A circle just an ellipse with equal graphical<-width
and graphical<-height.
It's border-line may have a graphical<-texture
and graphical<-pen.
The circle's interior may be filled with an image
object using circle->fill.
|{foreground,background}*Defaults: @nil (transparent).
<-diameter<-width
or graphical<-height
is specified this value is used for both parameters. If both are
specified the minimum of the two is used for both.<-radius<-width and graphical<-height
to this value. See also circle->radius.<-width. circle->radius
sets graphical<-width and graphical<-height
to twice the argument.