protected override IList <object> Pick(MouseEventArgs e)
        {
            bool          multiSelect = DragOverThreshold;
            List <object> paths       = new List <object>();

            HitRecord[] hits;


            if (multiSelect)
            {// frustum pick
                RectangleF rect = MakeRect(FirstMousePoint, CurrentMousePoint);
                hits = GameEngine.FrustumPick(SurfaceId, Camera.ViewMatrix, Camera.ProjectionMatrix, rect);
            }
            else
            {// ray pick
                Ray3F rayW = GetWorldRay(CurrentMousePoint);
                hits = GameEngine.RayPick(Camera.ViewMatrix, Camera.ProjectionMatrix, rayW, false);
            }

            // create unique list of hits
            HashSet <ulong>  instanceSet = new HashSet <ulong>();
            List <HitRecord> uniqueHits  = new List <HitRecord>();

            // build 'path' objects for each hit record.
            foreach (HitRecord hit in hits)
            {
                bool added = instanceSet.Add(hit.instanceId);
                if (added)
                {
                    uniqueHits.Add(hit);
                }
            }

            HitRecord firstHit = new HitRecord();


            // build 'path' objects for each hit record.
            foreach (HitRecord hit in uniqueHits)
            {
                NativeObjectAdapter nobj = GameEngine.GetAdapterFromId(hit.instanceId);
                DomNode             dom  = nobj.DomNode;
                object hitPath           = Util.AdaptDomPath(dom);
                object obj = DesignView.PickFilter.Filter(hitPath, e);
                if (obj != null)
                {
                    if (paths.Count == 0)
                    {
                        firstHit = hit;
                    }
                    var newPath = obj as AdaptablePath <object> ?? Util.AdaptDomPath((DomNode)obj);
                    paths.Add(newPath);
                }
            }


            if (multiSelect == false && paths.Count > 0)
            {
                var path = paths[0];
                ISelectionContext selection = DesignView.Context.As <ISelectionContext>();
                ILinear           linear    = path.As <ILinear>();
                if (linear != null &&
                    Control.ModifierKeys == System.Windows.Forms.Keys.Shift &&
                    selection.SelectionContains(path))
                {
                    ITransactionContext trans = DesignView.Context.As <ITransactionContext>();
                    trans.DoTransaction(
                        delegate
                    {
                        linear.InsertPoint(firstHit.index, firstHit.hitPt.X, firstHit.hitPt.Y, firstHit.hitPt.Z);
                    }, "insert control point".Localize()
                        );
                }
            }
            return(paths);
        }