原文链接及内容

原文链接：https://openlayers.org/en/latest/examples/feature-animation.html

运行界面

这个例子展示了如何使用postrender和vectorContext对要素进行动画处理。在这里，我们选择做一个每次要素被添加到图层的闪光动画。

main.js代码如下：

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import Feature from 'ol/Feature.js';
import Map from 'ol/Map.js';
import Point from 'ol/geom/Point.js';
import View from 'ol/View.js';
import {Circle as CircleStyle, Stroke, Style} from 'ol/style.js';
import {OSM, Vector as VectorSource} from 'ol/source.js';
import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer.js';
import {easeOut} from 'ol/easing.js';
import {fromLonLat} from 'ol/proj.js';
import {getVectorContext} from 'ol/render.js';
import {unByKey} from 'ol/Observable.js';

const tileLayer = new TileLayer({
  source: new OSM({
    wrapX: false,
  }),
});

const source = new VectorSource({
  wrapX: false,
});
const vector = new VectorLayer({
  source: source,
});

const map = new Map({
  layers: [tileLayer, vector],
  target: 'map',
  view: new View({
    center: [0, 0],
    zoom: 1,
    multiWorld: true,
  }),
});

function addRandomFeature() {
  const x = Math.random() * 360 - 180;
  const y = Math.random() * 170 - 85;
  const geom = new Point(fromLonLat([x, y]));
  const feature = new Feature(geom);
  source.addFeature(feature);
}

const duration = 3000;
function flash(feature) {
  const start = Date.now();
  const flashGeom = feature.getGeometry().clone();
  const listenerKey = tileLayer.on('postrender', animate);

  function animate(event) {
    const frameState = event.frameState;
    const elapsed = frameState.time - start;
    if (elapsed >= duration) {
      unByKey(listenerKey);
      return;
    }
    const vectorContext = getVectorContext(event);
    const elapsedRatio = elapsed / duration;
    // radius will be 5 at start and 30 at end.
    // 起始半径为5，结束半径为30。
    const radius = easeOut(elapsedRatio) * 25 + 5;
    const opacity = easeOut(1 - elapsedRatio);

    const style = new Style({
      image: new CircleStyle({
        radius: radius,
        stroke: new Stroke({
          color: 'rgba(255, 0, 0, ' + opacity + ')',
          width: 0.25 + opacity,
        }),
      }),
    });

    vectorContext.setStyle(style);
    vectorContext.drawGeometry(flashGeom);
    // tell OpenLayers to continue postrender animation
    // 告诉OpenLayers继续后期渲染动画
    map.render();
  }
}

source.on('addfeature', function (e) {
  flash(e.feature);
});

window.setInterval(addRandomFeature, 1000);

界面布局文件index.html代码如下：

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<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Custom Animation</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>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="https://cdn.jsdelivr.net/npm/elm-pep@1.0.6/dist/elm-pep.js"></script>
    <script type="module" src="main.js"></script>
  </body>
</html>