@Tcheko
Thank you for your reply. I am afraid it doesn't help because that would mean I should change the way the application is developed, and do that on every update. I wonder if anyone ported it for any other project, but never released it to the public.

If there is no version, I found in Aminet an Aros port, and I might work with that to port the library to MorphOS (https://aminet.net/package/dev/lib/agg.src-aros). I guess that version would be pretty close to what a MorphOS one should be, right?

Any recommendations by anyone?