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Cycles: Add thin film iridescence to Principled BSDF #118477

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Lukas Stockner merged 18 commits from LukasStockner/blender:iridescence into main 2024-05-02 14:28:57 +02:00
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1 changed files with 16 additions and 13 deletions
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29
intern/cycles/kernel/closure/bsdf_microfacet.h
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@ -421,21 +421,24 @@ ccl_device Spectrum bsdf_microfacet_estimate_albedo(KernelGlobals kg,
if (!is_zero(reflectance) && bsdf->fresnel_type == MicrofacetFresnel::GENERALIZED_SCHLICK) {
ccl_private FresnelGeneralizedSchlick *fresnel = (ccl_private FresnelGeneralizedSchlick *)
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Weizhen Huang commented 2024-04-16 15:12:29 +02:00
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What is this TODO?

What is this TODO?
Lukas Stockner commented 2024-04-22 01:50:32 +02:00
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The code here wasn't accounting for the thin film yet, this is fixed now.

The code here wasn't accounting for the thin film yet, this is fixed now.
bsdf->fresnel;
/* TODO: Iridescence */
float rough = sqrtf(sqrtf(bsdf->alpha_x * bsdf->alpha_y));
float s;
if (fresnel->exponent < 0.0f) {
float z = sqrtf(fabsf((bsdf->ior - 1.0f) / (bsdf->ior + 1.0f)));
s = lookup_table_read_3D(
kg, rough, cos_NI, z, kernel_data.tables.ggx_gen_schlick_ior_s, 16, 16, 16);
/* Precomputing LUTs for thin-film iridescence isn't viable, so fall back to the specular
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Weizhen Huang commented 2024-04-22 12:17:16 +02:00
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For cognitive ease I would prefer to add an empty if (fresnel->thin_film.thickness > 0.1f) branch and put the comment there, the following block is then put in the else branch

For cognitive ease I would prefer to add an empty `if (fresnel->thin_film.thickness > 0.1f)` branch and put the comment there, the following block is then put in the `else` branch
👍 1
* reflection approximation from the microfacet_fresnel call above in that case. */
if (fresnel->thin_film.thickness <= 0.1f) {
float rough = sqrtf(sqrtf(bsdf->alpha_x * bsdf->alpha_y));
float s;
if (fresnel->exponent < 0.0f) {
float z = sqrtf(fabsf((bsdf->ior - 1.0f) / (bsdf->ior + 1.0f)));
s = lookup_table_read_3D(
kg, rough, cos_NI, z, kernel_data.tables.ggx_gen_schlick_ior_s, 16, 16, 16);
}
else {
float z = 1.0f / (0.2f * fresnel->exponent + 1.0f);
s = lookup_table_read_3D(
kg, rough, cos_NI, z, kernel_data.tables.ggx_gen_schlick_s, 16, 16, 16);
}
reflectance = mix(fresnel->f0, fresnel->f90, s) * fresnel->reflection_tint;
}
else {
float z = 1.0f / (0.2f * fresnel->exponent + 1.0f);
s = lookup_table_read_3D(
kg, rough, cos_NI, z, kernel_data.tables.ggx_gen_schlick_s, 16, 16, 16);
}
reflectance = mix(fresnel->f0, fresnel->f90, s) * fresnel->reflection_tint;
}
else if (bsdf->fresnel_type == MicrofacetFresnel::F82_TINT) {
ccl_private FresnelF82Tint *fresnel = (ccl_private FresnelF82Tint *)bsdf->fresnel;