protected void Gc_MouseWheel(object sender, GLMouseEventArgs e)
        {
            if (currentmouseover != null && currentmouseover.Enabled)
            {
                SetViewScreenCoord(ref e);
                SetControlLocation(ref e, currentmouseover);    // set location etc

                if (currentmouseover.Enabled)
                {
                    currentmouseover.OnMouseWheel(e);
                }
            }
        }