paintTrendline method
Implementation
void paintTrendline(PaintingContext context, Offset offset) {
if (trendlineContainer != null &&
parent != null &&
parent!.render == SeriesRender.trendline) {
context.canvas.save();
context.canvas.clipRect(clipRect(paintBounds, animationFactor,
isInversed: xAxis!.isInversed, isTransposed: isTransposed));
context.paintChild(trendlineContainer!, offset);
context.canvas.restore();
}
}