/// <summary>
        /// Event handling for horizontal scroll bar. The image part will
        /// be adapted according to the position of horizontal scroll bar.
        /// </summary>
        private void hScrollBar1_Scroll(object sender, ScrollEventArgs e)
        {
            Rectangle rect = viewPort.ImagePart;

            rect.X = hScrollBar1.Value;
            hWndControl.setImagePart(rect.Y, rect.X,
                                     rect.Y + rect.Height,
                                     rect.X + rect.Width);
            hWndControl.repaint();
        }