decodeEncodedPolyline.dart

List<LatLng> decodeEncodedPolyline(String encoded) {
    List<LatLng> poly = [];
    int index = 0, len = encoded.length;
    int lat = 0, lng = 0;
    BigInt Big0 = BigInt.from(0);
    BigInt Big0x1f = BigInt.from(0x1f);
    BigInt Big0x20 = BigInt.from(0x20);

    while (index < len) {
      int shift = 0;
      BigInt b, result;
      result = Big0;
      do {
        b = BigInt.from(encoded.codeUnitAt(index++) - 63);
        result |= (b & Big0x1f) << shift;
        shift += 5;
      } while (b >= Big0x20);
      BigInt rshifted = result >> 1;
      int dlat;
      if (result.isOdd)
        dlat = (~rshifted).toInt();
      else
        dlat = rshifted.toInt();
      lat += dlat;

      shift = 0;
      result = Big0;
      do {
        b = BigInt.from(encoded.codeUnitAt(index++) - 63);
        result |= (b & Big0x1f) << shift;
        shift += 5;
      } while (b >= Big0x20);
      rshifted = result >> 1;
      int dlng;
      if (result.isOdd)
        dlng = (~rshifted).toInt();
      else
        dlng = rshifted.toInt();
      lng += dlng;

      poly.add(LatLng((lat / 1E5).toDouble(), (lng / 1E5).toDouble()));
    }
    return poly;
  }