native splash screen when using native aot without wpf or win forms

SplashScreen.cs

using System.ComponentModel;
using static NativeApi;
public class SplashScreen : IDisposable
{
    private ushort _wndClass;
    private IntPtr _hwnd;
    private const string CLASS_NAME = "SplashScreen";
    private Bitmap _bitmap;
    private static HandleRef nullHandle = new HandleRef(null, IntPtr.Zero);
    private WndProc? proc;
    public SplashScreen(FileInfo bitmapFile)
    {
        if (!bitmapFile.Exists)
            throw new FileNotFoundException($"File '{bitmapFile.FullName}' is not found");
        _bitmap = (Bitmap)Bitmap.FromFile(bitmapFile.FullName);
    }

    public void Show(bool topmost)
    {
        if (isDisposed)
            throw new ObjectDisposedException("");
        _hwnd = CreateWindow(_bitmap.GetHbitmap(), _bitmap.Width, _bitmap.Height, topmost);
    }

    public void Hide() 
        => Dispose();


    private nint CreateWindow(nint hBitmap, int width, int height, bool topMost)
    {
        proc = new WndProc(DefWindowProc);
        var wndClass = new WNDCLASSEX();
        wndClass.cbSize = 80;
        wndClass.style = 3; /* CS_HREDRAW | CS_VREDRAW */
        wndClass.hInstance = IntPtr.Zero;
        wndClass.hCursor = IntPtr.Zero;
        wndClass.lpszClassName = CLASS_NAME;
        wndClass.lpszMenuName = string.Empty;
        wndClass.lpfnWndProc = proc;

        _wndClass = IntRegisterClassEx(wndClass);

        var screenWidth = GetSystemMetrics(SystemMetric.SM_CXSCREEN);
        var screenHeight = GetSystemMetrics(SystemMetric.SM_CYSCREEN);
        var x = (screenWidth - width) / 2;
        var y = (screenHeight - height) / 2;

        var windowCreateFlags =
            WS_EX_WINDOWEDGE |
            WS_EX_TOOLWINDOW |
            WS_EX_LAYERED |
            (topMost ? WS_EX_TOPMOST : 0);

        var hWnd =  CreateWindowEx(
            windowCreateFlags,
            CLASS_NAME, "",
            unchecked((int)( WindowStyles.WS_POPUP |  WindowStyles.WS_VISIBLE)),
            x, y, width, height,
            nullHandle, nullHandle, /*new HandleRef(null, _hInstance)*/ nullHandle, IntPtr.Zero);

        var hScreenDC = GetDC(new HandleRef());
        var memDC = CreateCompatibleDC(new HandleRef(null, hScreenDC));
        var hOldBitmap = SelectObject(new HandleRef(null, memDC), hBitmap);
 
        var newSize = new NativeApi.Size(width, height);
        var newLocation = new NativeApi.Point(x, y);
        var sourceLocation = new NativeApi.Point(0, 0);
        var _blendFunc = new BLENDFUNCTION();
        _blendFunc.BlendOp = AC_SRC_OVER;
        _blendFunc.BlendFlags = 0;
        _blendFunc.SourceConstantAlpha = 255;
        _blendFunc.AlphaFormat = 1; /*AC_SRC_ALPHA*/
 
        var result = UpdateLayeredWindow(hWnd, hScreenDC, ref newLocation, ref newSize,
            memDC, ref sourceLocation, 0, ref _blendFunc, ULW_ALPHA);
 
        SelectObject(new HandleRef(null, memDC), hOldBitmap);
        ReleaseDC(new HandleRef(), new HandleRef(null, memDC));
        ReleaseDC(new HandleRef(), new HandleRef(null, hScreenDC));
 
        if (result == Bool.False)
            throw new Win32Exception(Marshal.GetHRForLastWin32Error());

        return hWnd;
    }

    private void ReleaseUnmanagedResources()
    {
        SetActiveWindow(new HandleRef(null, _hwnd));
        IntDestroyWindow(new HandleRef(null, _hwnd));
        IntUnregisterClass(new IntPtr(_wndClass), IntPtr.Zero);
    }

    private void Dispose(bool disposing)
    {
        ReleaseUnmanagedResources();
        if (disposing) _bitmap.Dispose();
        isDisposed = true;
    }

    private bool isDisposed = false;
    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }

