HaloPixelToolBox

using System.Drawing;
using System.Drawing.Drawing2D;
using System.Runtime.Versioning;

namespace HaloPixelToolBox.Backend.Utilities;

[SupportedOSPlatform("windows")]
public static class AvatarGenerator
{
    /// <summary>
    /// 根据中文姓氏生成头像图片（白字 + 随机深色背景）
    /// </summary>
    /// <param name="surname">中文姓氏</param>
    /// <param name="size">头像边长（像素）</param>
    /// <returns>Bitmap 对象</returns>
    public static Bitmap CreateAvatar(string surname, int size = 128)
    {
        if (string.IsNullOrWhiteSpace(surname))
            surname = "?";

        var initial = surname.Trim()[0].ToString();

        var bg = ColorFromName(initial);
        if (!IsDarkEnough(bg))
            bg = Darken(bg, 0.3);

        var bmp = new Bitmap(size, size);
        using var g = Graphics.FromImage(bmp);
        g.SmoothingMode = SmoothingMode.AntiAlias;
        g.Clear(Color.Transparent);

        using (var brush = new SolidBrush(bg))
        {
            g.FillEllipse(brush, 0, 0, size, size);
        }

        var fontSize = size * 0.45f;
        using var font = new Font("Microsoft YaHei", fontSize, FontStyle.Bold, GraphicsUnit.Pixel);
        using var sf = new StringFormat();
        sf.Alignment = StringAlignment.Center;
        sf.LineAlignment = StringAlignment.Center;
        using var textBrush = new SolidBrush(Color.White);
        var rect = new Rectangle(0, 0, size, size);
        g.DrawString(initial, font, textBrush, rect, sf);

        return bmp;
    }

    private static Color ColorFromName(string name)
    {
        var hash = name.GetHashCode();
        var rnd = new Random(hash);
        return Color.FromArgb(255,
            rnd.Next(64, 192),
            rnd.Next(64, 192),
            rnd.Next(64, 192));
    }

    private static bool IsDarkEnough(Color c)
    {
        var lum = (0.2126 * c.R + 0.7152 * c.G + 0.0722 * c.B) / 255.0;
        return lum < 0.6;
    }

    private static Color Darken(Color c, double factor)
    {
        return Color.FromArgb(c.A,
            (int)(c.R * (1 - factor)),
            (int)(c.G * (1 - factor)),
            (int)(c.B * (1 - factor)));
    }
}