Custom polygon styles (style func)

by Vladimir Vershinin

HTML

<script src="https://unpkg.com/vue@latest/dist/vue.min.js"></script>
<script src="https://cdn.jsdelivr.net/gh/openlayers/openlayers.github.io/en/v5.3.0/build/ol.js"></script>
<script src="https://unpkg.com/[email protected]/lib/index.umd.js"></script>
<link rel="stylesheet" href="https://unpkg.com/[email protected]/lib/style.css">
<div id="app">
  <vl-map ref="map">
    <vl-view :zoom.sync="zoom" :center.sync="center"></vl-view>
    
    <vl-layer-vector>
      <vl-source-vector :features.sync="geojsonObject.features" />
      <vl-style-func :factory="styleFuncFactory" />
    </vl-layer-vector>
  </vl-map>  
</div>

CSS

html, body, #app {
  width: 100%;
  height: 100%;
  margin: 0;
  padding: 0;
}

JavaScript

let geojsonObject = {
  'type': 'FeatureCollection',
  'crs': {
    'type': 'name',
    'properties': {
      'name': 'EPSG:3857'
    }
  },
  'features': [{
  	'id': 1,
    'type': 'Feature',
    'geometry': {
      'type': 'Polygon',
      'coordinates': [[[-5e6, 6e6], [-5e6, 8e6], [-3e6, 8e6],
                       [-3e6, 6e6], [-5e6, 6e6]]]
    }
  }, {
  	'id': 2,
    'type': 'Feature',
    'geometry': {
      'type': 'Polygon',
      'coordinates': [[[-2e6, 6e6], [-2e6, 8e6], [0, 8e6],
                       [0, 6e6], [-2e6, 6e6]]]
    }
  }, {
  	'id': 3,
    'type': 'Feature',
    'geometry': {
      'type': 'Polygon',
      'coordinates': [[[1e6, 6e6], [1e6, 8e6], [3e6, 8e6],
                       [3e6, 6e6], [1e6, 6e6]]]
    }
  }, {
  	'id': 4,
    'type': 'Feature',
    'geometry': {
      'type': 'Polygon',
      'coordinates': [[[-2e6, -1e6], [-1e6, 1e6],
                       [0, -1e6], [-2e6, -1e6]]]
    }
  }]
};

new Vue({
	el: '#app',
  data () {
  	return {
    	zoom: 2,
      center: [0, 3000000],
      geojsonObject: geojsonObject,
    }
  },
  methods: {
  	styleFuncFactory () {
    	return feature => {
        return [
          /* We are using two different styles for the polygons:
           *  - The first style is for the polygons themselves.
           *  - The second style is to draw the vertices of the polygons.
           *    In a custom `geometry` function the vertices of a polygon are
           *    returned as `MultiPoint` geometry, which will be used to render
           *    the style.
           */
          new ol.style.Style({
            stroke: new ol.style.Stroke({
              color: 'blue',
              width: 3
            }),
            fill: new ol.style.Fill({
              color: 'rgba(0, 0, 255, 0.1)'
            })
          }),
          new ol.style.Style({
            image: new ol.style.Circle({
              radius: 5,
              fill: new ol.style.Fill({
                color: 'orange'
          ...