    ~SplashScreen() 
        => Dispose(false);
}

win32.cs

public class NativeApi
{
    public enum Bool: int
    {
        @False = 0,
        @True = 1
    }
    public struct Point
    {
        public int x;

        public int y;


        public Point(int x, int y)
        {
            this.x = x;
            this.y = y;
        }
    }

    public struct Size
    {
        public int cx;

        public int cy;


        public Size(int cx, int cy)
        {
            this.cx = cx;
            this.cy = cy;
        }
    }

    public enum Protection
    {
        PAGE_NOACCESS = 0x01,
        PAGE_READONLY = 0x02,
        PAGE_READWRITE = 0x04,
        PAGE_WRITECOPY = 0x08,
        PAGE_EXECUTE = 0x10,
        PAGE_EXECUTE_READ = 0x20,
        PAGE_EXECUTE_READWRITE = 0x40,
        PAGE_EXECUTE_WRITECOPY = 0x80,
        PAGE_GUARD = 0x100,
        PAGE_NOCACHE = 0x200,
        PAGE_WRITECOMBINE = 0x400
    }

    public struct BLENDFUNCTION
    {
        public byte BlendOp;
        public byte BlendFlags;
        public byte SourceConstantAlpha;
        public byte AlphaFormat;
    }
    
    public const int AC_SRC_OVER  = 0x00000000;
    public const int ULW_COLORKEY = 0x00000001;
    public const int ULW_ALPHA    = 0x00000002;
    public const int ULW_OPAQUE   = 0x00000004;

    public const byte AC_SRC_ALPHA = 1;
    public const int WS_POPUP = unchecked((int)0x80000000);

    public const int WS_EX_LAYERED = 0x00080000,
        WS_EX_WINDOWEDGE = 0x00000100,
        WS_EX_TOOLWINDOW = 0x00000080,
        WS_EX_TOPMOST = 0x00000008;

    [DllImport("kernel32.dll")]
    internal static extern bool FlushInstructionCache(IntPtr hProcess, IntPtr lpBaseAddress,
        UIntPtr dwSize);

    [DllImport("kernel32", CharSet = CharSet.Ansi, ExactSpelling = true, SetLastError = true)]
    internal static extern IntPtr GetProcAddress(IntPtr hModule, string procName);

    [DllImport("kernel32", SetLastError = true, CharSet = CharSet.Ansi)]
    internal static extern IntPtr LoadLibrary([MarshalAs(UnmanagedType.LPStr)]string lpFileName);
    
    [DllImport("kernel32.dll")]
    internal static extern void Sleep(uint dwMilliseconds);

    [DllImport("kernel32.dll", SetLastError = true)]
    internal static extern bool VirtualProtect(IntPtr lpAddress, uint dwSize,
        Protection flNewProtect, out Protection lpflOldProtect);

    [DllImport("user32.dll", CharSet = CharSet.Unicode, EntryPoint = "DefWindowProcW")]
    public static extern IntPtr DefWindowProc(IntPtr hWnd, Int32 Msg, IntPtr wParam, IntPtr lParam);

    public delegate IntPtr WndProc(IntPtr hWnd, Int32 msg, IntPtr wParam, IntPtr lParam);

    [DllImport("user32.dll", EntryPoint="RegisterClassEx", CharSet=CharSet.Unicode, SetLastError=true, BestFitMapping=false)]
    internal static extern UInt16 IntRegisterClassEx(WNDCLASSEX wc_d);

    [DllImport("user32.dll", SetLastError = true)]
    public static extern IntPtr SetActiveWindow(HandleRef hWnd);

    [DllImport("user32.dll", SetLastError = true, EntryPoint="DestroyWindow", CharSet=CharSet.Auto)]
    public static extern bool IntDestroyWindow(HandleRef hWnd);

    [DllImport("user32.dll", EntryPoint="UnregisterClass",CharSet = CharSet.Auto, SetLastError = true, BestFitMapping=false)]
    internal static extern int IntUnregisterClass(IntPtr atomString /*lpClassName*/ , IntPtr hInstance);

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
    public struct WNDCLASSEX
    {
        [MarshalAs(UnmanagedType.U4)]
        public int cbSize = 80;
        [MarshalAs(UnmanagedType.U4)]
        public int style;
        public WndProc lpfnWndProc; // not WndProc
        public int cbClsExtra;
        public int cbWndExtra;
        public IntPtr hInstance;
        public IntPtr hIcon;
        public IntPtr hCursor;
        public IntPtr hbrBackground;
        public string lpszMenuName;
        public string lpszClassName;
        public IntPtr hIconSm;

        public WNDCLASSEX()
        {
        }
    }


    [DllImport("user32.dll")]
    [return: MarshalAs(UnmanagedType.U2)]
    static extern short RegisterClassEx([In] ref WNDCLASSEX lpwcx);


