C / C++ / MFC

-- Moby, We are all made of stars

1. In an SDI app, I defined the following global variable in the view class:
   

   CDC* g_pMemoryDC = NULL;

   
   
2. In a menu handler for screen capture I added the following code. Note that the hiding of the window and sleeping are done just to get the app out of the way so that I can capture the desktop without my app.
   

   if (g_pMemoryDC)
   {
     delete g_pMemoryDC;
     g_pMemoryDC = NULL;
   }
   g_pMemoryDC = new CDC();
   
   GetParentFrame()->ShowWindow(SW_HIDE);
   Sleep(1000);
   
   CDC screenDC;
   screenDC.CreateDC("DISPLAY", NULL, NULL, NULL);
   int nHeight = screenDC.GetDeviceCaps(HORZRES);
   int nWidth = screenDC.GetDeviceCaps(VERTRES);
   
   CBitmap bitmap;
   g_pMemoryDC->CreateCompatibleDC(&screenDC);
   bitmap.CreateCompatibleBitmap(&screenDC, nWidth, nHeight);
   g_pMemoryDC->SelectObject(&bitmap);
   g_pMemoryDC->BitBlt(0, 0, nWidth, nHeight, &screenDC, 0, 0, SRCCOPY);
   
   GetParentFrame()->ShowWindow(SW_SHOW);
   
   Invalidate();
   

   
   
3. In the OnDraw, I add the following.
   

   if (g_pMemoryDC)
   {
     CClientDC clientDC(this);
     int nWidth = g_pMemoryDC->GetDeviceCaps(HORZRES);
     int nHeight = g_pMemoryDC->GetDeviceCaps(VERTRES);
   
     clientDC.BitBlt(0, 0, nWidth, nHeight, g_pMemoryDC, 0, 0, SRCCOPY);
   }