private void Selection_MouseDown(object sender, MouseButtonEventArgs e)
        {
            // double ckick = for some tools, this means "save selection"
            if (e.ClickCount == 2)
            {
                OnDoubleClick(e);
                return;
            }

            t_mobility  = SelectionMobility.CanMove;
            t_movePoint = new Point(e.GetPosition(t_container).X, e.GetPosition(t_container).Y);
        }
 private void T_selection_MouseLeave(object sender, MouseEventArgs e)
 {
     t_mobility = SelectionMobility.CannotMove;
 }
 private void Selection_MouseUp(object sender, MouseButtonEventArgs e)
 {
     t_mobility = SelectionMobility.CannotMove;
 }