Как создать блокирующее окно используя WinAPI?

#include <windows.h>
 
#define ErrorMsg(msg) MessageBox (NULL, msg, "Error!", MB_OK | MB_ICONERROR)
 
#define WND_DESKTOP_LOCK_CLASS   "my_wdlc"
#define WND_MESSAGE_CLASS        "my_wmc"
 
#define IDC_OK  1000
 
BOOL _RegisterClass (HINSTANCE, char *, WNDPROC, HBRUSH);
LRESULT CALLBACK WindowProcedure_DesktopLock (HWND, UINT, WPARAM, LPARAM);
LRESULT CALLBACK WindowProcedure_Message (HWND, UINT, WPARAM, LPARAM);
 
 
LRESULT CALLBACK WindowProcedure_DesktopLock (HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)
    {
         case WM_CREATE:
         {
              HWND hWindow = CreateWindowEx (0, WND_MESSAGE_CLASS, "Message",
                                             WS_OVERLAPPEDWINDOW & ~WS_MAXIMIZEBOX & ~WS_MINIMIZEBOX & ~WS_THICKFRAME,
                                             (GetSystemMetrics (SM_CXSCREEN) >> 1) - (400 >> 1),
                                             (GetSystemMetrics (SM_CYSCREEN) >> 1) - (200 >> 1),
                                             400, 200,
                                             hWnd, (HMENU) 0, GetModuleHandle (NULL), NULL);
              SetWindowLongPtr (hWindow, GWL_STYLE, GetWindowLongPtr (hWindow, GWL_STYLE) || WS_CAPTION);
              if (!hWindow)
                   ErrorMsg ("Window Creation Failed! #2");
              ShowWindow (hWindow, SW_SHOW);
         }
         break;
         
         case WM_DESTROY:
              PostQuitMessage (0);
              break;
    }
    return DefWindowProc (hWnd, message, wParam, lParam);
}
 
LRESULT CALLBACK WindowProcedure_Message (HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    static HFONT hBigFont;
    switch (message)
    {
         case WM_CREATE:
         {
              LOGFONT lf;
              ZeroMemory (&lf, sizeof (lf));
              lf.lfHeight = 100;
              hBigFont = CreateFontIndirect (&lf);
              
              CreateWindowEx (0, "button", "OK", WS_VISIBLE | WS_CHILD | BS_OWNERDRAW, 290, 170, 100, 20,
                              hWnd, (HMENU) IDC_OK, NULL, NULL);
         }
         break;
         
         case WM_COMMAND:
         {
              if (LOWORD (wParam) == IDC_OK)
                   DestroyWindow (hWnd);
         }
         break;
         
         case WM_PAINT:
         {
              PAINTSTRUCT ps;
              HDC hDC = BeginPaint (hWnd, &ps);
              SetBkMode (hDC, TRANSPARENT);
              
              HFONT hOldFont = (HFONT) SelectObject (hDC, (HFONT) hBigFont);
              SetTextColor (hDC, RGB (255, 255, 200));
              TextOut (hDC, 20, 30, "Message", strlen ("Message"));
              
              SelectObject (hDC, (HFONT) hOldFont);
              EndPaint (hWnd, &ps);
         }
         break;
         
         case WM_DRAWITEM:
         {
              LPDRAWITEMSTRUCT lpdis = (LPDRAWITEMSTRUCT)lParam;
              if (lpdis -> CtlType & ODT_BUTTON)
              {
                   switch (lpdis -> CtlID)
                   {
                        case IDC_OK:
                        {
                             RECT rc;
                             SetRect (&rc, lpdis -> rcItem.left, lpdis -> rcItem.top, lpdis -> rcItem.right, lpdis -> rcItem.bottom);
                             if (lpdis -> itemState & ODS_SELECTED)
                                  FillRect (lpdis -> hDC, &rc, (HBRUSH) GetStockObject (DKGRAY_BRUSH));
                             else
                                  FillRect (lpdis -> hDC, &rc, (HBRUSH) GetStockObject (LTGRAY_BRUSH));
                             SetBkMode (lpdis -> hDC, TRANSPARENT);
                             SetTextColor (lpdis -> hDC, RGB (200, 50, 50));
                             TextOut (lpdis -> hDC, lpdis -> rcItem.left + 40, lpdis -> rcItem.top + 2, "OK", 2);
                        }
                        break;
                   }
              }
         }
         break;
         
         case WM_DESTROY:
              PostQuitMessage (0);
              break;
    }
    return DefWindowProc (hWnd, message, wParam, lParam);
}
 
