System.Windows.Forms.TreeView_Old.OnMouseWheel C# (CSharp) Method

        protected override void OnMouseWheel(MouseEventArgs e)
        {
            base.OnMouseWheel(e);
            _scrollIndex -= e.Delta;
            _scrollIndex = _scrollIndex < 0 ? 0 : _scrollIndex;
            _scrollIndex = _scrollIndex > _scrollItems - _renderList.Count ? _scrollItems - _renderList.Count : _scrollIndex;

            Refresh();
        }
        protected override void OnPaint(PaintEventArgs e)