Capture all the GUI windows' Image that Running on the Desktop

#include <gdiplus.h>
using namespace Gdiplus;
GdiplusStartupInput gdiplusStartupInput;
ULONG_PTR gdiplusToken;
BOOL CvirtualDesktopDlg::OnInitDialog()
{
CDialogEx::OnInitDialog();

// Set the icon for this dialog. The framework does this automatically
// when the application‘s main window is not a dialog
SetIcon(m_hIcon, TRUE);    // Set big icon
SetIcon(m_hIcon, FALSE);    // Set small icon

// TODO: Add extra initialization here
GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);
std::ofstream mylog("mylog.log");
CWnd* pDesktopWnd = CWnd::GetDesktopWindow();
CWnd* pWnd = pDesktopWnd->GetWindow(GW_CHILD);
int jpgnum = 0;
while (pWnd != NULL)
{
mylog << "number:" << jpgnum << endl;
CString strClassName = _T(" ");
::GetClassName(pWnd->GetSafeHwnd(), strClassName.GetBuffer(256), 256);
mylog << "class name\t:" << (CT2A)(LPCTSTR) strClassName << endl;
CString strWindowText = _T(" ");
::GetWindowText(pWnd->GetSafeHwnd(), strWindowText.GetBuffer(256), 256);
mylog << "window text\t:" << (CT2A)(LPCTSTR)strWindowText << endl;

char jpgfilename[1024];
sprintf_s(jpgfilename, "jpg_%d.jpg", jpgnum++);
//jpgfilename.Format(_T("jpg_%d"), jpgnum++);
USES_CONVERSION;
saveDesktoptoJPG(A2T(jpgfilename), pWnd->m_hWnd);

pWnd = pWnd->GetWindow(GW_HWNDNEXT);
}
mylog.close();
return TRUE; // return TRUE unless you set the focus to a control
}

void CvirtualDesktopDlg::saveDesktoptoJPG(TCHAR *jpgFilePathName, HWND hwnd)
{
//Get desktop DC
/*
HWND hDeskWnd = ::GetDesktopWindow();
CDC *pDestDC = CDC::FromHandle(::GetDC(hDeskWnd));
*/
CDC *pDestDC = CDC::FromHandle(::GetDC(hwnd) );
int screenWidth = pDestDC->GetDeviceCaps(HORZRES);
int screenHeight = pDestDC->GetDeviceCaps(VERTRES);
//Create Bitmap that is comatible with desktop
CBitmap memBitmap;
memBitmap.CreateCompatibleBitmap(pDestDC, screenWidth, screenHeight);
//create memory DC for desktop
CDC memDC;
memDC.CreateCompatibleDC(pDestDC);
memDC.SelectObject(&memBitmap);
//copy desktop DC to the memery DC
memDC.BitBlt(0, 0, screenWidth, screenHeight, pDestDC, 0, 0, SRCCOPY);
//obtain the bitmap information
BITMAP bmpInfo;
memBitmap.GetBitmap(&bmpInfo);
//generate BITMAPINFO
BITMAPINFO m_BITMAPINFO;
memset(&m_BITMAPINFO, 0, sizeof(BITMAPINFO));
m_BITMAPINFO.bmiHeader.biSize = sizeof(BITMAPINFO);
m_BITMAPINFO.bmiHeader.biPlanes = 1;
m_BITMAPINFO.bmiHeader.biBitCount = bmpInfo.bmBitsPixel;
m_BITMAPINFO.bmiHeader.biCompression = BI_RGB;
m_BITMAPINFO.bmiHeader.biWidth = bmpInfo.bmWidth;
m_BITMAPINFO.bmiHeader.biHeight = bmpInfo.bmHeight;
//get the data of bitmap
BYTE* pBuffer = new BYTE[bmpInfo.bmWidthBytes*bmpInfo.bmHeight];
GetDIBits(memDC.m_hDC, (HBITMAP)memBitmap.m_hObject, 0, screenHeight, pBuffer, (LPBITMAPINFO)&m_BITMAPINFO, DIB_RGB_COLORS);
//generate bitmap
Bitmap *pSrcBmp = Bitmap::FromBITMAPINFO(&m_BITMAPINFO, (void*)pBuffer);
//save to jpg
CLSID encoderClsid;
GetEncoderClsid(L"image/jpeg", &encoderClsid);
// pSrcBmp->Save(L"D:\\desktop.jpg", &encoderClsid);
pSrcBmp->Save(jpgFilePathName, &encoderClsid);

delete pSrcBmp;
delete pBuffer;
ReleaseDC(pDestDC);
}
int CvirtualDesktopDlg::GetEncoderClsid(const WCHAR* format, CLSID* pClsid)
{
/*
The preceding code produces the following output:
image/bmp
image/jpeg
image/gif
image/x-emf
image/x-wmf
image/tiff
image/png
image/x-icon
*/
UINT num = 0; // number of image decoders
UINT size = 0; // size, in bytes, of the image decoder array

ImageCodecInfo* pImageCodecInfo = NULL;
// How many decoders are there?
// How big (in bytes) is the array of all ImageCodecInfo objects?
GetImageEncodersSize(&num, &size);
if (size == 0)
{
return -1;
}
// Create a buffer large enough to hold the array of ImageCodecInfo
// objects that will be returned by GetImageDecoders.
pImageCodecInfo = (ImageCodecInfo*)(malloc(size));
if (pImageCodecInfo == NULL)
{
return -1;
}
// GetImageDecoders creates an array of ImageCodecInfo objects
// and copies that array into a previously allocated buffer.
// The third argument, imageCodecInfos, is a pointer to that buffer.
GetImageEncoders(num, size, pImageCodecInfo);

for (UINT j = 0; j< num; ++j)
{
if (wcscmp(pImageCodecInfo[j].MimeType, format) == 0)
{
*pClsid = pImageCodecInfo[j].Clsid;
free(pImageCodecInfo);
return j; //success
}
}
free(pImageCodecInfo);
return -1; //failure
}