Guys, i have finally found the reason why it was so slow.
I had no idea why it was so slow, even a Raspberry pi can run it at 30 FPS with no issues what so ever....
It turns out, 32 bpp on the GCW Zero is slow.
When i turned the depth to 16, it was much, much faster. It ran at like, 60 FPS.
However, the output was incorrect so the game was unplayable.
Cannonball was designed to work only in 32 bpp so i'll have to modify
the source code in order to have the correct output.
I have no idea how to do that so i'll just ask the author to help me.
Hopefully he's still around... If not, i might ask ptitseb instead.
Can I make a request? Could the rom folder be changed to be in /media/home/.cannonball/roms, instead of stranded outside? Keeps that folder more tidy and everything together.
I already did that, it will be in my next release.
EDIT:I have updated Cannonball.
This release should be a little faster : I used some optimisations from ptitseb, and i turned triple buffering on.
This is still not my final release, next release should run smoothly enough.
As requested by opt2not, you should now put your roms in /media/home/.cannonball/roms.
I have reintroduced the ability to change the framerate: fastest is 30 FPS and the slowest is 60 FPS.