Google Maps for Flutter Polyline Decoding

polyline_decode.dart

import 'package:google_maps_flutter/google_maps_flutter.dart';

List<LatLng> polylineDecode(String polyline) {
  final codeUnits = polyline.codeUnits;
  final len = codeUnits.length;

  // For speed we preallocate to an upper bound on the final length, then
  // truncate the array before returning.
  final path = <LatLng>[];
  var index = 0;
  var lat = 0;
  var lng = 0;

  while (index < len) {
    var result = 1;
    var shift = 0;
    int b;
    do {
      b = codeUnits[index++] - 63 - 1;
      result += b << shift;
      shift += 5;
    } while (b >= 0x1f);
    lat += (result & 1 != 0) ? ~(result >> 1) : result >> 1;

    result = 1;
    shift = 0;
    do {
      b = codeUnits[index++] - 63 - 1;
      result += b << shift;
      shift += 5;
    } while (b >= 0x1f);
    lng += (result & 1 != 0) ? ~(result >> 1) : result >> 1;

    path.add(LatLng(lat * 1e-5, lng * 1e-5));
  }

  return path;
}