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Earthquakes with custom symbols

Demonstrates the use of `toCanvas` to create custom icon symbols.

This example parses a KML file and renders the features as a vector layer. The layer is given a style that renders earthquake locations with a custom lightning symbol and a size relative to their magnitude.

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index.html<!DOCTYPE html>
<html lang="en">
  <head>
    <title>Earthquakes with custom symbols</title>
    <!-- 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>
    <style>
      .map {
        width: 100%;
        height:400px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <script src="index.js"></script>
  </body>
</html>
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index.jsimport 'ol/ol.css';
import Map from 'ol/Map';
import View from 'ol/View';
import KML from 'ol/format/KML';
import Polygon from 'ol/geom/Polygon';
import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer';
import {toContext} from 'ol/render';
import Stamen from 'ol/source/Stamen';
import VectorSource from 'ol/source/Vector';
import {Fill, Icon, Stroke, Style} from 'ol/style';


var symbol = [[0, 0], [4, 2], [6, 0], [10, 5], [6, 3], [4, 5], [0, 0]];
var scale;
var scaleFunction = function(coordinate) {
  return [coordinate[0] * scale, coordinate[1] * scale];
};

var styleCache = {};
var styleFunction = function(feature) {
  // 2012_Earthquakes_Mag5.kml stores the magnitude of each earthquake in a
  // standards-violating <magnitude> tag in each Placemark.  We extract it from
  // the Placemark's name instead.
  var name = feature.get('name');
  var magnitude = parseFloat(name.substr(2));
  var size = parseInt(10 + 40 * (magnitude - 5), 10);
  scale = size / 10;
  var style = styleCache[size];
  if (!style) {
    var canvas = document.createElement('canvas');
    var vectorContext = toContext(canvas.getContext('2d'),
      {size: [size, size], pixelRatio: 1});
    vectorContext.setStyle(new Style({
      fill: new Fill({color: 'rgba(255, 153, 0, 0.4)'}),
      stroke: new Stroke({color: 'rgba(255, 204, 0, 0.2)', width: 2})
    }));
    vectorContext.drawGeometry(new Polygon([symbol.map(scaleFunction)]));
    style = new Style({
      image: new Icon({
        img: canvas,
        imgSize: [size, size],
        rotation: 1.2
      })
    });
    styleCache[size] = style;
  }
  return style;
};

var vector = new VectorLayer({
  source: new VectorSource({
    url: 'data/kml/2012_Earthquakes_Mag5.kml',
    format: new KML({
      extractStyles: false
    })
  }),
  style: styleFunction
});

var raster = new TileLayer({
  source: new Stamen({
    layer: 'toner'
  })
});

var map = new Map({
  layers: [raster, vector],
  target: 'map',
  view: new View({
    center: [0, 0],
    zoom: 2
  })
});
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package.json{
  "name": "earthquake-custom-symbol",
  "dependencies": {
    "ol": "6.1.1"
  },
  "devDependencies": {
    "parcel": "1.11.0"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --experimental-scope-hoisting --public-url . index.html"
  }
}