( resource psdoc, float x, float y, float radius, float alpha, float beta )
Draws a portion of a circle with at middle point at
(x, y). The arc starts at an
angle of alpha and ends at an angle of
beta. It is drawn counterclockwise (use
ps_arcn() to draw clockwise). The subpath added
to the current path starts on the arc at angle alpha
and ends on the arc at angle beta.