javascript - Google Map API v3 shade everything EXCEPT for polygon

Question

So by now we're familiar with adding shapes to a Google map with the v3 API:

$j('#map').gmap('addShape', 'Circle', { 
    'strokeWeight': 0, 
    'fillColor': "#008595", 
    'fillOpacity': 0.25, 
    'center': result[0].geometry.location, 
    'radius': 1500, 
    'clickable': false 
});

The above code will create a circle and shade it with fill #008595. Is there any way to inversely shade a map? I would like the entire world to be shaded/filled at half opacity except for a hole where my markers are. Possible?

Answer 1

you need to define a polygon that covers the whole world and has a hole in it, you can't do it with the "Circle" or "Rectangle" shapes, it has to be a polygon with (at least) two paths.

here is an example

related questions:

• Change map opacity outside circle of Google Maps JavaScript API v3
• Highlight polygon and tint rest of map using Google Maps

code snippet:

// This example creates circles on the map, representing
// populations in the United States.

// First, create an object containing LatLng and population for each city.
var citymap = {};
citymap['chicago'] = {
  center: new google.maps.LatLng(41.878113, -87.629798),
  population: 2842518
};
citymap['newyork'] = {
  center: new google.maps.LatLng(40.714352, -74.005973),
  population: 8143197
};
citymap['losangeles'] = {
  center: new google.maps.LatLng(34.052234, -118.243684),
  population: 3844829
};
var cityCircle;
var bounds = new google.maps.LatLngBounds();

function drawCircle(point, radius, dir) {
  var d2r = Math.PI / 180; // degrees to radians 
  var r2d = 180 / Math.PI; // radians to degrees 
  var earthsradius = 3963; // 3963 is the radius of the earth in miles
  var points = 32;

  // find the raidus in lat/lon 
  var rlat = (radius / earthsradius) * r2d;
  var rlng = rlat / Math.cos(point.lat() * d2r);

  var extp = new Array();
  if (dir == 1) {
    var start = 0;
    var end = points + 1
  } // one extra here makes sure we connect the ends
  else {
    var start = points + 1;
    var end = 0
  }
  for (var i = start;
    (dir == 1 ? i < end : i > end); i = i + dir) {
    var theta = Math.PI * (i / (points / 2));
    ey = point.lng() + (rlng * Math.cos(theta)); // center a + radius x * cos(theta) 
    ex = point.lat() + (rlat * Math.sin(theta)); // center b + radius y * sin(theta) 
    extp.push(new google.maps.LatLng(ex, ey));
    bounds.extend(extp[extp.length - 1]);
  }
  return extp;
}

function initialize() {
  // Create the map.
  var mapOptions = {
    zoom: 4,
    center: new google.maps.LatLng(37.09024, -95.712891),
    mapTypeId: google.maps.MapTypeId.TERRAIN
  };

  var map = new google.maps.Map(document.getElementById('map-canvas'),
    mapOptions);

  var outerbounds = [
    new google.maps.LatLng(85, 180),
    new google.maps.LatLng(85, 90),
    new google.maps.LatLng(85, 0),
    new google.maps.LatLng(85, -90),
    new google.maps.LatLng(85, -180),
    new google.maps.LatLng(0, -180),
    new google.maps.LatLng(-85, -180),
    new google.maps.LatLng(-85, -90),
    new google.maps.LatLng(-85, 0),
    new google.maps.LatLng(-85, 90),
    new google.maps.LatLng(-85, 180),
    new google.maps.LatLng(0, 180),
    new google.maps.LatLng(85, 180)
  ];
  var populationOptions = {
    strokeColor: '#FF0000',
    strokeOpacity: 0.8,
    strokeWeight: 2,
    fillColor: '#FF0000',
    fillOpacity: 0.35,
    map: map,
    paths: [outerbounds, drawCircle(citymap['newyork'].center, 10, -1)]
  };
  // Add the circle for this city to the map.
  cityCircle = new google.maps.Polygon(populationOptions);
  map.fitBounds(bounds);
}

google.maps.event.addDomListener(window, 'load', initialize);

html,
body,
#map-canvas {
  height: 100%;
  margin: 0px;
  padding: 0px
}

<script src="https://maps.googleapis.com/maps/api/js?key=AIzaSyCkUOdZ5y7hMm0yrcCQoCvLwzdM6M8s5qk"></script>
<div id="map-canvas"></div>