import 'dart:ui' as ui;

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Nine Slice Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Nine Slice Demo'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  ui.Image theImage;
  double size = 200.0;

  @override
  void initState() {
    super.initState();
    makeImage().then((image) => setState(() {
      theImage = image;
    }));
  }

  void newSize(double newSize) {
    setState(() {
      size = newSize;
    });
  }

  Future<ui.Image> makeImage() {
    Rect bounds = Rect.fromLTWH(0, 0, 200, 200);
    ui.PictureRecorder recorder = ui.PictureRecorder();
    Canvas canvas = Canvas(recorder, bounds);
    paintCheckerboard(canvas, bounds, 10, 10, Colors.white, Colors.grey);
    paintCheckerboard(canvas, bounds.deflate(50), 10, 10, Colors.blue, Colors.green);
    return recorder.endRecording().toImage(200, 200);
  }

  paintCheckerboard(Canvas canvas, Rect bounds, double w, double h, Color c1, Color c2) {
    Paint p = Paint();
    double y = bounds.top;
    for (int i = 0; i < bounds.height / h; i++) {
      double x = bounds.left;
      for (int j = 0; j < bounds.width / w; j++) {
        p.color = (i ^ j) & 1 == 0 ? c1 : c2;
        canvas.drawRect(Rect.fromLTWH(x, y, w, h), p);
        x += w;
      }
      y += h;
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: theImage == null ? null : CustomPaint(
          size: Size(size, size),
          painter: NineSlicePainter(
            theImage,
            const Rect.fromLTWH(50, 50, 100, 100),
            Rect.fromLTWH(0, 0, size, size),
          ),
          willChange: false,
          isComplex: false,
        ),
      ),
      bottomNavigationBar: BottomAppBar(
        child: Wrap(
          children: [
            Slider(
              value: size,
              min: 50,
              max: 300,
              onChanged: theImage == null ? null : newSize,
            ),
          ],
        ),
      ),
    );
  }
}

class NineSlicePainter extends CustomPainter {
  NineSlicePainter(this.theImage, this.center, this.dst);

  Rect center;
  Rect dst;
  ui.Image theImage;

  @override
  void paint(Canvas canvas, Size size) {
    canvas.drawImageNine(theImage, center, dst, Paint());
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) {
    if (oldDelegate is NineSlicePainter) {
      return oldDelegate.dst != dst || oldDelegate.theImage != theImage;
    }
    return true;
  }
}