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Example of some Regular Shape styles.

This example shows how several regular shapes or symbols (representing x, cross, star, triangle, square and stacked) can be created. A rectangle is produced by scaling a square created without rotation. Style stacked represents possility to stack multiple shapes with offset

main.js
import Feature from 'ol/Feature.js';
import Map from 'ol/Map.js';
import Point from 'ol/geom/Point.js';
import VectorLayer from 'ol/layer/Vector.js';
import VectorSource from 'ol/source/Vector.js';
import View from 'ol/View.js';
import {Fill, RegularShape, Stroke, Style} from 'ol/style.js';

const stroke = new Stroke({color: 'black', width: 2});
const fill = new Fill({color: 'red'});

const styles = {
  'square': new Style({
    image: new RegularShape({
      fill: fill,
      stroke: stroke,
      points: 4,
      radius: 10,
      angle: Math.PI / 4,
    }),
  }),
  'rectangle': new Style({
    image: new RegularShape({
      fill: fill,
      stroke: stroke,
      radius: 10 / Math.SQRT2,
      radius2: 10,
      points: 4,
      angle: 0,
      scale: [1, 0.5],
    }),
  }),
  'triangle': new Style({
    image: new RegularShape({
      fill: fill,
      stroke: stroke,
      points: 3,
      radius: 10,
      rotation: Math.PI / 4,
      angle: 0,
    }),
  }),
  'star': new Style({
    image: new RegularShape({
      fill: fill,
      stroke: stroke,
      points: 5,
      radius: 10,
      radius2: 4,
      angle: 0,
    }),
  }),
  'cross': new Style({
    image: new RegularShape({
      fill: fill,
      stroke: stroke,
      points: 4,
      radius: 10,
      radius2: 0,
      angle: 0,
    }),
  }),
  'x': new Style({
    image: new RegularShape({
      fill: fill,
      stroke: stroke,
      points: 4,
      radius: 10,
      radius2: 0,
      angle: Math.PI / 4,
    }),
  }),
  'stacked': [
    new Style({
      image: new RegularShape({
        fill: fill,
        stroke: stroke,
        points: 4,
        radius: 5,
        angle: Math.PI / 4,
        displacement: [0, 10],
      }),
    }),
    new Style({
      image: new RegularShape({
        fill: fill,
        stroke: stroke,
        points: 4,
        radius: 10,
        angle: Math.PI / 4,
      }),
    }),
  ],
};

const styleKeys = [
  'x',
  'cross',
  'star',
  'triangle',
  'square',
  'rectangle',
  'stacked',
];
const count = 250;
const features = new Array(count);
const e = 4500000;
for (let i = 0; i < count; ++i) {
  const coordinates = [2 * e * Math.random() - e, 2 * e * Math.random() - e];
  features[i] = new Feature(new Point(coordinates));
  features[i].setStyle(
    styles[styleKeys[Math.floor(Math.random() * styleKeys.length)]],
  );
}

const source = new VectorSource({
  features: features,
});

const vectorLayer = new VectorLayer({
  source: source,
});

const map = new Map({
  layers: [vectorLayer],
  target: 'map',
  view: new View({
    center: [0, 0],
    zoom: 2,
  }),
});

const colors = ['blue', 'green', 'yellow', 'aqua', 'red'];
let currentColor = 0;

document.getElementById('color-changer').addEventListener('click', function () {
  styles.square
    .getImage()
    .setFill(new Fill({color: colors[currentColor % colors.length]}));
  vectorLayer.changed();
  currentColor++;
});
index.html
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Regular Shapes</title>
    <link rel="stylesheet" href="node_modules/ol/ol.css">
    <style>
      .map {
        width: 100%;
        height: 400px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <div>
      <button id="color-changer">Change Square Colors</button>
    </div>

    <script type="module" src="main.js"></script>
  </body>
</html>
package.json
{
  "name": "regularshape",
  "dependencies": {
    "ol": "9.2.4"
  },
  "devDependencies": {
    "vite": "^3.2.3"
  },
  "scripts": {
    "start": "vite",
    "build": "vite build"
  }
}