0315eae536
Previously, Cycles only supported the Henyey-Greenstein phase function for volume scattering. While HG is flexible and works for a wide range of effects, sometimes a more physically accurate phase function may be needed for realism. Therefore, this adds three new phase functions to the code: Rayleigh: For particles with a size below the wavelength of light, mostly athmospheric scattering. Fournier-Forand: For realistic underwater scattering. Draine: Fairly specific on its own (mostly for interstellar dust), but useful for the next entry. Mie: Approximates Mie scattering in water droplets using a mix of Draine and HG phase functions. These phase functions can be combined using Mix nodes as usual. Co-authored-by: Lukas Stockner <lukas@lukasstockner.de> Pull Request: https://projects.blender.org/blender/blender/pulls/123532
61 lines
1.9 KiB
C
61 lines
1.9 KiB
C
/* SPDX-FileCopyrightText: 2011-2024 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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#include "kernel/closure/volume_util.h"
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CCL_NAMESPACE_BEGIN
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/* DRAINE CLOSURE */
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typedef struct DraineVolume {
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SHADER_CLOSURE_VOLUME_BASE;
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float g;
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float alpha;
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} DraineVolume;
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static_assert(sizeof(ShaderVolumeClosure) >= sizeof(DraineVolume), "DraineVolume is too large!");
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ccl_device int volume_draine_setup(ccl_private DraineVolume *volume)
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{
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volume->type = CLOSURE_VOLUME_DRAINE_ID;
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/* clamp anisotropy */
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volume->g = signf(volume->g) * min(fabsf(volume->g), 1.0f - 1e-3f);
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return SD_SCATTER;
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}
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ccl_device Spectrum volume_draine_eval(ccl_private const ShaderData *sd,
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ccl_private const ShaderVolumeClosure *svc,
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float3 wo,
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ccl_private float *pdf)
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{
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ccl_private const DraineVolume *volume = (ccl_private const DraineVolume *)svc;
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/* note that wi points towards the viewer */
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float cos_theta = dot(-sd->wi, wo);
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*pdf = phase_draine(cos_theta, volume->g, volume->alpha);
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return make_spectrum(*pdf);
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}
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ccl_device int volume_draine_sample(ccl_private const ShaderData *sd,
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ccl_private const ShaderVolumeClosure *svc,
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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 DraineVolume *volume = (ccl_private const DraineVolume *)svc;
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/* note that wi points towards the viewer and so is used negated */
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*wo = phase_draine_sample(-sd->wi, volume->g, volume->alpha, rand, pdf);
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*eval = make_spectrum(*pdf); /* perfect importance sampling */
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return LABEL_VOLUME_SCATTER;
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}
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CCL_NAMESPACE_END
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