderClosure *sc, const float3 I, const float3 omega_in, float *pdf)
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{
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return make_float3(0.0f, 0.0f, 0.0f);
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}
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ccl_device_inline void bsdf_ashikhmin_shirley_sample_first_quadrant(float n_x, float n_y, float randu, float randv, float *phi, float *cos_theta)
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{
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*phi = atanf(sqrtf((n_x + 1.0f) / (n_y + 1.0f)) * tanf(M_PI_2_F * randu));
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float cos_phi = cosf(*phi);
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float sin_phi = sinf(*phi);
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*cos_theta = powf(randv, 1.0f / (n_x * cos_phi*cos_phi + n_y * sin_phi*sin_phi + 1.0f));
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}
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ccl_device int bsdf_ashikhmin_shirley_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)
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{
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const MicrofacetBsdf *bsdf = (const MicrofacetBsdf*)sc;
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float3 N = bsdf->N;
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int label = LABEL_REFLECT | LABEL_GLOSSY;
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float NdotI = dot(N, I);
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if(NdotI > 0.0f) {
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float n_x = bsdf_ashikhmin_shirley_roughness_to_exponent(bsdf->alpha_x);
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float n_y = bsdf_ashikhmin_shirley_roughness_to_exponent(bsdf->alpha_y);
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/* get x,y basis on the surface for anisotropy */
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float3 X, Y;
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if(n_x == n_y)
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make_orthonormals(N, &X, &Y);
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else
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make_orthonormals_tangent(N, bsdf->T, &X, &Y);
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/* sample spherical coords for h in tangent space */
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float phi;
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float cos_theta;
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if(n_x == n_y) {
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/* isotropic sampling */
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phi = M_2PI_F * randu;
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cos_theta = powf(randv, 1.0f / (n_x + 1.0f));
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}
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else {
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/* anisotropic sampling */
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if(randu < 0.25f) { /* first quadrant */
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float remapped_randu = 4.0f * randu;
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bsdf_ashikhmin_shirley_sample_first_quadrant(n_x, n_y, remapped_randu, randv, &phi, &cos_theta);
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}
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else if(randu < 0.5f) { /* second quadrant */
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float remapped_randu = 4.0f * (.5f - randu);
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bsdf_ashikhmin_shirley_sample_first_quadrant(n_x, n_y, remapped_randu, randv, &phi, &cos_theta);
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phi = M_PI_F - phi;
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}
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else if(randu < 0.75f) { /* third quadrant */
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float remapped_randu = 4.0f * (randu - 0.5f);
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bsdf_ashikhmin_shirley_sample_first_quadrant(n_x, n_y, remapped_randu, randv, &phi, &cos_theta);
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phi = M_PI_F + phi;
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}
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else { /* fourth quadrant */
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float remapped_randu = 4.0f * (1.0f - randu);
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bsdf_ashikhmin_shirley_sample_first_quadrant(n_x, n_y, remapped_randu, randv, &phi, &cos_theta);
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phi = 2.0f * M_PI_F - phi;
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}
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}
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/* get half vector in tangent space */
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float sin_theta = sqrtf(fmaxf(0.0f, 1.0f - cos_theta*cos_theta));
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float cos_phi = cosf(phi);
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float sin_phi = sinf(phi); /* no sqrt(1-cos^2) here b/c it causes artifacts */
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float3 h = make_float3(
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sin_theta * cos_phi,
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sin_theta * sin_phi,
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cos_theta
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);
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/* half vector to world space */
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float3 H = h.x*X + h.y*Y + h.z*N;
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float HdotI = dot(H, I);
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if(HdotI < 0.0f) H = -H;
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/* reflect I on H to get omega_in */
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*omega_in = -I + (2.0f * HdotI) * H;
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if(fmaxf(bsdf->alpha_x, bsdf->alpha_y) <= 1e-4f) {
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/* Some high number for MIS. */
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*pdf = 1e6f;
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*eval = make_float3(1e6f, 1e6f, 1e6f);
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label = LABEL_REFLECT | LABEL_SINGULAR;
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}
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else {
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/* leave the rest to eval_reflect */
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*eval = bsdf_ashikhmin_shirley_eval_reflect(sc, I, *omega_in, pdf);
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}
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#ifdef __RAY_DIFFERENTIALS__
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/* just do the reflection thing for now */
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*domega_in_dx = (2.0f * dot(N, dIdx)) * N - dIdx;
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*domega_in_dy = (2.0f * dot(N, dIdy)) * N - dIdy;
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#endif
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}
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return label;
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}
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CCL_NAMESPACE_END
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#endif /* __BSDF_ASHIKHMIN_SHIRLEY_H__ */
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