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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; 
    }


 

 

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