paint method
This will paint on the screen
Implementation
@override
void paint(Canvas canvas, Size size) {
TextSpan span = new TextSpan(
style: new TextStyle(
color: Colors.lightGreenAccent,
fontSize: 24.0,
fontFamily: 'Roboto'),
text: "$fps");
TextPainter tp = new TextPainter(
text: span,
textAlign: TextAlign.left,
textDirection: TextDirection.ltr);
tp.layout();
tp.paint(canvas, new Offset(0, 0));
}