MexThumbnailCallback ()

void                (*MexThumbnailCallback)             (const char *uri,
                                                         gpointer user_data);

mex_thumbnailer_generate ()

void                mex_thumbnailer_generate            (const char *uri,
                                                         const char *mime_type,
                                                         MexThumbnailCallback callback,
                                                         gpointer user_data);

Attempt to generate a thumbnail for url asynchronously. When thumbnailing is complete, callback is called. If thumbnailing isn't possible or fails no callback will be made, so it is recommended to set a fallback image before calling this function.