c99b7e66b2
Previous implemenation of 5 < d < 50 was taken from the main paper, fitting for smaller sizes are found in the supplemental. They are less forward-scattering. Pull Request: https://projects.blender.org/blender/blender/pulls/130234
83 lines
2.6 KiB
Plaintext
83 lines
2.6 KiB
Plaintext
/* SPDX-FileCopyrightText: 2011-2022 Blender Foundation
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*
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* SPDX-License-Identifier: Apache-2.0 */
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#include "stdcycles.h"
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struct MieParameters {
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float g_HG;
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float g_D;
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float alpha;
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float mixture;
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};
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MieParameters phase_mie_fitted_parameters(float Diameter)
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{
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float d = max(Diameter, 0.0);
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if (d <= 0.1) {
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/* Eq (11 - 14). */
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return {13.8 * d * d, 1.1456 * d * sin(9.29044 * d), 250.0, 0.252977 - 312.983 * pow(d, 4.3)};
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}
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if (d < 1.5) {
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/* Eq (15 - 18). */
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float log_d = log(d);
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float a = (log_d - 0.238604) * (log_d + 1.00667);
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float b = 0.507522 - 0.15677 * log_d;
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float c = 1.19692 * cos(a / b) + 1.37932 * log_d + 0.0625835;
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return {0.862 - 0.143 * log_d * log_d,
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0.379685 * cos(c) + 0.344213,
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250.0,
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0.146209 * cos(3.38707 * log_d + 2.11193) + 0.316072 + 0.0778917 * log_d};
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}
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if (d < 5.0) {
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/* Eq (19 - 22). */
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float log_d = log(d);
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float temp = cos(5.68947 * (log(log_d) - 0.0292149));
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return {0.0604931 * log(log_d) + 0.940256,
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0.500411 - (0.081287 / (-2.0 * log_d + tan(log_d) + 1.27551)),
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7.30354 * log_d + 6.31675,
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0.026914 * (log_d - temp) + 0.3764};
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}
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/* Eq (7 - 10). */
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return {exp(-0.0990567 / (d - 1.67154)),
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exp(-2.20679 / (d + 3.91029) - 0.428934),
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exp(3.62489 - 8.29288 / (d + 5.52825)),
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exp(-0.599085 / (d - 0.641583) - 0.665888)};
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}
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shader node_scatter_volume(string phase = "Henyey-Greenstein",
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color Color = color(0.8, 0.8, 0.8),
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float Density = 1.0,
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float Anisotropy = 0.0,
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float IOR = 1.33,
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float Backscatter = 0.1,
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float Alpha = 0.5,
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float Diameter = 20.0,
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output closure color Volume = 0)
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{
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closure color scatter = 0;
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if (phase == "Fournier-Forand") {
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scatter = fournier_forand(Backscatter, IOR);
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}
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else if (phase == "Draine") {
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scatter = draine(Anisotropy, Alpha);
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}
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else if (phase == "Rayleigh") {
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scatter = rayleigh();
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}
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else if (phase == "Mie") {
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/* Approximation of Mie phase function for water droplets using a mix of Draine and H-G.
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* See `kernel/svm/closure.h` for details. */
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MieParameters param = phase_mie_fitted_parameters(Diameter);
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scatter = mix(henyey_greenstein(param.g_HG), draine(param.g_D, param.alpha), param.mixture);
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}
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else {
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scatter = henyey_greenstein(Anisotropy);
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}
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Volume = (Color * max(Density, 0.0)) * scatter;
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}
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