private void Grid_MouseDown(object sender, MouseButtonEventArgs e)
        {
            if (t_selectionMade == false)
            {
                // creates the selection rectangle and adds it to the container
                t_selection              = new PaintualUI.Controls.SelectionRectangle(Glass, e.GetPosition(this), t_zoomFactor);
                t_selection.DoubleClick += T_selection_DoubleClick;

                t_drawingMode = Engine.DrawingBoardModes.Draw;
            }
        }
        private void Grid_MouseUp(object sender, MouseButtonEventArgs e)
        {
            // this can happen when user moves mouse over drawign board before clicking the Apply button
            if (t_selection == null)
            {
                return;
            }

            t_selectionMade         = true;
            t_drawingMode           = Engine.DrawingBoardModes.None;
            t_selection.AllowResize = true;
        }