59a1148ac0
Fixes an issue where the sheen would render incorrectly when the normal of the surface is parallel to the incoming direction. Co-authored-by: Lukas Stockner <lukas.stockner@freenet.de> Pull Request: https://projects.blender.org/blender/blender/pulls/115286
113 lines
3.6 KiB
C
113 lines
3.6 KiB
C
/* SPDX-FileCopyrightText: Copyright 2011-2022 Blender Foundation
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*
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* SPDX-License-Identifier: Apache-2.0 */
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#pragma once
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/* Shading model by Tizian Zeltner, Brent Burley, Matt Jen-Yuan Chiang:
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* "Practical Multiple-Scattering Sheen Using Linearly Transformed Cosines" (2022)
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* https://tizianzeltner.com/projects/Zeltner2022Practical/
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*/
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#include "kernel/closure/bsdf_util.h"
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CCL_NAMESPACE_BEGIN
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typedef struct SheenBsdf {
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SHADER_CLOSURE_BASE;
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float roughness;
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float transformA, transformB;
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float3 T, B;
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} SheenBsdf;
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static_assert(sizeof(ShaderClosure) >= sizeof(SheenBsdf), "SheenBsdf is too large!");
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ccl_device int bsdf_sheen_setup(KernelGlobals kg,
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ccl_private const ShaderData *sd,
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ccl_private SheenBsdf *bsdf)
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{
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bsdf->type = CLOSURE_BSDF_SHEEN_ID;
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bsdf->roughness = clamp(bsdf->roughness, 1e-3f, 1.0f);
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make_orthonormals_safe_tangent(bsdf->N, sd->wi, &bsdf->T, &bsdf->B);
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float cosNI = dot(bsdf->N, sd->wi);
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int offset = kernel_data.tables.sheen_ltc;
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bsdf->transformA = lookup_table_read_2D(kg, cosNI, bsdf->roughness, offset, 32, 32);
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bsdf->transformB = lookup_table_read_2D(kg, cosNI, bsdf->roughness, offset + 32 * 32, 32, 32);
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float albedo = lookup_table_read_2D(kg, cosNI, bsdf->roughness, offset + 2 * 32 * 32, 32, 32);
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/* If the given roughness and angle result in an invalid LTC, skip the closure. */
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if (fabsf(bsdf->transformA) < 1e-5f || albedo < 1e-5f) {
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bsdf->type = CLOSURE_NONE_ID;
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bsdf->sample_weight = 0.0f;
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return 0;
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}
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bsdf->weight *= albedo;
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bsdf->sample_weight *= albedo;
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return SD_BSDF | SD_BSDF_HAS_EVAL;
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}
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ccl_device Spectrum bsdf_sheen_eval(ccl_private const ShaderClosure *sc,
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const float3 wi,
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const float3 wo,
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ccl_private float *pdf)
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{
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ccl_private const SheenBsdf *bsdf = (ccl_private const SheenBsdf *)sc;
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const float3 N = bsdf->N, T = bsdf->T, B = bsdf->B;
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float a = bsdf->transformA, b = bsdf->transformB;
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if (dot(N, wo) <= 0.0f) {
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*pdf = 0.0f;
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return zero_spectrum();
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}
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float3 localO = make_float3(dot(T, wo), dot(B, wo), dot(N, wo));
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if (localO.z <= 0.0f) {
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*pdf = 0.0f;
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return zero_spectrum();
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}
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float lenSqr = sqr(a * localO.x + b * localO.z) + sqr(a * localO.y) + sqr(localO.z);
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float val = M_1_PI_F * localO.z * sqr(a / lenSqr);
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*pdf = val;
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return make_spectrum(val);
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}
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ccl_device int bsdf_sheen_sample(ccl_private const ShaderClosure *sc,
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float3 Ng,
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float3 wi,
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float2 rand,
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ccl_private Spectrum *eval,
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ccl_private float3 *wo,
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ccl_private float *pdf)
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{
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ccl_private const SheenBsdf *bsdf = (ccl_private const SheenBsdf *)sc;
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const float3 N = bsdf->N, T = bsdf->T, B = bsdf->B;
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float a = bsdf->transformA, b = bsdf->transformB;
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float2 disk = sample_uniform_disk(rand);
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float diskZ = safe_sqrtf(1.0f - dot(disk, disk));
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float3 localO = normalize(make_float3((disk.x - diskZ * b), disk.y, diskZ * a));
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*wo = localO.x * T + localO.y * B + localO.z * N;
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if (dot(Ng, *wo) <= 0) {
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*eval = zero_spectrum();
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*pdf = 0.0f;
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return LABEL_REFLECT | LABEL_DIFFUSE;
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}
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float lenSqr = sqr(a * localO.x + b * localO.z) + sqr(a * localO.y) + sqr(localO.z);
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float val = M_1_PI_F * localO.z * sqr(a / lenSqr);
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*pdf = val;
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*eval = make_spectrum(val);
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return LABEL_REFLECT | LABEL_DIFFUSE;
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}
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CCL_NAMESPACE_END
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