System.Windows.Forms.TreeView.OnMouseMove C# (CSharp) Method

        protected override void OnMouseMove(MouseEventArgs e)
        {
            if (_scroll)
            {
                var mclient = PointToClient(MousePosition);

                scrollIndex = (mclient.Y - _scrollStartY) * (_scroll_ItemsEstimatedHeigh / Height);

                _FixScrollIndex();
                _UpdateScrollList();
            }
            if (_drag)
            {
                if (_dragPosition.Distance(e.Location) > 4)
                {
                    ItemDrag(this, new ItemDragEventArgs(e.Button, _dragNode));
                    _dragPosition = Point.Empty;
                    _drag = false;
                }
            }
        }
        protected override void OnMouseWheel(MouseEventArgs e)