SetCapture

 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。

1. BLOKOUT2.C   
2.   /*----------------------------------------------------------------------------   
3.         BLOKOUT2.C   --   Mouse   Button   &   Capture   Demo   Program   
4.   (c)   Charles   Petzold,   1998   
5.   ----------------------------------------------------------------------------*/   
6.     
7.   #include   <windows.h>   
8.   LRESULT   CALLBACK   WndProc   (HWND,   UINT,   WPARAM,   LPARAM)   ;   
9.   int   WINAPI   WinMain   (HINSTANCE   hInstance,   HINSTANCE   hPrevInstance,   
10.   PSTR   szCmdLine,   int   iCmdShow)   
11.   {   
12.             static   TCHAR   szAppName[]   =   TEXT   ("BlokOut2")   ;   
13.             HWND                   hwnd   ;   
14.             MSG                     msg   ;   
15.             WNDCLASS           wndclass   ;   
16.     
17.           wndclass.style     =   CS_HREDRAW   |   CS_VREDRAW   ;   
18.             wndclass.lpfnWndProc       =   WndProc   ;   
19.             wndclass.cbClsExtra         =   0   ;   
20.             wndclass.cbWndExtra         =   0   ;   
21.             wndclass.hInstance           =   hInstance   ;   
22.             wndclass.hIcon                   =   LoadIcon   (NULL,   IDI_APPLICATION)   ;   
23.     wndclass.hCursor               =   LoadCursor   (NULL,   IDC_ARROW)   ;   
24.             wndclass.hbrBackground   =   (HBRUSH)   GetStockObject   (WHITE_BRUSH)   ;   
25.             wndclass.lpszMenuName     =   NULL   ;   
26.             wndclass.lpszClassName   =   szAppName   ;   
27.               
28.   if   (!RegisterClass   (&wndclass))   
29.             {   
30.       MessageBox   ( NULL,   TEXT   ("Program   requires   Windows   NT!"),     
31.   szAppName,   MB_ICONERROR)   ;   
32.   return   0   ;   
33.     }   
34.     
35.             hwnd   =   CreateWindow   ( szAppName,   TEXT   ("Mouse   Button   &   Capture   Demo"),   
36.   WS_OVERLAPPEDWINDOW,   
37.                                           CW_USEDEFAULT,   CW_USEDEFAULT,   
38.                                           CW_USEDEFAULT,   CW_USEDEFAULT,   
39.                                           NULL,   NULL,   hInstance,   NULL)   ;   
40.               
41.             ShowWindow   (hwnd,   iCmdShow)   ;   
42.             UpdateWindow   (hwnd)   ;   
43.               
44.             while   (GetMessage   (&msg,   NULL,   0,   0))   
45.             {   
46.                       TranslateMessage   (&msg)   ;   
47.                       DispatchMessage   (&msg)   ;   
48.             }   
49.             return   msg.wParam   ;   
50.   }   
51.     
52.   void   DrawBoxOutline   (HWND   hwnd,   POINT   ptBeg,   POINT   ptEnd)   
53.   {   
54.             HDC   hdc   ;   
55.             hdc   =   GetDC   (hwnd)   ;   
56.             SetROP2   (hdc,   R2_NOT)   ;   
57.             SelectObject   (hdc,   GetStockObject   (NULL_BRUSH))   ;   
58.             Rectangle   (hdc,   ptBeg.x,   ptBeg.y,   ptEnd.x,   ptEnd.y)   ;   
59.               
60.             ReleaseDC   (hwnd,   hdc)   ;   
61.   }   
62.     
63.   LRESULT   CALLBACK   WndProc   ( HWND   hwnd,   UINT   message,   WPARAM   wParam,LPARAM   lParam)   
64.   {   
65.             static   BOOL     fBlocking,   fValidBox   ;   
66.             static   POINT   ptBeg,   ptEnd,   ptBoxBeg,   ptBoxEnd   ;   
67.             HDC                     hdc   ;   
68.             PAINTSTRUCT     ps   ;   
69.               
