How to write an image to STDOUT with Wincodec.h (WIC)

Question

I came across this example and couldn't figure out how to change stream->InitializeFromFilename to something that outputs to STDOUT, inside the HRESULT SavePixelsToFile32bppPBGRA(UINT width, UINT height, UINT stride, LPBYTE pixels, LPWSTR filePath, const GUID &format) function. Tried using stream->InitializeFromMemory but hit a wall due to minimal C++ experience.

Reasons behind this is that i'm building something and would like to pipe the stdout of the example using something else.

Answer 1

Thanks to @SimonMourier, I was able to update his code to achieve what was needed.

SavePixelsToFile32bppPBGRA now writes the data to an IStream pointer, streamOut. It also invokes a new function at the end, to output data.

HRESULT SavePixelsToFile32bppPBGRA(UINT width, UINT height, UINT stride, LPBYTE pixels, const GUID& format)
{
    if (!pixels)
        return E_INVALIDARG;

    HRESULT hr = S_OK;
    IWICImagingFactory* factory = nullptr;
    IWICBitmapEncoder* encoder = nullptr;
    IWICBitmapFrameEncode* frame = nullptr;
    IWICStream* streamOut = nullptr;
    IStream * streamIn = nullptr;
    GUID pf = GUID_WICPixelFormat32bppPBGRA;
    BOOL coInit = CoInitialize(nullptr);

    HRCHECK(CoCreateInstance(CLSID_WICImagingFactory, nullptr, CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&factory)));
    HRCHECK(factory->CreateStream(&streamOut));
    HRCHECK(CreateStreamOnHGlobal(NULL, true, &streamIn));
    HRCHECK(streamOut->InitializeFromIStream(streamIn));
    HRCHECK(factory->CreateEncoder(format, nullptr, &encoder));
    HRCHECK(encoder->Initialize(streamOut, WICBitmapEncoderNoCache));
    HRCHECK(encoder->CreateNewFrame(&frame, nullptr)); // we don't use options here
    HRCHECK(frame->Initialize(nullptr)); // we dont' use any options here
    HRCHECK(frame->SetSize(width, height));
    HRCHECK(frame->SetPixelFormat(&pf));
    HRCHECK(frame->WritePixels(height, stride, stride * height, pixels));
    HRCHECK(frame->Commit());
    HRCHECK(encoder->Commit());

    sendIStreamToOutput(streamOut);

cleanup:
    RELEASE(streamIn);
    RELEASE(streamOut);
    RELEASE(frame);
    RELEASE(encoder);
    RELEASE(factory);
    if (coInit) CoUninitialize();
    return hr;
}

sendIStreamToOutput reads the data from the IStream and writes it to std::cout (with binary mode active).

void sendIStreamToOutput (IStream * pIStream) {

    STATSTG sts;
    pIStream->Stat(&sts, STATFLAG_DEFAULT);
    ULARGE_INTEGER uli = sts.cbSize;
    LARGE_INTEGER zero;
    zero.QuadPart = 0;
    ULONG size = (ULONG)uli.QuadPart;
    char* bits = new char[size];
    ULONG written;
    pIStream->Seek(zero, STREAM_SEEK_SET, NULL);
    pIStream->Read(bits, size, &written);
    
    std::ostream& lhs = std::cout;

    _setmode(_fileno(stdout), _O_BINARY);

    lhs.write(bits, size);

    fflush(stdout);

    delete[] bits;
 }