    [DllImport("user32.dll")]
    public extern static Bool UpdateLayeredWindow(IntPtr handle, IntPtr hdcDst, ref Point pptDst, ref Size psize, IntPtr hdcSrc, ref Point pprSrc, int crKey, ref BLENDFUNCTION pblend, int dwFlags);

    [DllImport("user32.dll")]
    public extern static IntPtr GetDC(HandleRef handle);

    [DllImport("user32.dll", ExactSpelling=true)]
    public extern static int ReleaseDC(HandleRef handle, HandleRef hDC);

    [DllImport("gdi32.dll")]
    public extern static IntPtr CreateCompatibleDC(HandleRef hDC);

    [DllImport("gdi32.dll")]
    public extern static Bool DeleteDC(HandleRef hdc);

    [DllImport("gdi32.dll")]
    public extern static IntPtr SelectObject(HandleRef hDC, IntPtr hObject);

    [DllImport("gdi32.dll")]
    public extern static Bool DeleteObject(HandleRef hObject);

    [DllImport("user32.dll", EntryPoint = "CreateWindowEx", CharSet = CharSet.Unicode)]
    internal static extern IntPtr CreateWindowEx(int dwExStyle,
        string lpszClassName,
        string lpszWindowName,
        int style,
        int x, int y,
        int width, int height,
        HandleRef hwndParent,
        HandleRef hMenu,
        HandleRef hInst,
        [MarshalAs(UnmanagedType.AsAny)] object pvParam);

    [DllImport("user32.dll")]
    public static extern int GetSystemMetrics(SystemMetric smIndex);


