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

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;
}

Answer 2

If you just want to write a PNG, this appears to work:
// image/png : {557cf406-1a04-11d3-9a73-0000f81ef32e}
const CLSID pngEncoderClsId = { 0x557cf406, 0x1a04, 0x11d3,{ 0x9a,0x73,0x00,0x00,0xf8,0x1e,0xf3,0x2e } };
stat = image->Save(L"test.png", &pngEncoderClsId, NULL);
Note the reformatting of the hex values.
From:
How to initialize a constant CLSID

Answer 3

You will probably want to use ImageCodecInfo with GetImageEncodersSize() and GetImageEncoders() I'm not aware of any easier way.
EDIT: If you know specifically what you want and damn all the rest you can get away with doing something like this ...
CLSID pngClsid;
GetEncoderClsid("image/png", &pngClsid);
image.Save("imagename.png", &pngClsid, NULL);