BOOL _RegisterClass (HINSTANCE hInstance, char *szClassName, WNDPROC WndProc, HBRUSH hBrush)
{
    WNDCLASSEX wc;
    wc.cbSize        = sizeof (wc);
    wc.style         = CS_HREDRAW | CS_VREDRAW;
    wc.lpfnWndProc   = WndProc;
    wc.cbClsExtra    = 0;
    wc.cbWndExtra    = 0;
    wc.hInstance     = hInstance;
    wc.hIcon         = LoadIcon (NULL, IDI_APPLICATION);
    wc.hCursor       = LoadCursor (NULL, IDC_ARROW);
    wc.hbrBackground = hBrush;
    wc.lpszMenuName  = NULL;
    wc.lpszClassName = szClassName;
    wc.hIconSm       = LoadIcon (NULL, IDI_APPLICATION);
    return RegisterClassEx (&wc);
}
 
int WINAPI WinMain (HINSTANCE hThisInstance, HINSTANCE hPrevInstance, LPSTR lpszArgument, int nFunsterStil)
{
    if (!_RegisterClass (hThisInstance, WND_DESKTOP_LOCK_CLASS, WindowProcedure_DesktopLock, (HBRUSH) GetStockObject (GRAY_BRUSH)))
    {
         ErrorMsg ("Window Registration Failed! #1");
         return 0;
    }
    
    if (!_RegisterClass (hThisInstance, WND_MESSAGE_CLASS, WindowProcedure_Message, (HBRUSH) GetStockObject (GRAY_BRUSH)))
    {
         UnregisterClass (WND_DESKTOP_LOCK_CLASS, hThisInstance);
         ErrorMsg ("Window Registration Failed! #2");
         return 0;
    }
    
    HWND hWnd = CreateWindowEx (WS_EX_LAYERED | WS_EX_TOPMOST, WND_DESKTOP_LOCK_CLASS, "DesktopLock",
                                WS_OVERLAPPEDWINDOW & ~WS_MAXIMIZEBOX & ~WS_MINIMIZEBOX & ~WS_THICKFRAME,
                                CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, HWND_DESKTOP, (HMENU) 0, hThisInstance, NULL);
    if (!hWnd)
    {
         UnregisterClass (WND_DESKTOP_LOCK_CLASS, hThisInstance);
         UnregisterClass (WND_MESSAGE_CLASS, hThisInstance);
         ErrorMsg ("Window Creation Failed! #1");
         return 0;
    }
    SetWindowLongPtr (hWnd, GWL_STYLE, GetWindowLongPtr (hWnd, GWL_STYLE) || WS_CAPTION);
    
    HMODULE hModule = GetModuleHandle ("user32.dll");
    if (!hModule)
    {
         UnregisterClass (WND_DESKTOP_LOCK_CLASS, hThisInstance);
         UnregisterClass (WND_MESSAGE_CLASS, hThisInstance);
         ErrorMsg ("user32.dll not found!");
         return 0;
    }
    typedef BOOL (WINAPI *SetLayered) (HWND hwnd, COLORREF crKey, BYTE bAlpha, DWORD dwFlags);
    SetLayered _SetLayeredWindowAttributes = (SetLayered) GetProcAddress (hModule, "SetLayeredWindowAttributes");
    if (!_SetLayeredWindowAttributes)
    {
         FreeLibrary (hModule);
         UnregisterClass (WND_DESKTOP_LOCK_CLASS, hThisInstance);
         UnregisterClass (WND_MESSAGE_CLASS, hThisInstance);
         ErrorMsg ("The entry point to the procedure SetLayeredWindowAttributes was not found in the DLL user32.dll");
         return 0;
    }
    
    _SetLayeredWindowAttributes (hWnd, 0, 100, 0x02);
    
    ShowWindow (hWnd, SW_SHOWMAXIMIZED);
    UpdateWindow (hWnd);
    
    MSG msg;
    while (GetMessage (&msg, NULL, 0, 0))
    {
         TranslateMessage (&msg);
         DispatchMessage (&msg);
    }
    
    FreeLibrary (hModule);
    UnregisterClass (WND_DESKTOP_LOCK_CLASS, hThisInstance);
    UnregisterClass (WND_MESSAGE_CLASS, hThisInstance);
    return (int) msg.wParam;
}