    public enum SystemMetric
    {
        SM_CXSCREEN            = 0,  // 0x00
        SM_CYSCREEN            = 1,  // 0x01
        SM_CXVSCROLL           = 2,  // 0x02
        SM_CYHSCROLL           = 3,  // 0x03
        SM_CYCAPTION           = 4,  // 0x04
        SM_CXBORDER            = 5,  // 0x05
        SM_CYBORDER            = 6,  // 0x06
        SM_CXDLGFRAME          = 7,  // 0x07
        SM_CXFIXEDFRAME        = 7,  // 0x07
        SM_CYDLGFRAME          = 8,  // 0x08
        SM_CYFIXEDFRAME        = 8,  // 0x08
        SM_CYVTHUMB            = 9,  // 0x09
        SM_CXHTHUMB            = 10, // 0x0A
        SM_CXICON              = 11, // 0x0B
        SM_CYICON              = 12, // 0x0C
        SM_CXCURSOR            = 13, // 0x0D
        SM_CYCURSOR            = 14, // 0x0E
        SM_CYMENU              = 15, // 0x0F
        SM_CXFULLSCREEN        = 16, // 0x10
        SM_CYFULLSCREEN        = 17, // 0x11
        SM_CYKANJIWINDOW           = 18, // 0x12
        SM_MOUSEPRESENT        = 19, // 0x13
        SM_CYVSCROLL           = 20, // 0x14
        SM_CXHSCROLL           = 21, // 0x15
        SM_DEBUG               = 22, // 0x16
        SM_SWAPBUTTON          = 23, // 0x17
        SM_CXMIN               = 28, // 0x1C
        SM_CYMIN               = 29, // 0x1D
        SM_CXSIZE              = 30, // 0x1E
        SM_CYSIZE              = 31, // 0x1F
        SM_CXSIZEFRAME         = 32, // 0x20
        SM_CXFRAME             = 32, // 0x20
        SM_CYSIZEFRAME         = 33, // 0x21
        SM_CYFRAME             = 33, // 0x21
        SM_CXMINTRACK          = 34, // 0x22
        SM_CYMINTRACK          = 35, // 0x23
        SM_CXDOUBLECLK         = 36, // 0x24
        SM_CYDOUBLECLK         = 37, // 0x25
        SM_CXICONSPACING           = 38, // 0x26
        SM_CYICONSPACING           = 39, // 0x27
        SM_MENUDROPALIGNMENT       = 40, // 0x28
        SM_PENWINDOWS          = 41, // 0x29
        SM_DBCSENABLED         = 42, // 0x2A
        SM_CMOUSEBUTTONS           = 43, // 0x2B
        SM_SECURE              = 44, // 0x2C
        SM_CXEDGE              = 45, // 0x2D
        SM_CYEDGE              = 46, // 0x2E
        SM_CXMINSPACING        = 47, // 0x2F
        SM_CYMINSPACING        = 48, // 0x30
        SM_CXSMICON            = 49, // 0x31
        SM_CYSMICON            = 50, // 0x32
        SM_CYSMCAPTION         = 51, // 0x33
        SM_CXSMSIZE            = 52, // 0x34
        SM_CYSMSIZE            = 53, // 0x35
        SM_CXMENUSIZE          = 54, // 0x36
        SM_CYMENUSIZE          = 55, // 0x37
        SM_ARRANGE             = 56, // 0x38
        SM_CXMINIMIZED         = 57, // 0x39
        SM_CYMINIMIZED         = 58, // 0x3A
        SM_CXMAXTRACK          = 59, // 0x3B
        SM_CYMAXTRACK          = 60, // 0x3C
        SM_CXMAXIMIZED         = 61, // 0x3D
        SM_CYMAXIMIZED         = 62, // 0x3E
        SM_NETWORK             = 63, // 0x3F
        SM_CLEANBOOT           = 67, // 0x43
        SM_CXDRAG              = 68, // 0x44
        SM_CYDRAG              = 69, // 0x45
        SM_SHOWSOUNDS          = 70, // 0x46
        SM_CXMENUCHECK         = 71, // 0x47
        SM_CYMENUCHECK         = 72, // 0x48
        SM_SLOWMACHINE         = 73, // 0x49
        SM_MIDEASTENABLED          = 74, // 0x4A
        SM_MOUSEWHEELPRESENT       = 75, // 0x4B
        SM_XVIRTUALSCREEN          = 76, // 0x4C
        SM_YVIRTUALSCREEN          = 77, // 0x4D
        SM_CXVIRTUALSCREEN         = 78, // 0x4E
        SM_CYVIRTUALSCREEN         = 79, // 0x4F
        SM_CMONITORS           = 80, // 0x50
        SM_SAMEDISPLAYFORMAT       = 81, // 0x51
        SM_IMMENABLED          = 82, // 0x52
        SM_CXFOCUSBORDER           = 83, // 0x53
        SM_CYFOCUSBORDER           = 84, // 0x54
        SM_TABLETPC            = 86, // 0x56
        SM_MEDIACENTER         = 87, // 0x57
        SM_STARTER             = 88, // 0x58
        SM_SERVERR2            = 89, // 0x59
        SM_MOUSEHORIZONTALWHEELPRESENT = 91, // 0x5B
        SM_CXPADDEDBORDER          = 92, // 0x5C
        SM_DIGITIZER           = 94, // 0x5E
        SM_MAXIMUMTOUCHES          = 95, // 0x5F

        SM_REMOTESESSION           = 0x1000, // 0x1000
        SM_SHUTTINGDOWN        = 0x2000, // 0x2000
        SM_REMOTECONTROL           = 0x2001, // 0x2001


        SM_CONVERTIBLESLATEMODE    = 0x2003,
        SM_SYSTEMDOCKED        = 0x2004,
    }

    [Flags]
    public enum WindowStyles : uint
    {
        WS_BORDER = 0x800000,
        WS_CAPTION = 0xc00000,
        WS_CHILD = 0x40000000,
        WS_CLIPCHILDREN = 0x2000000,
        WS_CLIPSIBLINGS = 0x4000000,
        WS_DISABLED = 0x8000000,
        WS_DLGFRAME = 0x400000,
        WS_GROUP = 0x20000,
        WS_HSCROLL = 0x100000,
        WS_MAXIMIZE = 0x1000000,
        WS_MAXIMIZEBOX = 0x10000,
        WS_MINIMIZE = 0x20000000,
        WS_MINIMIZEBOX = 0x20000,
        WS_OVERLAPPED = 0x0,
        WS_OVERLAPPEDWINDOW = WS_OVERLAPPED | WS_CAPTION | WS_SYSMENU | WS_SIZEFRAME | WS_MINIMIZEBOX | WS_MAXIMIZEBOX,
        WS_POPUP = 0x80000000u,
        WS_POPUPWINDOW = WS_POPUP | WS_BORDER | WS_SYSMENU,
        WS_SIZEFRAME = 0x40000,
        WS_SYSMENU = 0x80000,
        WS_TABSTOP = 0x10000,
        WS_VISIBLE = 0x10000000,
        WS_VSCROLL = 0x200000
    }
}