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。
