public enum DrawingOutlineType : System.Enum, System.IComparable, System.IConvertible, System.IFormattable, System.ISpanFormattable  

{
    if (featureLayer == null)
        return;

    var mv = MapView.Active;
    //Note: Run within a QueuedTask
    using (var table = featureLayer.GetTable())
    {
        using (var rc = table.Search())
        {
            //get the first feature...
            //...assuming at least one feature gets retrieved
            rc.MoveNext();
            var oid = rc.Current.GetObjectID();

            //Use DrawingOutlineType.BoundingEnvelope to retrieve a generalized
            //mask geometry or "Box". The mask will be in the same SpatRef as the map
            var mask_geom = featureLayer.GetDrawingOutline(oid, mv, DrawingOutlineType.Exact);

            //TODO - use the mask geometry...
        }
    }
}