C / C++ / MFC

STDMETHODIMP CCaptureWindow::SaveScreenshot(LPTSTR pFile)
{
  if (!g_pCapture || !g_pBaseFilter)
	return E_UNEXPECTED;

  CComPtr<IDDrawExclModeVideo> ddemv;
  HRESULT hr;
  if (FAILED(g_pCapture->FindInterface(&PIN_CATEGORY_PREVIEW,
	&MEDIATYPE_Interleaved, g_pBaseFilter,
	IID_IDDrawExclModeVideo, (void**)&ddemv)))
  {
	if (FAILED(hr = g_pCapture->FindInterface(&PIN_CATEGORY_PREVIEW,
	  &MEDIATYPE_Video, g_pBaseFilter,
	  IID_IDDrawExclModeVideo, (void**)&ddemv)))
	{
	  return hr;
	}
  }
  // ok take the screenshot now
  CComPtr<IDirectDrawSurface> pSurface;
  CComPtr<IDirectDrawSurface7> pSurface7;
  BOOL bExternal;
  if (FAILED(hr=ddemv->GetDDrawSurface(&pSurface,&bExternal)))
	return hr;

  if (FAILED(hr=pSurface->QueryInterface(IID_IDirectDrawSurface7,(void**)&pSurface7)))
	return hr;

  
  DDSURFACEDESC2 desc;
  desc.dwSize = sizeof(desc);
  if (FAILED(hr=pSurface7->Lock(NULL,&desc,DDLOCK_WAIT | DDLOCK_READONLY,0)))
	return hr;

  // now make sure we can save it to a file
  if ((desc.ddpfPixelFormat.dwRGBBitCount < 24) || !(desc.ddpfPixelFormat.dwFlags & DDPF_RGB) || (desc.ddpfPixelFormat.dwFlags & DDPF_PALETTEINDEXEDTO8))
  {
	pSurface7->Unlock(NULL);
	return E_UNEXPECTED;
  }

  // now create the file
  HANDLE hFile = CreateFile(pFile,GENERIC_WRITE,0,NULL,CREATE_ALWAYS,FILE_ATTRIBUTE_NORMAL,0);
  if (hFile == INVALID_HANDLE_VALUE)
  {
	pSurface7->Unlock(NULL);
	return GetLastError();
  }

  CFile file(hFile);
  BITMAPFILEHEADER bfh;
  BITMAPINFO bmi;
  DWORD sizeImage;

  // fill in common areas
  bfh.bfType = MAKEWORD('B','M');
  bfh.bfReserved1 = 0;
  bfh.bfReserved2 = 0;
  bfh.bfOffBits = sizeof(bmi.bmiHeader);
  bmi.bmiHeader.biSize = sizeof(bmi.bmiHeader);
  bmi.bmiHeader.biPlanes = 1;
  bmi.bmiHeader.biCompression = BI_RGB;
  bmi.bmiHeader.biXPelsPerMeter = 0;
  bmi.bmiHeader.biYPelsPerMeter = 0;
  bmi.bmiHeader.biClrUsed = 0;
  bmi.bmiHeader.biClrImportant = 0;
  bmi.bmiHeader.biWidth = desc.dwWidth;
  bmi.bmiHeader.biHeight = desc.dwHeight;

  /* this leaves only
  
	bfh.bfSize = sizeof(bfh) + sizeof(bmi.bmiHeader) + sizeImage;
	bmi.bmiHeader.biBitCount = ;
	bmi.bmiHeader.biSizeImage = sizeImage;

	*/
  if (desc.ddpfPixelFormat.dwRGBBitCount == 32)
  {
	// must do 32 bit case - downsample to 24 bit
	DWORD lPitch = desc.dwWidth * 3;
	// round it to a DWORD boundary
	if (lPitch & 3)
	  lPitch = (lPitch & ~3) + 4;

	// allocate memory for it
	sizeImage = desc.dwHeight * lPitch;
	LPBYTE pBitmapMem = (LPBYTE)CoTaskMemAlloc(sizeImage+4);
	if (!pBitmapMem)
	{
	  pSurface7->Unlock(NULL);
	  return E_OUTOFMEMORY;
	}  	
	
	// now do the conversion here
	LPBYTE pCurrentWriteMem = (LPBYTE)pBitmapMem;
	LPBYTE pCurrentReadMem = (LPBYTE)((LPBYTE)desc.lpSurface+((desc.dwHeight-1)*desc.lPitch));
	for (DWORD i=0;i<desc.dwHeight;++i)
	{
	  // current line pointer
	  LPBYTE curWLine = pCurrentWriteMem;
	  LPBYTE curRLine = pCurrentReadMem;
	  // now copy the entire line over
	  for (DWORD j=0;j<desc.dwWidth;++j)
	  {
		// RGB 
		// BGR
		pCurrentWriteMem[0] = pCurrentReadMem[0];
		pCurrentWriteMem[1] = pCurrentReadMem[1];
		pCurrentWriteMem[2] = pCurrentReadMem[2];
		
		pCurrentWriteMem += 3;
		pCurrentReadMem  += 4;
	  }
	  // update where lines point
	  pCurrentWriteMem = curWLine + lPitch;
	  pCurrentReadMem  = curRLine - desc.lPitch;
	}
	// update headers
	bfh.bfSize = sizeof(bfh) + sizeof(bmi.bmiHeader) + sizeImage;
	bmi.bmiHeader.biBitCount = 24;
	bmi.bmiHeader.biSizeImage = sizeImage;

	// write the stuff now
	file.Write(&bfh,sizeof(bfh));
	file.Write(&bmi,sizeof(bmi.bmiHeader));
	file.Write(pBitmapMem,sizeImage);

	CoTaskMemFree(pBitmapMem);
  }
  else
  {	
	sizeImage = desc.dwHeight * desc.lPitch;
	
	bfh.bfSize = sizeof(bfh) + sizeof(bmi.bmiHeader) + sizeImage;
	bmi.bmiHeader.biBitCount = (WORD)desc.ddpfPixelFormat.dwRGBBitCount;
	bmi.bmiHeader.biSizeImage = sizeImage;
	
	// write the stuff now
	file.Write(&bfh,sizeof(bfh));
	file.Write(&bmi,sizeof(bmi.bmiHeader));
	file.Write(desc.lpSurface,sizeImage);
  }
  
  file.Close();
  pSurface7->Unlock(NULL);
  return S_OK;
}