Two functions are associated with drawing ellipses: drawcircle() and
drawellipse(). drawcircle(), a macro that calls drawellipse(), will draw a
circle from the specified center point using the specified radius.  This
function is executed by the statement:

    DrawCircle(&rastPort, center_x, center_y, radius);

Similarly, drawellipse() draws an ellipse with the specified radii from
the specified center point:

    DrawEllipse(&rastPort, center_x, center_y, horiz_r, vert_r);

Neither function performs clipping on a non-layered rastport.