Taking a JPEG-encoded screenshot to a buffer using GDI+ and C++

Question

I\'ve adapted this code from another article here on SO. It takes a screenshot of the desktop and writes it to a file named \"test.jpg.\"

I\'m interested in saving t

Answer 1

Short answer: Use the IStream version of Gdiplus::Image::Save. Use CreateHStreamOnGlobal to make a temporary IStream that you can convert back to a buffer;

Long winded version with code sample.

Replace this line:

 iRes = (pScreenShot->Save(lpszFilename, &imageCLSID, &encoderParams) == Ok);

With this block of code:

// Note: For the sake of brevity and readability, I'm deliberately not checking
// the return value of any of these calls. In production code, you should do diligent error 
// checking on each function call. Also, there may be an optimization where you can just
// use the memory of the stream itself (by calling GetHGlobalFromStream and GlobalLock)
// But that's an exercise left to the reader.

{
    IStream *pStream = NULL;
    LARGE_INTEGER liZero = {};
    ULARGE_INTEGER pos = {};
    STATSTG stg = {};
    ULONG bytesRead=0;
    HRESULT hrRet=S_OK;

    BYTE* buffer = NULL;  // this is your buffer that will hold the jpeg bytes
    DWORD dwBufferSize = 0;  // this is the size of that buffer;


    hrRet = CreateStreamOnHGlobal(NULL, TRUE, &pStream))
    hrRet = pScreenShot->Save(pStream, &imageCLSID, &encoderParams) == 0 ? S_OK : E_FAIL;
    hrRet = pStream->Seek(liZero, STREAM_SEEK_SET, &pos);
    hrRet = pStream->Stat(&stg, STATFLAG_NONAME);

    // allocate a byte buffer big enough to hold the jpeg stream in memory
    buffer = new BYTE[stg.cbSize.LowPart];
    hrRet = (buffer == NULL) ? E_OUTOFMEMORY : S_OK;
    dwBufferSize = stg.cbSize.LowPart;

    // copy the stream into memory
    hrRet = pStream->Read(buffer, stg.cbSize.LowPart, &bytesRead);

    // now go save "buffer" and "dwBufferSize" off somewhere.  This is the jpeg buffer
    // don't forget to free it when you are done

    // After success or if any of the above calls fail, don't forget to release the stream
    if (pStream)
    {
        pStream->Release();
    }
}