WebGL Layer is an experimental extension of Google Maps to provide support for WebGL integration and data manipulation. WebGL Layer provides you with:
- Ability to load GeoJSON data and display with WebGL.
- Ability to alter some properties of loaded data (i.e color).
- Ability to define custom shaders and properties on data.
- Ability to plug into a vector tile server for data.
WebGL Layer has a few core dependencies that need to be included.
- CanvasLayer - provides a HTML5 canvas on top of a map which WebGL Layer uses to run a WebGL context
- Libtess.js - Javascript port of the GLUTesselate library. For super speedy Tesselation of Polygons.
- ShaderProgram.js - Utility library for management of WebGL variables and uniforms.
This example shows how to create a WebGL Layer object and begin the rendering loop.
<head>
<script type="text/javascript" src="//maps.googleapis.com/maps/api/js?libraries=places,drawing"></script>
<!-- Import WebGL Layer and Dependencies. -->
<script src="../CanvasLayer.js"></script>
<script src="../ShaderProgram.js"></script>
<script src="../libtess.cat.js"></script>
<script src="../WebGLLayer.js"></script>
<script>
var map;
var myLayer;
function init(){
var mapOptions = {
zoom: 12,
center: new google.maps.LatLng(51.50711, -0.123124),
mapTypeId: google.maps.MapTypeId.ROADMAP,
};
var mapCanvas = document.getElementById('map-canvas');
map = new google.maps.Map(mapCanvas, mapOptions);
myLayer = new WebGLLayer(map);
myLayer.start();
}
</script>
</head>
<body>
<div id="map-canvas"></div>
</body>
From a file:
var myLayer = new WebGLLayer(map);
//Loading GeoJSON from application.
myLayer.loadData({"type": "FeatureCollection", features: {..}});
//Loading GeoJSON from an external source.
myLayer.loadGeoJson(‘//myserver.co.uk/my.geo.json’);
myLayer.start();
From a tileserver:
var myLayer = new WebGLLayer(map);
//Expects a base of a tileserver URL, i.e something that can be appended to to make a full tile URL.
myLayer.tilebase(‘//tileserver.com/layer/’);
//optional attribute that forces WebGL Layer to only load tiles at a certain zoom level,
myLayer.zoomlock = 12;
myLayer.start();
Using the featureAdded callback you can add your features into other libraries such as Crossfilter and JSTS.
var myLayer = new WebGLLayer(map);
var index = new jsts.index.strtree.STRtree();
var reader = new jsts.io.GeoJSONReader();
myLayer.onAddFeature = function(feature){
var feat = reader.read(feature);
index.insert(feat.geometry.getEnvelopeInternal(), feat);
}
You can then run powerful queries on the data and use the index property on the returned feature to change data in the WebGL Layer
var result = ... //Query result.
var idx = result.properties.index;
myLayer.changePointColor(idx, [0., 0., 1.]); //Change color to blue
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