/// <summary>
        /// Performs event handling of the HMouseWheel event of
        /// HWindowControl, so that the dipslayed image  part and scroll bars
        /// of HDisplayControl can be adapted to the current zoom value.
        /// </summary>
        private void viewPort_HMouseWheel(object sender, HMouseEventArgs e)
        {
            hWndControl.mouseWheel(sender, e);
            ManageScrollBars();
            hWndControl.repaint();

            this.Invalidate();
        }