Retrieving the Class Identifier for an Encoder
The function GetEncoderClsid in the following example receives the MIME type of an encoder and returns the class identifier (CLSID) of that encoder. The MIME types of the encoders built into Windows GDI+ are as follows:
- image/bmp
- image/jpeg
- image/gif
- image/tiff
- image/png
The function calls GetImageEncoders to get an array of ImageCodecInfo objects. If one of the ImageCodecInfo objects in that array represents the requested encoder, the function returns the index of the ImageCodecInfo object and copies the CLSID into the variable pointed to by pClsid. If the function fails, it returns –1.
int GetEncoderClsid(const WCHAR* format, CLSID* pClsid)
{
UINT num = 0; // number of image encoders
UINT size = 0; // size of the image encoder array in bytes
ImageCodecInfo* pImageCodecInfo = NULL;
GetImageEncodersSize(&num, &size);
if(size == 0)
return -1; // Failure
pImageCodecInfo = (ImageCodecInfo*)(malloc(size));
if(pImageCodecInfo == NULL)
return -1; // Failure
GetImageEncoders(num, size, pImageCodecInfo);
for(UINT j = 0; j < num; ++j)
{
if( wcscmp(pImageCodecInfo[j].MimeType, format) == 0 )
{
*pClsid = pImageCodecInfo[j].Clsid;
free(pImageCodecInfo);
return j; // Success
}
}
free(pImageCodecInfo);
return -1; // Failure
}
The following console application calls the GetEncoderClsid function to determine the CLSID of the PNG encoder:
#include <windows.h>
#include <gdiplus.h>
#include <stdio.h>
using namespace Gdiplus;
#include "GdiplusHelperFunctions.h"
INT main()
{
// Initialize GDI+.
GdiplusStartupInput gdiplusStartupInput;
ULONG_PTR gdiplusToken;
GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);
CLSID encoderClsid;
INT result;
WCHAR strGuid[39];
result = GetEncoderClsid(L"image/png", &encoderClsid);
if(result < 0)
{
printf("The PNG encoder is not installed.\n");
}
else
{
StringFromGUID2(encoderClsid, strGuid, 39);
printf("An ImageCodecInfo object representing the PNG encoder\n");
printf("was found at position %d in the array.\n", result);
wprintf(L"The CLSID of the PNG encoder is %s.\n", strGuid);
}
GdiplusShutdown(gdiplusToken);
return 0;
}
When you run the preceding console application, you get an output similar to the following:
An ImageCodecInfo object representing the PNG encoder
was found at position 4 in the array.
The CLSID of the PNG encoder is {557CF406-1A04-11D3-9A73-0000F81EF32E}.