protected void Gc_MouseUp(object sender, GLMouseEventArgs e)
        {
            SetViewScreenCoord(ref e);

            if (currentmouseover != null)
            {
                currentmouseover.MouseButtonsDown = GLMouseEventArgs.MouseButtons.None;

                SetControlLocation(ref e, currentmouseover);    // reset location etc

                if (currentmouseover.Enabled)
                {
                    currentmouseover.OnMouseUp(e);
                }
            }
            else
            {
                if (this.Enabled)               // not over any control (due to screen coord clip space), so send thru the displaycontrol
                {
                    this.OnMouseUp(e);
                }
            }

            mousedowninitialcontrol = null;
        }