Aaron Giles was just lamenting the other day that the GDI ellipse drawing is apparently slightly lopsided, since he's trying to recreate it :)
[1] I can't take much credit. The code was Bresenham's algorithm, as explained to me by the OS/2 group. At the time, OS/2 was the cool operating system that was the wave of the future and Windows was this obscure operating system that nobody cared about. The impression I got was that the OS/2 people didn't really want to waste their time talking to us.