protected override void OnRender(DrawingContext drawingContext)
        {
            base.OnRender(drawingContext);
            //equationRoot.DrawEquation(drawingContext);
            ScrollViewer scrollViewer = Parent as ScrollViewer;

            equationRoot.DrawVisibleRows(drawingContext, scrollViewer.VerticalOffset, scrollViewer.ViewportHeight + scrollViewer.VerticalOffset);
        }