custom-circle-render.js

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