Clipping Output

After the user clicks Clip from the menu, the application uses the coordinates of the rectangle the user created to define a clipping region. After defining the clipping region and selecting it into the application's device context, the application redraws the bitmapped image. The application performs these tasks, as follows.

// These variables are required for clipping. 
 
static POINT ptUpperLeft; 
static POINT ptLowerRight; 
static POINT aptRect[5]; 
static POINT ptTmp; 
static POINTS ptsTmp; 
static BOOL fDefineRegion; 
static BOOL fRegionExists; 
static HRGN hrgn; 
static RECT rctTmp; 
int i; 
 
case WM_COMMAND: 
 switch (wParam) 
 { 
 
 case IDM_CLIP: 
 
 hdc = GetDC(hwnd); 
 
 // Retrieve the application's client rectangle and paint 
 // with the default (white) brush. 
 
 GetClientRect(hwnd, &rctTmp); 
 FillRect(hdc, &rctTmp, GetStockObject(WHITE_BRUSH)); 
 
 // Use the rect coordinates to define a clipping region. 
 
 hrgn = CreateRectRgn(aptRect[0].x, aptRect[0].y, 
 aptRect[2].x, aptRect[2].y); 
 SelectClipRgn(hdc, hrgn); 
 
 // Transfer (draw) the bitmap into the clipped rectangle. 
 
 BitBlt(hdc, 
 0, 0, 
 bmp.bmWidth, bmp.bmHeight, 
 hdcCompatible, 
 0, 0, 
 SRCCOPY); 
 
 ReleaseDC(hwnd, hdc); 
 break; 
 }