70.             switch   (message)   
71.             {   
72.             case   WM_LBUTTONDOWN   :   
73.                       ptBeg.x   =   ptEnd.x   =   LOWORD   (lParam)   ;   
74.                       ptBeg.y   =   ptEnd.y   =   HIWORD   (lParam)   ;   
75.                         
76.                       DrawBoxOutline   (hwnd,   ptBeg,   ptEnd)   ;   
77.     
78.                       SetCapture   (hwnd)   ;   
79.                       SetCursor   (LoadCursor   (NULL,   IDC_CROSS))   ;   
80.                         
81.                       fBlocking   =   TRUE   ;   
82.                       return   0   ;   
83.                         
84.             case   WM_MOUSEMOVE   :   
85.                       if   (fBlocking)   
86.                       {   
87.                                 SetCursor   (LoadCursor   (NULL,   IDC_CROSS))   ;   
88.                                   
89.                                 DrawBoxOutline   (hwnd,   ptBeg,   ptEnd)   ;   
90.                                   
91.                                 ptEnd.x   =   LOWORD   (lParam)   ;   
92.                                 ptEnd.y   =   HIWORD   (lParam)   ;   
93.                                   
94.                                 DrawBoxOutline   (hwnd,   ptBeg,   ptEnd)   ;   
95.                       }   
96.                   return   0   ;   
97.                         
98.             case   WM_LBUTTONUP   :   
99.                       if   (fBlocking)   
100.                       {   
101.                                 DrawBoxOutline   (hwnd,   ptBeg,   ptEnd)   ;   
102.                                   
103.                                 ptBoxBeg       =   ptBeg   ;   
104.                                 ptBoxEnd.x   =   LOWORD   (lParam)   ;   
105.                                 ptBoxEnd.y   =   HIWORD   (lParam)   ;   
106.                                   
107.                                 ReleaseCapture   ()   ;   
108.                                 SetCursor   (LoadCursor   (NULL,   IDC_ARROW))   ;   
109.                                   
110.                                 fBlocking   =   FALSE   ;   
111.                                 fValidBox     =   TRUE   ;   
112.                                   
113.                                 InvalidateRect   (hwnd,   NULL,   TRUE)   ;   
114.                       }   
115.                       return   0   ;   
116.                         
117.             case   WM_CHAR   :   
118.                       if   (fBlocking   &   wParam   ==   '/x1B')               //   i.e.,   Escape   
119.                       {   
120.                                 DrawBoxOutline   (hwnd,   ptBeg,   ptEnd)   ;   
121.                                 ReleaseCapture   ()   ;   
122.                                 SetCursor   (LoadCursor   (NULL,   IDC_ARROW))   ;   
123.     
124.                                 fBlocking   =   FALSE   ;   
125.                       }   
126.                       return   0   ;   
127.                         
128.             case   WM_PAINT   :   
129.                       hdc   =   BeginPaint   (hwnd,   &ps)   ;   
130.                         
131.                       if   (fValidBox)   
132.                       {   
133.                                 SelectObject   (hdc,   GetStockObject   (BLACK_BRUSH))   ;   
134.                                 Rectangle   (hdc,   ptBoxBeg.x,   ptBoxBeg.y,   
135.                                           ptBoxEnd.x,   ptBoxEnd.y)   ;   
136.                       }   
137.                         
138.                       if   (fBlocking)   
139.                       {   
140.                                 SetROP2   (hdc,   R2_NOT)   ;   
141.                                 SelectObject   (hdc,   GetStockObject   (NULL_BRUSH))   ;   
142.                                 Rectangle   (hdc,   ptBeg.x,   ptBeg.y,   ptEnd.x,   ptEnd.y)   ;   
143.                       }   
144.                         
145.                       EndPaint   (hwnd,   &ps)   ;   
146.                       return   0   ;   
147.                         
148.             case   WM_DESTROY   :   
149.                       PostQuitMessage   (0)   ;   
150.                       return   0   ;   
151.             }   
152.             return   DefWindowProc   (hwnd,   message,   wParam,   lParam)   ;   
153.   }   
154.   摘自《Windows   Programming》