paint method
Implementation
void paint(Canvas canvas) {
final Paint _painter = Paint()
..color = innerRectColor
..style = PaintingStyle.stroke
..strokeWidth = innerRectStrokeWidth;
final Rect innerRect = ui.Rect.fromLTRB(region.x1.toDouble(),
region.y1.toDouble(), region.x2.toDouble(), region.y2.toDouble());
canvas.drawRect(innerRect, _painter);
}