onPaint method
Draws segment in series bounds.
Implementation
@override
void onPaint(Canvas canvas) {
  final Paint paint = getStrokePaint();
  if (paint.color != Colors.transparent && paint.strokeWidth > 0) {
    canvas.drawPath(_verticalPath, paint);
    canvas.drawPath(_verticalCapPath, paint);
    canvas.drawPath(_horizontalPath, paint);
    canvas.drawPath(_horizontalCapPath, paint);
  }
}