hsl.cpp

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// SPDX-License-Identifier: GPL-2.0-or-later
 * Authors: see git history
 *
 * Copyright (C) 2023 Authors
 * Released under GNU GPL v2+, read the file 'COPYING' for more information.
 */
 
#include "hsl.h"
 
#include <cmath>
 
#include "colors/color.h"
#include "colors/printer.h"
 
namespace Inkscape::Colors::Space {
 
static float hue_2_rgb(float v1, float v2, float h)
{
    if (h < 0)
        h += 6.0;
    if (h > 6)
        h -= 6.0;
    if (h < 1)
        return v1 + (v2 - v1) * h;
    if (h < 3)
        return v2;
    if (h < 4)
        return v1 + (v2 - v1) * (4 - h);
    return v1;
}
 
void HSL::spaceToProfile(std::vector<double> &output) const
{
    double h = output[0];
    double s = output[1];
    double l = output[2];
 
    if (s == 0) { // Gray
        output[0] = l;
        output[1] = l;
        output[2] = l;
    } else {
        double v2;
        if (l < 0.5) {
            v2 = l * (1 + s);
        } else {
            v2 = l + s - l * s;
        }
        double v1 = 2 * l - v2;
 
        output[0] = hue_2_rgb(v1, v2, h * 6 + 2.0);
        output[1] = hue_2_rgb(v1, v2, h * 6);
        output[2] = hue_2_rgb(v1, v2, h * 6 - 2.0);
    }
}
 
void HSL::profileToSpace(std::vector<double> &output) const
{
    double r = output[0];
    double g = output[1];
    double b = output[2];
 
    double max = std::max(std::max(r, g), b);
    double min = std::min(std::min(r, g), b);
    double delta = max - min;
 
    double h = 0;
    double s = 0;
    double l = (max + min) / 2.0;
 
    if (delta != 0) {
        if (l <= 0.5)
            s = delta / (max + min);
        else
            s = delta / (2 - max - min);
 
        if (r == max)
            h = (g - b) / delta;
        else if (g == max)
            h = 2.0 + (b - r) / delta;
        else if (b == max)
            h = 4.0 + (r - g) / delta;
 
        h = h / 6.0;
 
        if (h < 0)
            h += 1;
        if (h > 1)
            h -= 1;
    }
    output[0] = h;
    output[1] = s;
    output[2] = l;
}
 
std::string HSL::toString(std::vector<double> const &values, bool opacity) const
{
    auto oo = CssLegacyPrinter(3, "hsl", opacity && values.size() == 4);
    // First entry is Hue, which is in degrees
    return oo << (int)(values[0] * 360) << values[1] << values[2] << values.back();
}
 
}; // namespace Inkscape::Colors::Space