FontDialogEx.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Diagnostics;
using System.Drawing;
using System.Runtime.InteropServices;
using System.Windows.Forms;

[DesignerCategory("code")]
public class FontDialogEx : FontDialog
{
    public FontDialogEx() { }

    // スタイル名
    private enum WeightStyles
    {
        THIN = 100,
        EXTRALIGHT = 200,
        ULTRALIGHT = 200,
        LIGHT = 300,
        SEMILIGHT = 350,
        NORMAL = 400,
        REGULAR = 400,
        MEDIUM = 500,
        SEMIBOLD = 600,
        DEMIBOLD = 600,
        BOLD = 700,
        EXTRABOLD = 800,
        ULTRABOLD = 800,
        HEAVY = 900,
        BLACK = 900
    }

    // ダイアログで選択したとき フォント名と lfWeight の組み合わせを登録して次回から使用する。
    // 既知のフォントはあらかじめ登録しておく
    private static readonly Dictionary<string, int> dicWeight
                   = new Dictionary<string, int>(StringComparer.OrdinalIgnoreCase) {
                       { "Nirmala UI Semilight", 350 },
                       { "Microsoft JhengHei Light", 290 },
                       { "Microsoft JhengHei UI Light", 290 },
                       { "Segoe UI Light", 300 },
                       { "Segoe UI Semibold", 600 },
                       { "Segoe UI Black", 900 }
                   };

    private static NativeMethods.LOGFONT GetLogFont(Font font) {
        // 既知のフォント名から lfWeight を設定する
        var logFont = new NativeMethods.LOGFONT();
        font.ToLogFont(logFont);
        lock (dicWeight) {
            if (dicWeight.TryGetValue(logFont.lfFaceName, out int weight)) {
                logFont.lfWeight = weight;
                return logFont;
            }
        }
        // フォント名からスタイルを検索して lfWeight を設定する
        var faceName = logFont.lfFaceName.ToUpper();
        foreach (WeightStyles style in Enum.GetValues(typeof(WeightStyles))) {
            if (faceName.IndexOf(" " + style.ToString()) >= 0) {
                logFont.lfWeight = (int)style;
                break;
            }
        }
        return logFont;
    }

    protected override bool RunDialog(IntPtr hWndOwner) {
        var hookProcPtr = new NativeMethods.WndProc(HookProc);
        var cf = new NativeMethods.CHOOSEFONT();
        var logFontPtr = IntPtr.Zero;
        try {
            logFontPtr = Marshal.AllocCoTaskMem(Marshal.SizeOf(typeof(NativeMethods.LOGFONT)));
            var logFont = GetLogFont(Font);
            Marshal.StructureToPtr(logFont, logFontPtr, false);
            cf.hwndOwner = hWndOwner;
            cf.hDC = IntPtr.Zero;
            cf.lpLogFont = logFontPtr;
            cf.Flags = Options | NativeMethods.CF_INITTOLOGFONTSTRUCT | NativeMethods.CF_ENABLEHOOK;
            if (MinSize > 0 || MaxSize > 0) {
                cf.Flags |= NativeMethods.CF_LIMITSIZE;
            }
            if (ShowColor || ShowEffects) {
                cf.rgbColors = ColorTranslator.ToWin32(Color);
            } else {
                cf.rgbColors = ColorTranslator.ToWin32(SystemColors.ControlText);
            }

            cf.lpfnHook = hookProcPtr;
            cf.hInstance = NativeMethods.GetModuleHandle(null);
            cf.nSizeMin = MinSize;
            if (MaxSize == 0) {
                cf.nSizeMax = int.MaxValue;
            } else {
                cf.nSizeMax = MaxSize;
            }

            if (!NativeMethods.ChooseFont(cf)) return false;

            logFont = Marshal.PtrToStructure<NativeMethods.LOGFONT>(logFontPtr);
            if (logFont.lfFaceName != null && logFont.lfFaceName.Length > 0) {
                UpdateFont(logFont);
                UpdateColor(cf.rgbColors);
            }
            return true;

