public TextBlock()
{
_painter = new TextPainter();
this.GetObservable(FontFamilyProperty).Subscribe(UpdateTypeface);
this.GetObservable(FontSizeProperty).Subscribe(v => _painter.FontSize = (float)v);
this.GetObservable(ForegroundProperty).Subscribe(
v => _painter.TextColor = (v as ISolidColorBrush)?.Color ?? default);
this.GetObservable(TextProperty).Subscribe(v => _painter.Source = TextSource.FromLaTeX(v));
}