Custom circle render example

examples/custom-circle-render.html

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+---
+layout: example.html
+title: Custom Circle Render
+shortdesc: Example of a custom circle render.
+docs: >
+  This example demonstrates the use of 'ol/style/Style' render option function to render circle feature.
+tags: "circle, feature, vector, render, custom"
+---
+<div id="map" class="map"></div>

examples/custom-circle-render.js

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+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(coordinate, state) {
+      // eslint-disable-next-line no-console
+      console.log('This circle is rendered by the code below.', Date.now());
+      const [x, y, x1, y1] = coordinate;
+      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,
+  }),
+});