#include <windows.h>

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow) 
{
    static TCHAR     szAppName[] = TEXT("BlockOut2"); 
    HWND             hwnd; 
    MSG              msg; 
    WNDCLASS         wndclass;

    wndclass.style          
 
= CS_HREDRAW | CS_VREDRAW;
    wndclass.lpfnWndProc    = WndProc;
    wndclass.cbClsExtra     = 0;
    wndclass.cbWndExtra     = 0;
    wndclass.hInstance      = hInstance;
    wndclass.hIcon          = LoadIcon(NULL, IDI_APPLICATION);
    wndclass.hCursor        = LoadCursor(NULL, IDC_ARROW);
    wndclass.hbrBackground  
 
= (HBRUSH)GetStockObject(WHITE_BRUSH);
    wndclass.lpszMenuName   = NULL;
    wndclass.lpszClassName  = szAppName;

    if(!RegisterClass(&wndclass)) {
        MessageBox(NULL, TEXT("This program requires Windows NT !"), szAppName, MB_ICONERROR);
        return 0;
    }

    hwnd = CreateWindow(szAppName, TEXT("
 
Mouse Button & Capture Demo"),
                        WS_OVERLAPPEDWINDOW,
                        CW_USEDEFAULT, CW_USEDEFAULT,
                        CW_USEDEFAULT, CW_USEDEFAULT,
                        NULL, NULL, hInstance, NULL);

    ShowWindow(hwnd, iCmdShow);
    UpdateWindow(hwnd);

    while(GetMessage(&msg, NULL, 0, 0))
    { 
        TranslateMessage(&msg); 
        DispatchMessage(&msg); 
    }
    return msg.wParam;
}

void DrawBoxOutline(HWND hwnd, POINT ptBeg, POINT ptEnd)
{
    HDC hdc;
    hdc = GetDC(hwnd);
    
    SetROP2(hdc, R2_NOT);
    SelectObject(hdc, GetStockObject(NULL_BRUSH));
    Rectangle(hdc, ptBeg.x, ptBeg.y, ptEnd.x, ptEnd.y);
    
    ReleaseDC(hwnd, hdc);    
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam) 
{
    static BOOL        fBlocking, fValidBox;
    static POINT       ptBeg, ptEnd, ptBoxBeg, ptBoxEnd;
    HDC                hdc;
    PAINTSTRUCT        ps;
    
    switch(message) 
    {
    case WM_LBUTTONDOWN:
        ptBeg.x = ptEnd.x = LOWORD(lParam);
        ptBeg.y = ptEnd.y = HIWORD(lParam);
        DrawBoxOutline(hwnd, ptBeg, ptEnd);
        
        SetCapture(hwnd);
        
        SetCursor(LoadCursor(NULL, IDC_CROSS));
        fBlocking = TRUE;
        return 0;
        
    case WM_MOUSEMOVE:
        if(fBlocking)
        {
            SetCursor(LoadCursor(NULL, IDC_CROSS));
            DrawBoxOutline(hwnd, ptBeg, ptEnd);
            ptEnd.x = LOWORD(lParam);
            ptEnd.y = HIWORD(lParam);
            DrawBoxOutline(hwnd, ptBeg, ptEnd);
        }
        return 0;
            
    case WM_LBUTTONUP:
        if(fBlocking)
        {
            DrawBoxOutline(hwnd, ptBeg, ptEnd);
            
            ptBoxBeg = ptBeg;
            ptBoxEnd.x = LOWORD(lParam);
            ptBoxEnd.y = HIWORD(lParam);
            
            ReleaseCapture();
            SetCursor(LoadCursor(NULL, IDC_ARROW));
            fBlocking = FALSE;
            fValidBox = TRUE;
            
            InvalidateRect(hwnd, NULL, TRUE);
        }
        return 0;
    
    case WM_CHAR:
        if(fBlocking & (wParam == '\x1B'))
        {
            DrawBoxOutline(hwnd, ptBeg, ptEnd);
            ReleaseCapture();
            SetCursor(LoadCursor(NULL, IDC_ARROW));
            fBlocking = FALSE;
        }
        return 0;
    
    case WM_PAINT:
        hdc = BeginPaint(hwnd, &ps);
        if(fValidBox)
        {
            SelectObject(hdc, GetStockObject(BLACK_BRUSH));
            Rectangle(hdc, ptBoxBeg.x, ptBoxBeg.y,
                ptBoxEnd.x, ptBoxEnd.y);
        }
        if(fBlocking)
        {
            SetROP2(hdc, R2_NOT);
            SelectObject(hdc, GetStockObject(NULL_BRUSH));
            Rectangle(hdc, ptBeg.x, ptBeg.y, ptEnd.x, ptEnd.y);
        }
        EndPaint(hwnd, &ps);
        return 0;
        
    case WM_DESTROY: 
        PostQuitMessage(0);
        return 0;            
    }
    return DefWindowProc(hwnd, message, wParam, lParam);
}