💿🐜 Antkeeper source code
https://antkeeper.com
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54 lines
1.8 KiB
54 lines
1.8 KiB
/*
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* Copyright (C) 2021 Christopher J. Howard
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*
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* This file is part of Antkeeper source code.
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*
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* Antkeeper source code is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Antkeeper source code is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Antkeeper source code. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "blackbody.hpp"
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#include <algorithm>
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namespace astro
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{
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/// Transforms colors from CIE XYZ to linear RGB
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static constexpr double3x3 xyz_to_rgb =
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{
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3.2404542, -0.9692660, 0.0556434,
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-1.5371385, 1.8760108, -0.2040259,
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-0.4985314, 0.0415560, 1.0572252
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};
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double3 blackbody(double t)
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{
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// Approximate the Planckian locus in CIE 1960 UCS color space (Krystek's algorithm)
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double tt = t * t;
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double u = (0.860117757 + 1.54118254e-4 * t + 1.28641212e-7 * tt) / (1.0 + 8.42420235e-4 * t + 7.08145163e-7 * tt);
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double v = (0.317398726 + 4.22806245e-5 * t + 4.20481691e-8 * tt) / (1.0 - 2.89741816e-5 * t + 1.61456053e-7 * tt);
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// CIE 1960 UCS -> CIE xyY, Y = 1
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double2 xyy = double2{3.0 * u, 2.0 * v} / (2.0 * u - 8.0 * v + 4.0);
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// CIE xyY -> CIE XYZ
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double3 xyz = {xyy.x / xyy.y, 1.0, (1.0 - xyy.x - xyy.y) / xyy.y};
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// CIE XYZ -> linear RGB
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double3 rgb = xyz_to_rgb * xyz;
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// Normalize RGB to preserve chromaticity
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return rgb / std::max<double>(rgb.x, std::max<double>(rgb.y, rgb.z));
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}
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} // namespace astro
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