get screenshot

//
// Cteni screenshotu. Dynamicky vytvori handles, pokud je jeste nemame.
// Typy promennych - viz MSDN.
//
void get_screenshot()
{
  // vyrez obrazu, ktery chceme cist
  int x = image_x;   // offset
  int y = image_y;
  int cx = image_w;  // sirka, vyska od offsetu
  int cy = image_h;

  // Retrieve the handle to a display device context for the client area of the window.
  if (!hdcScreen) hdcScreen = GetDC(NULL);

  // Create a compatible DC which is used in a BitBlt from the window DC
  if (!hdcMemDC) hdcMemDC = CreateCompatibleDC(hdcScreen);

  if(!hdcMemDC)
  {
    printf("!hdcMemDC\n");
    return;
  }

  // Create a compatible bitmap from the Window DC
  if (!hbmScreen) hbmScreen = CreateCompatibleBitmap(hdcScreen, cx, cy);

  if(!hbmScreen)
  {
    printf("!hbmScreen\n");
    return;
  }

  // Select the compatible bitmap into the compatible memory DC.
  SelectObject(hdcMemDC,hbmScreen);

  // Bit block transfer into our compatible memory DC.
  if(!BitBlt(hdcMemDC,
    0,0,
    cx, cy,
    hdcScreen,
    x,y,
    SRCCOPY | CAPTUREBLT))
  {
    printf("BitBlt has failed\n");
    return;
  }

  // Get the BITMAP from the HBITMAP
  GetObject(hbmScreen,sizeof(BITMAP),&bmpScreen);

  // BITMAPFILEHEADER   bmfHeader;
  BITMAPINFOHEADER   bi;

  bi.biSize = sizeof(BITMAPINFOHEADER);
  bi.biWidth = bmpScreen.bmWidth;
  bi.biHeight = bmpScreen.bmHeight;
  bi.biPlanes = 1;
  bi.biBitCount = 32;
  bi.biCompression = BI_RGB;
  bi.biSizeImage = 0;
  bi.biXPelsPerMeter = 0;
  bi.biYPelsPerMeter = 0;
  bi.biClrUsed = 0;
  bi.biClrImportant = 0;

  DWORD dwBmpSize = ((bmpScreen.bmWidth * bi.biBitCount + 31) / 32) * 4 * bmpScreen.bmHeight;

  // alokace vnitrniho bufferu - ten pak vnitrne pouzivame
  if (!hDIB) hDIB = new unsigned char[dwBmpSize];

  // Zkopirovani do bufferu
  GetDIBits(hdcScreen, hbmScreen, 0,
    (UINT)bmpScreen.bmHeight,
    hDIB,//lpbitmap,
    (BITMAPINFO *)&bi, DIB_RGB_COLORS);
}