c++ - Does GDI+ have standard image encoder CLSIDs?

Question

The GDI+ Image::Save method requires a CLSID parameter to specify the encoder to use. The documentation points to some sample code for getting the encoder associated with a particular MIME type, such as image/jpeg or image/png. However I'm balking at the thought of copying a half-page function just to support a 1-line debugging aid where I save an intermediate result out to disk.

Shouldn't there be a list of standard CLSIDs for the standard encoders? Where would I find such a list? I haven't been able to find one by searching Microsoft's include files.

Answer 1

There isn't one. I think they intended the codec list to be extensible and support plugins, but never got around to it. Given that they haven't made any changes to GDI+ in quite some time, they likely won't anytime soon. You could probably get away with generating your own hard coded list based on an enumeration of Gdiplus::GetImageEncoders.

That is:

image/bmp  : {557cf400-1a04-11d3-9a73-0000f81ef32e}
image/jpeg : {557cf401-1a04-11d3-9a73-0000f81ef32e} 
image/gif  : {557cf402-1a04-11d3-9a73-0000f81ef32e} 
image/tiff : {557cf405-1a04-11d3-9a73-0000f81ef32e}
image/png  : {557cf406-1a04-11d3-9a73-0000f81ef32e}

Here's the function I routinely cut&paste between projects for getting at the CLSID of the encoder. You could modify it to be a table lookup.

#include <windows.h>
#include <gdiplus.h>
#include <string>
#include <vector>

HRESULT GetGdiplusEncoderClsid(const std::wstring& format, GUID* pGuid)
{
    HRESULT hr = S_OK;
    UINT  nEncoders = 0;          // number of image encoders
    UINT  nSize = 0;              // size of the image encoder array in bytes
    std::vector<BYTE> spData;
    Gdiplus::ImageCodecInfo* pImageCodecInfo = NULL;
    Gdiplus::Status status;
    bool found = false;

    if (format.empty() || !pGuid)
    {
        hr = E_INVALIDARG;
    }

    if (SUCCEEDED(hr))
    {
        *pGuid = GUID_NULL;
        status = Gdiplus::GetImageEncodersSize(&nEncoders, &nSize);

        if ((status != Gdiplus::Ok) || (nSize == 0))
        {
            hr = E_FAIL;
        }
    }

    if (SUCCEEDED(hr))
    {

        spData.resize(nSize);
        pImageCodecInfo = (Gdiplus::ImageCodecInfo*)&spData.front();
        status = Gdiplus::GetImageEncoders(nEncoders, nSize, pImageCodecInfo);

        if (status != Gdiplus::Ok)
        {
            hr = E_FAIL;
        }
    }

    if (SUCCEEDED(hr))
    {
        for (UINT j = 0; j < nEncoders && !found; j++)
        {
            if (pImageCodecInfo[j].MimeType == format)
            {
                *pGuid = pImageCodecInfo[j].Clsid;
                found = true;
            }
        }

        hr = found ? S_OK : E_FAIL;
    }

    return hr;
}


int main()
{
    Gdiplus::GdiplusStartupInput gdiplusStartupInput;
    ULONG_PTR gdiplusToken;
    GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);

    GUID guidBmp = {};
    GUID guidJpeg = {};
    GUID guidGif = {};
    GUID guidTiff = {};
    GUID guidPng = {};

    GetGdiplusEncoderClsid(L"image/bmp", &guidBmp);
    GetGdiplusEncoderClsid(L"image/jpeg", &guidJpeg);
    GetGdiplusEncoderClsid(L"image/gif", &guidGif);
    GetGdiplusEncoderClsid(L"image/tiff", &guidTiff);
    GetGdiplusEncoderClsid(L"image/png", &guidPng);

    return 0;
}