You are correct. Much better arc drawing code is present in MacX than is
present in many X11 servers. On machines that have a floating point unit
(all Mac II-class machines, Macintosh SE, and Macintosh IIsi with FPU
installed), MacX uses this hardware to achieve good arc-drawing
performance. Without an FPU, MacX uses SANE to do its floating point, but
it is still pretty fast. Thick lines are slow. Actually, pretty much the
same arc-drawing code appears in MacX 1.0 as in MacX 1.1.