如何在google地图上绘制两个点之间的部分路径？

<script src="https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY"></script>

<div id="map"></div>

var map = new google.maps.Map(document.getElementById('map'), {
  center: {lat: YOUR_LATITUDE, lng: YOUR_LONGITUDE},
  zoom: ZOOM_LEVEL
});

var marker1 = new google.maps.Marker({
  position: {lat: LATITUDE_1, lng: LONGITUDE_1},
  map: map,
  title: 'Marker 1'
});

var marker2 = new google.maps.Marker({
  position: {lat: LATITUDE_2, lng: LONGITUDE_2},
  map: map,
  title: 'Marker 2'
});

var directionsService = new google.maps.DirectionsService();
var directionsRenderer = new google.maps.DirectionsRenderer();

directionsRenderer.setMap(map);

var request = {
  origin: {lat: LATITUDE_1, lng: LONGITUDE_1},
  destination: {lat: LATITUDE_2, lng: LONGITUDE_2},
  travelMode: 'DRIVING'
};

directionsService.route(request, function(result, status) {
  if (status == 'OK') {
    directionsRenderer.setDirections(result);
  }
});