this is (maybe) (sometimes) called a dragonball
and was seen in many old amiga demos
(yes i own one; and i'm f*cking proud of it!)
like Desert Dreams by Kefrens [watch it!]...

                 
what i did is:
- make rotating lines...
- draw lines with z<0
- draw transparent circle
- draw lines with z>0 on top of it...
not too hard, is it?
thanx for the original math-routines have to go to
Tigerturtle (Christian Schmidt).