GetWndProc.cs

// Wrap a 16-bit virtual window procedure in a managed delegate that
// when invoked will call the virtual proc.  
public IntPtr GetWndProc32(uint lpfnWndProc)
{
    if (lpfnWndProc == 0)
        return IntPtr.Zero;

    // Check if already wrapped
    IntPtr wndProc32 = WndProcMap.To32(lpfnWndProc);
    if (wndProc32!=IntPtr.Zero)
        return wndProc32;

    // Nope, create one
    Win32.WNDPROC wndProc32Managed = (hWnd, message, wParam, lParam) =>
    {
        return CallWndProc16from32(lpfnWndProc, hWnd, message, wParam, lParam);
    };

    // Connect
    return WndProcMap.Connect(wndProc32Managed, lpfnWndProc);
}

// Create a 16-bit thunk that will call a Win32 window procedure
public uint GetWndProc16(IntPtr lpfnWndProc32, bool create = true)
{
    if (lpfnWndProc32 == IntPtr.Zero)
        return 0;

    // Already wrapped?
    uint wndProc16 = WndProcMap.To16(lpfnWndProc32);
    if (wndProc16 != 0)
        return wndProc16;

    if (!create)
        return 0;

    // Create a 16-bit thunk that calls it
    wndProc16 = _machine.CreateSystemThunk(() =>
    {
        ushort hWnd16 = _machine.ReadWord(_machine.ss, (ushort)(_machine.sp + 12));
        ushort message16 = _machine.ReadWord(_machine.ss, (ushort)(_machine.sp + 10));
        ushort wParam16 = _machine.ReadWord(_machine.ss, (ushort)(_machine.sp + 8));
        uint lParam16 = _machine.ReadDWord(_machine.ss, (ushort)(_machine.sp + 4));
   
       _machine.dxax = CallWndProc32from16(lpfnWndProc32, hWnd16, message16, wParam16, lParam16);

    }, 10, false, "WndProc32");      // hWnd = 2, msg = 2, wParam = 2, lParam = 4

    // Update maps
    WndProcMap.Connect(lpfnWndProc32, wndProc16);

    // Done
    return wndProc16;
}