Not necessarily -- a lot of external hobbyist work has gone into reverse-engineering Sonic Generations, which has an official PC port and is based on the same e

Not necessarily -- a lot of external hobbyist work has gone into reverse-engineering Sonic Generations, which has an official PC port and is based on the same engine as Unleashed. Funnily enough, one of the most famous Generations mods is a project that ports over a bunch of levels from Unleashed. IIRC they changes the graphics pipeline to look and work more like the Unleashed one, too.