C++ Programming: Easy Screen Capture Using MFC/ATL

Introduction

CImage is a class shared by MFC and ATL. It provides support for easy manipulation of bitmaps and different graphic file formats (BMP, JPEG, GIF, and PNG). This article presents an extension class having methods for screen images capture.

CScreenImage class

CScreenImage is derived from CImage, uses shared MFC/ATL classes and plain Windows API, so can be inserted in any MFC or ATL-based application.

class CScreenImage : public CImage
{
public:
    BOOL CaptureRect(const CRect& rect) throw();
    BOOL CaptureScreen() throw();
    BOOL CaptureWindow(HWND hWnd) throw();
};

• CScreenImage::CaptureRect - captures an image from a given screen area;
• CScreenImage::CaptureScreen - captures the entire screen image of the first monitor;
• CScreenImage::CaptureWindow - captures the image of a given window.

/********************************************************************
 Function:   CScreenImage::CaptureRect
 Purpose:    captures a screen rectangle
 Parameters: rect: screen rectangle to be captured
 Return:     non-zero value if successful
*********************************************************************/
BOOL CScreenImage::CaptureRect(const CRect& rect)
{
   // detach and destroy the old bitmap if any attached
   CImage::Destroy();
   
   // create a screen and a memory device context
   HDC hDCScreen = ::CreateDC(_T("DISPLAY"), NULL, NULL, NULL);
   HDC hDCMem = ::CreateCompatibleDC(hDCScreen);
   // create a compatible bitmap and select it in the memory DC
   HBITMAP hBitmap = 
      ::CreateCompatibleBitmap(hDCScreen, rect.Width(), rect.Height());
   HBITMAP hBmpOld = (HBITMAP)::SelectObject(hDCMem, hBitmap);

   // bit-blit from screen to memory device context
   // note: CAPTUREBLT flag is required to capture layered windows
   DWORD dwRop = SRCCOPY | CAPTUREBLT;
   BOOL bRet = ::BitBlt(hDCMem, 0, 0, rect.Width(), rect.Height(), 
                        hDCScreen, rect.left, rect.top, dwRop);
   // attach bitmap handle to this object
   Attach(hBitmap);

   // restore the memory DC and perform cleanup
   ::SelectObject(hDCMem, hBmpOld);
   ::DeleteDC(hDCMem);
   ::DeleteDC(hDCScreen);

   return bRet;
}

Demo application

The demo application is a simple SDI application which uses CScreenImage class to capture images from the screen and display them in a view.

From the Capture menu you can choose the following items:

• Screen, to capture the entire screen image of the first monitor;
• Foreground window, to capture the image of the window with which the user is currently working;
• Rectangle, to capture the image of a selected screen area, using the mouse.

Related links

• [MSDN] Capturing an Image
• [MSDN] CImage Class
• [Codeguru FAQ] How to capture layered windows?