public void OnViewportMouseUp(object sender, MouseButtonEventArgs args)
        {
            var pt = args.GetPosition(mainViewport);

            if (args.ChangedButton == MouseButton.Left)
            {
                m_transformMatrix.OnLBtnUp();
            }

            else if (args.ChangedButton == MouseButton.Right)
            {
                m_transformMatrix.OnRBtnUp();
            }
            else if (args.ChangedButton == MouseButton.XButton1 || args.ChangedButton == MouseButton.XButton2)
            {
                /*if (m_nChartModelIndex == -1) return;
                 * // 1. get the mesh structure related to the selection rect
                 * MeshGeometry3D meshGeometry = Computator.NET.Charting.Chart3D.Model3D.GetGeometry(mainViewport, m_nChartModelIndex);
                 * if (meshGeometry == null) return;
                 *
                 * // 2. set selection in 3d chart
                 * m_3dChart.Select(m_selectRect, m_transformMatrix, mainViewport);
                 *
                 * // 3. update selection display
                 * m_3dChart.HighlightSelection(meshGeometry, Color.FromRgb(200, 200, 200));*/
            }
        }