> If an open-source implementation of the engine doesn't exist, you're always free to write one.
This is a very strange interpretation.
When a piece of software that is released under a free license has a crucial non-free dependency, it is effectively non-free. As the software only works with the non-free dependency, but that dependency cannot be conveyed along with the free part, the whole thing cannot legally be distributed and thus is non-free.
This is a very strange interpretation.
When a piece of software that is released under a free license has a crucial non-free dependency, it is effectively non-free. As the software only works with the non-free dependency, but that dependency cannot be conveyed along with the free part, the whole thing cannot legally be distributed and thus is non-free.