onPaint method
Implementation
@override
void onPaint(PaintingContext context, Offset offset) {
context.canvas.save();
context.canvas.translate(center.dx, center.dy);
context.canvas.scale(animationFactor);
context.canvas.translate(-center.dx, -center.dy);
paintSegments(context, offset);
context.canvas.restore();
paintDataLabels(context, offset);
}