SetCapture

    技术2022-05-12  2

    BLOKOUT2.C     /*----------------------------------------------------------------------------           BLOKOUT2.C   --   Mouse   Button   &   Capture   Demo   Program     (c)   Charles   Petzold,   1998     ----------------------------------------------------------------------------*/          #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   ("BlokOut2")   ;               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   ("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')               //   i.e.,   Escape                          {                                   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)   ;     }     摘自《Windows   Programming》

        一般,只有鼠标在CWnd的客户区内,你才能接受到鼠标消息。调用SetCapture后,即使鼠标移动出客户区,你也可以接受到鼠标消息。不过系统中只能有一个程序调用SetCapture,所以你需要在不使用时调用ReleaseCapture释放。而GetCapture可以知道当前哪个窗口调用了SetCapture。


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