dart_jts 0.2.2+3

An ongoing effort to port the Java Topology Suite to the dart programming language and make it available to its mobile, dektop and web environments.

example/lib/main.dart

import 'package:dart_jts/dart_jts.dart';
import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'dart_jts example',
      home: ExamplePage(),
    );
  }
}

class ExamplePage extends StatefulWidget {
  @override
  _ExamplePageState createState() => _ExamplePageState();
}

class _ExamplePageState extends State<ExamplePage> {
  double buffer = 50;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Dart_JTS Example - Polygon Offset'),
      ),
      body: Center(
        child: ExampleShape(buffer: buffer,),
      ),
      bottomNavigationBar: BottomAppBar(
        child: SizedBox(
          height: 50,
          child: Slider(
            min: 0,
            max: 100,
            onChanged: (val){setState(() {
              buffer = val;
            });},
            value: buffer,
            divisions: 100,
            label: "${buffer.floor()}",
          ),
        )
      ),

    );
  }
}


class ExampleShape extends StatelessWidget{
  final double buffer;
  ExampleShape({@required this.buffer});

  @override
  Widget build(BuildContext context) {
    return CustomPaint(
      painter: ExampleShapePainter(buffer: buffer,shape: [
        Offset(-90,-200),
        Offset(120,-25),
        Offset(90,110),
        Offset(0,0),
        Offset(-120,25),
      ])
      );
  }
}

class ExampleShapePainter extends CustomPainter {
  final double buffer;
  final List<Offset> shape;

  ExampleShapePainter({@required this.buffer, @required this.shape}):
    assert(shape.length == 0 || shape.length >= 4);

  @override
  void paint(Canvas canvas, Size size) {
    Paint bodyPaint = Paint()
      ..color = Colors.blue
      ..style = PaintingStyle.fill;

    Paint inflatedPaint = Paint()
      ..color = Colors.orange
      ..style = PaintingStyle.fill;

    /// Draw inflated shape
    if(shape.length>=4) {
      GeometryFactory geometryFactory = GeometryFactory.defaultPrecision();

      /// Convert [List<Offset>] to [List<Coordinate>] to work with dart_jts
      List<Coordinate> coords = shape.map((element) => Coordinate(element.dx,element.dy)).toList();
      coords.add(coords.first); /// First and last coord MUST be identical
      LinearRing linearRing = LinearRing.withFactory(coords, geometryFactory);

      /// Create the polygon with no holes (hence the empty list as the 2nd argument)
      Polygon polygon = geometryFactory.createPolygon(linearRing, []);

      polygon = polygon.buffer(buffer);
      List<Offset> inflated = polygon.shell.points.toCoordinateArray().map((
          e) => Offset(e.x, e.y)).toList();

      Path inflatedPath = Path()
        ..addPolygon(inflated, true);

      debugPrint(inflated.toString());
      canvas.drawPath(
          inflatedPath, inflatedPaint);
    }

    /// Draw normal shape
    Path path = Path();
    path.addPolygon(shape, true);
    canvas.drawPath(path, bodyPaint);
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) => true;
}