ShrlAlgoToolkit/WPFluent/Extensions/HsbExtensions.cs

using System;
using System.Linq;

using WPFluent.Controls;


namespace WPFluent.Extensions
{
    public static class HsbExtensions
    {
        private static bool IsCloseTo(this double value, double target, double tolerance = double.Epsilon) => Math.Abs(
                value - target) <
            tolerance;

        /// <summary>
        /// 将 HSB（色相、饱和度、亮度）颜色空间转换为 Color 对象。
        /// </summary>
        /// <param name="hsb"></param>
        /// <returns></returns>
        /// <exception cref="InvalidOperationException"></exception>
        public static Color ToColor(this Controls.Hsb hsb)
        {
            //0~1
            var hue = hsb.Hue;
            var saturation = hsb.Saturation;
            var brightness = hsb.Brightness;
            var opacity = hsb.Opacity;
            brightness *= 255;
            //饱和度为0，直接返回亮度值
            if (saturation.IsCloseTo(0))
                return Color.FromArgb((byte)brightness, (byte)brightness, (byte)brightness, (byte)brightness);
            opacity *= 255;
            //处理色相超出范围
            if (hue.IsCloseTo(360))
                hue = 0;
            while (hue > 360)
                hue -= 360;
            while (hue < 0)
                hue += 360;

            //通过色相返回颜色
            hue /= 60;
            //以60作为一个区间，通过switch判断
            var i = (int)Math.Floor(hue);
            //计算出色相值在当前区间内的偏移量
            var f = hue - i;
            //计算出低饱和度情况下的亮度值
            var p = brightness * (1 - saturation);
            //计算出中间饱和度情况下的亮度值
            var q = brightness * (1 - saturation * f);
            //计算出高饱和度情况下的亮度值
            var t = brightness * (1 - saturation * (1 - f));

            return i switch
            {
                //[0~60)红色区间
                0 => Color.FromArgb((byte)opacity, (byte)brightness, (byte)t, (byte)p),
                //[60~120)黄色区间
                1 => Color.FromArgb((byte)opacity, (byte)q, (byte)brightness, (byte)p),
                //[120~180)绿色区间
                2 => Color.FromArgb((byte)opacity, (byte)p, (byte)brightness, (byte)t),
                //[180~240)青色区间
                3 => Color.FromArgb((byte)opacity, (byte)p, (byte)q, (byte)brightness),
                //[240~300)蓝色区间
                4 => Color.FromArgb((byte)opacity, (byte)t, (byte)p, (byte)brightness),
                //[300~360)洋红色区间
                5 => Color.FromArgb((byte)opacity, (byte)brightness, (byte)p, (byte)q),
                _ => throw new InvalidOperationException("不可用的HSB值"),
            };
        }

        /// <summary>
        /// 将 Color 对象转换为 HSB（色相、饱和度、亮度）颜色空间。
        /// </summary>
        /// <param name="color"></param>
        /// <returns></returns>
        public static Controls.Hsb ToHsb(this Color color)
        {
            double r = color.R;
            double g = color.G;
            double b = color.B;
            double a = color.A;

            r /= 255;
            g /= 255;
            b /= 255;
            a /= 255;

            var rgb = new[] { r, g, b };
            var max = rgb.Max();
            var min = rgb.Min();
            var brightness = max;
            var hue = max;

            var delta = max - min;
            var saturation = max.IsCloseTo(0) ? 0 : delta / max;

            if (max.IsCloseTo(min))
            {
                hue = 0; // 无色，未定义
            }
            else
            {
                if (max.IsCloseTo(r))
                {
                    hue = (g - b) / delta + (g < b ? 6 : 0);
                }
                else if (max.IsCloseTo(g))
                {
                    hue = (b - r) / delta + 2;
                }
                else if (max.IsCloseTo(b))
                {
                    hue = (r - g) / delta + 4;
                }

                hue *= 60;
            }

            return new Hsb(hue, saturation, brightness, a);
        }
    }
}