总算知道怎样从ImageMagick生成的数据转换成HICON: MagickGetImageBlob & LookupIconIdFromDirectoryEx

MagickSetImageFormat(mw, "ICO"); //设置这个后, MagickGetImageBlob 才能返回正确的值

size_t length;
PBYTE pIcoData = MagickGetImageBlob(mw, &length);
 //printf("length:%ld\n", length);

 //HICON hIcon = NULL;
 int offset = LookupIconIdFromDirectoryEx(pIcoData, TRUE, width_thumbnail, height_thumbnail, LR_DEFAULTCOLOR);
 //printf("offset:%d\n", offset);

if(offset != )
 {
    *hIcon = CreateIconFromResourceEx(pIcoData + offset, , TRUE, 0x30000, width_thumbnail, height_thumbnail, LR_DEFAULTCOLOR);
}

MagickRelinquishMemory(pIcoData); //注意Blob使用完后,释放内存