        } finally {
            if (logFontPtr != IntPtr.Zero) {
                Marshal.FreeCoTaskMem(logFontPtr);
            }
        }
    }

    protected override IntPtr HookProc(IntPtr hWnd, int msg, IntPtr wparam, IntPtr lparam) {
        switch (msg) {
            case NativeMethods.WM_COMMAND:
                if ((int)wparam == 0x402) {
                    NativeMethods.LOGFONT lf = new NativeMethods.LOGFONT();
                    NativeMethods.SendMessage(hWnd, NativeMethods.WM_CHOOSEFONT_GETLOGFONT, 0, lf);
                    UpdateFont(lf);
                }
                break;
        }
        return base.HookProc(hWnd, msg, wparam, lparam);
    }

    private void UpdateFont(NativeMethods.LOGFONT logFont) {
        // LOGFONT から Font を作成する
        Font = Font.FromLogFont(logFont);

        // Font から LOGFONT を取り出す
        var gdipLogFont = GetLogFont(Font);

        Debug.Print($"{logFont.lfFaceName} {logFont.lfWeight}:{gdipLogFont.lfWeight}");

        // lfWeight が違う場合は保存する
        if (gdipLogFont.lfWeight != logFont.lfWeight) {
            lock (dicWeight) {
                dicWeight[logFont.lfFaceName] = logFont.lfWeight;
            }
        }
    }

    private void UpdateColor(int rgb) {
        if (ColorTranslator.ToWin32(Color) != rgb) {
            Color = ColorTranslator.FromOle(rgb);
        }
    }
}

internal static class NativeMethods
{
    public const int
        WM_COMMAND = 0x0111,
        WM_USER = 0x0400,
        WM_CHOOSEFONT_GETLOGFONT = WM_USER + 1;

    public const int
        CF_INITTOLOGFONTSTRUCT = 0x00000040,
        CF_ENABLEHOOK = 0x00000008,
        CF_LIMITSIZE = 0x00002000;

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
    public class LOGFONT
    {
        public int lfHeight;
        public int lfWidth;
        public int lfEscapement;
        public int lfOrientation;
        public int lfWeight;
        public byte lfItalic;
        public byte lfUnderline;
        public byte lfStrikeOut;
        public byte lfCharSet;
        public byte lfOutPrecision;
        public byte lfClipPrecision;
        public byte lfQuality;
        public byte lfPitchAndFamily;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]
        public string lfFaceName;

        public LOGFONT() { }

        public LOGFONT(LOGFONT lf) {
            lfHeight = lf.lfHeight;
            lfWidth = lf.lfWidth;
            lfEscapement = lf.lfEscapement;
            lfOrientation = lf.lfOrientation;
            lfWeight = lf.lfWeight;
            lfItalic = lf.lfItalic;
            lfUnderline = lf.lfUnderline;
            lfStrikeOut = lf.lfStrikeOut;
            lfCharSet = lf.lfCharSet;
            lfOutPrecision = lf.lfOutPrecision;
            lfClipPrecision = lf.lfClipPrecision;
            lfQuality = lf.lfQuality;
            lfPitchAndFamily = lf.lfPitchAndFamily;
            lfFaceName = lf.lfFaceName;
        }
    }

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
    public class CHOOSEFONT
    {
        public int lStructSize = Marshal.SizeOf(typeof(CHOOSEFONT));
        public IntPtr hwndOwner;
        public IntPtr hDC;
        public IntPtr lpLogFont;
        public int iPointSize = 0;
        public int Flags;
        public int rgbColors;
        public IntPtr lCustData = IntPtr.Zero;
        public WndProc lpfnHook;
        public string lpTemplateName = null;
        public IntPtr hInstance;
        public string lpszStyle = null;
        public short nFontType = 0;
        public short ___MISSING_ALIGNMENT__ = 0;
        public int nSizeMin;
        public int nSizeMax;
    }

    [DllImport("comdlg32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    public static extern bool ChooseFont([In, Out] CHOOSEFONT cf);

    [DllImport("Kernel32.dll", CharSet = CharSet.Auto)]
    public static extern IntPtr GetModuleHandle(string modName);

    public delegate IntPtr WndProc(IntPtr hWnd, int msg, IntPtr wParam, IntPtr lParam);

    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    public static extern IntPtr SendMessage(IntPtr hWnd, int msg, int wParam, [In, Out] LOGFONT lParam);
}