>> There's a lot of oldish webpages with complex Bezier curve
>> constructions for circles.
>
> Those must be approximate constructions. It is not mathematically
> possible to construct a Bézier curve which is at the same time an
> exact circle.
Well, Metafont uses a third-order Bézier approximation to build up
circles (from four quarter circles). However, the Metafont book says
that the difference to a real circle is less than 0.06%, which is thus
imperceptible.
The same holds for PostScript-based fonts.
Werner
