drawTextCentered method
Implementation
Size drawTextCentered(Canvas canvas, Offset c, String label,
TextStyle labelStyle, double maxwidth) {
final tp = measureText(label, labelStyle, maxwidth, TextAlign.center);
final offset = c + Offset(-tp.width / 2.0, -tp.height / 2.0);
tp.paint(canvas, offset);
return tp.size;
}