objects are specified by center position and radius, and
are purely graphical with no electrical meaning. They can be drawn in
different colors, and with various stroke and fill settings.
See Object color. See Object fill and stroke.
Creates and returns a new circle
object. center is the position of the center of the new circle in the form
(x . y), and radius is the integer radius of the circle. If color is specified, it should be the integer color map index of the color with which to draw the circle. If color is not specified, the default circle color is used.
Sets the parameters of circle. The arguments are the same as to
make-circle. Returns circle.
Returns the parameters of circle as a list of the form:((center-x . center-y) radius color)
Returns the position of the center of circle as in the form
(x . y).