Custom Circle Render

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Example of a custom circle render.

This example demonstrates the use of 'ol/style/Style' render option function to render circle feature.

main.js

import Feature from 'ol/Feature.js';
import Map from 'ol/Map.js';
import View from 'ol/View.js';
import {Circle} from 'ol/geom.js';
import {OSM, Vector as VectorSource} from 'ol/source.js';
import {Style} from 'ol/style.js';
import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer.js';

const circleFeature = new Feature({
  geometry: new Circle([12127398.797692968, 4063894.123105166], 50),
});
circleFeature.setStyle(
  new Style({
    renderer(coordinates, state) {
      const [[x, y], [x1, y1]] = coordinates;
      const ctx = state.context;
      const dx = x1 - x;
      const dy = y1 - y;
      const radius = Math.sqrt(dx * dx + dy * dy);

      const innerRadius = 0;
      const outerRadius = radius * 1.4;

      const gradient = ctx.createRadialGradient(
        x,
        y,
        innerRadius,
        x,
        y,
        outerRadius,
      );
      gradient.addColorStop(0, 'rgba(255,0,0,0)');
      gradient.addColorStop(0.6, 'rgba(255,0,0,0.2)');
      gradient.addColorStop(1, 'rgba(255,0,0,0.8)');
      ctx.beginPath();
      ctx.arc(x, y, radius, 0, 2 * Math.PI, true);
      ctx.fillStyle = gradient;
      ctx.fill();

      ctx.arc(x, y, radius, 0, 2 * Math.PI, true);
      ctx.strokeStyle = 'rgba(255,0,0,1)';
      ctx.stroke();
    },
  }),
);

new Map({
  layers: [
    new TileLayer({
      source: new OSM(),
      visible: true,
    }),
    new VectorLayer({
      source: new VectorSource({
        features: [circleFeature],
      }),
    }),
  ],
  target: 'map',
  view: new View({
    center: [12127398.797692968, 4063894.123105166],
    zoom: 19,
  }),
});

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Custom Circle Render</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>

    <script type="module" src="main.js"></script>
  </body>
</html>

package.json

{
  "name": "custom-circle-render",
  "dependencies": {
    "ol": "9.1.0"
  },
  "devDependencies": {
    "vite": "^3.2.3"
  },
  "scripts": {
    "start": "vite",
    "build": "vite build"
  }
}