/* spek-palette.c
 *
 * Copyright (C) 2010-2012  Alexander Kojevnikov <alexander@kojevnikov.com>
 *
 * Spek is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Spek is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Spek.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "spek-palette.h"

// Modified version of Dan Bruton's algorithm:
// http://www.physics.sfasu.edu/astro/color/spectra.html
uint32_t spek_palette_spectrum(double level)
{
    level *= 0.6625;
    double r = 0.0, g = 0.0, b = 0.0;
    if (level >= 0 && level < 0.15) {
        r = (0.15 - level) / (0.15 + 0.075);
        g = 0.0;
        b = 1.0;
    } else if (level >= 0.15 && level < 0.275) {
        r = 0.0;
        g = (level - 0.15) / (0.275 - 0.15);
        b = 1.0;
    } else if (level >= 0.275 && level < 0.325) {
        r = 0.0;
        g = 1.0;
        b = (0.325 - level) / (0.325 - 0.275);
    } else if (level >= 0.325 && level < 0.5) {
        r = (level - 0.325) / (0.5 - 0.325);
        g = 1.0;
        b = 0.0;
    } else if (level >= 0.5 && level < 0.6625) {
        r = 1.0;
        g = (0.6625 - level) / (0.6625 - 0.5f);
        b = 0.0;
    }

    // Intensity correction.
    double cf = 1.0;
    if (level >= 0.0 && level < 0.1) {
        cf = level / 0.1;
    }
    cf *= 255.0;

    // Pack RGB values into a 32-bit uint.
    uint32_t rr = (uint32_t) (r * cf + 0.5);
    uint32_t gg = (uint32_t) (g * cf + 0.5);
    uint32_t bb = (uint32_t) (b * cf + 0.5);
    return (rr << 16) + (gg << 8) + bb;
}