NAME
        DrawEllipse -- draw an ellipse centered at cx,cy with vertical
           and horizontal radii of a,b respectively.

    SYNOPSIS
        DrawEllipse( rp, cx, cy, a, b )
                     a1  d0  d1  d2 d3

        void DrawEllipse( struct rastport *, short, short, short, short);

    FUNCTION
       Creates an elliptical outline within the rectangular region
        specified by the parameters, using the current foreground pen color.

    INPUTS
        rp - pointer to the rastport into which the ellipse will be drawn.
        cx - x coordinate of the centerpoint relative to the rastport.
        cy - y coordinate of the centerpoint relative to the rastport.
        a - the horizontal radius of the ellipse (note: a must be > 0)
        b - the vertical radius of the ellipse (note: b must be > 0)

    BUGS

    NOTES
        this routine does not clip the ellipse to a non-layered rastport.

    SEE ALSO
        DrawCircle macro
        graphics/gfxmacros.h
        graphics/rastport.h