Symbols with WebGL

Using symbols in an atlas with WebGL.

When using symbol styles with WebGL, OpenLayers would render the symbol on a temporary image and would create a WebGL texture for each image. For a better performance, it is recommended to use atlas images (similar to image sprites with CSS), so that the number of textures is reduced. OpenLayers provides an AtlasManager, which when passed to the constructor of a symbol style, will create atlases for the symbols.

<!DOCTYPE html>
<html>
  <head>
    <title>Symbols with WebGL</title>
    <link rel="stylesheet" href="https://openlayers.org/en/v4.6.4/css/ol.css" type="text/css">
    <!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
    <script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script>
    <script src="https://openlayers.org/en/v4.6.4/build/ol.js"></script>
  </head>
  <body>
    <div id="map" class="map"></div>
    <script>
      var atlasManager = new ol.style.AtlasManager({
        // we increase the initial size so that all symbols fit into
        // a single atlas image
        initialSize: 512
      });

      var symbolInfo = [{
        opacity: 1.0,
        scale: 1.0,
        fillColor: 'rgba(255, 153, 0, 0.4)',
        strokeColor: 'rgba(255, 204, 0, 0.2)'
      }, {
        opacity: 0.75,
        scale: 1.25,
        fillColor: 'rgba(70, 80, 224, 0.4)',
        strokeColor: 'rgba(12, 21, 138, 0.2)'
      }, {
        opacity: 0.5,
        scale: 1.5,
        fillColor: 'rgba(66, 150, 79, 0.4)',
        strokeColor: 'rgba(20, 99, 32, 0.2)'
      }, {
        opacity: 1.0,
        scale: 1.0,
        fillColor: 'rgba(176, 61, 35, 0.4)',
        strokeColor: 'rgba(145, 43, 20, 0.2)'
      }];

      var radiuses = [3, 6, 9, 15, 19, 25];
      var symbolCount = symbolInfo.length * radiuses.length * 2;
      var symbols = [];
      var i, j;
      for (i = 0; i < symbolInfo.length; ++i) {
        var info = symbolInfo[i];
        for (j = 0; j < radiuses.length; ++j) {
          // circle symbol
          symbols.push(new ol.style.Circle({
            opacity: info.opacity,
            scale: info.scale,
            radius: radiuses[j],
            fill: new ol.style.Fill({
              color: info.fillColor
            }),
            stroke: new ol.style.Stroke({
              color: info.strokeColor,
              width: 1
            }),
            // by passing the atlas manager to the symbol,
            // the symbol will be added to an atlas
            atlasManager: atlasManager
          }));

          // star symbol
          symbols.push(new ol.style.RegularShape({
            points: 8,
            opacity: info.opacity,
            scale: info.scale,
            radius: radiuses[j],
            radius2: radiuses[j] * 0.7,
            angle: 1.4,
            fill: new ol.style.Fill({
              color: info.fillColor
            }),
            stroke: new ol.style.Stroke({
              color: info.strokeColor,
              width: 1
            }),
            atlasManager: atlasManager
          }));
        }
      }

      var featureCount = 50000;
      var features = new Array(featureCount);
      var feature, geometry;
      var e = 25000000;
      for (i = 0; i < featureCount; ++i) {
        geometry = new ol.geom.Point(
            [2 * e * Math.random() - e, 2 * e * Math.random() - e]);
        feature = new ol.Feature(geometry);
        feature.setStyle(
            new ol.style.Style({
              image: symbols[i % symbolCount]
            })
        );
        features[i] = feature;
      }

      var vectorSource = new ol.source.Vector({
        features: features
      });
      var vector = new ol.layer.Vector({
        source: vectorSource
      });

      var map = new ol.Map({
        renderer: /** @type {Array<ol.renderer.Type>} */ (['webgl', 'canvas']),
        layers: [vector],
        target: document.getElementById('map'),
        view: new ol.View({
          center: [0, 0],
          zoom: 4
        })
      });
    </script>
  </body>
</html>