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Layer Clipping

Layer clipping example

Layer clipping example

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index.html<!DOCTYPE html>
<html lang="en">
  <head>
    <title>Layer Clipping</title>
    <!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
    <script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script>
    <style>
      .map {
        width: 100%;
        height:400px;
      }
      #map {
        background: transparent;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <script src="index.js"></script>
  </body>
</html>
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index.jsimport 'ol/ol.css';
import Map from 'ol/Map';
import View from 'ol/View';
import TileLayer from 'ol/layer/Tile';
import OSM from 'ol/source/OSM';

var osm = new TileLayer({
  source: new OSM()
});

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

osm.on('prerender', function(event) {
  var ctx = event.context;
  ctx.save();
  var pixelRatio = event.frameState.pixelRatio;
  var size = map.getSize();
  ctx.translate(size[0] / 2 * pixelRatio, size[1] / 2 * pixelRatio);
  ctx.scale(3 * pixelRatio, 3 * pixelRatio);
  ctx.translate(-75, -80);
  ctx.beginPath();
  ctx.moveTo(75, 40);
  ctx.bezierCurveTo(75, 37, 70, 25, 50, 25);
  ctx.bezierCurveTo(20, 25, 20, 62.5, 20, 62.5);
  ctx.bezierCurveTo(20, 80, 40, 102, 75, 120);
  ctx.bezierCurveTo(110, 102, 130, 80, 130, 62.5);
  ctx.bezierCurveTo(130, 62.5, 130, 25, 100, 25);
  ctx.bezierCurveTo(85, 25, 75, 37, 75, 40);
  ctx.clip();
  ctx.translate(75, 80);
  ctx.scale(1 / 3 / pixelRatio, 1 / 3 / pixelRatio);
  ctx.translate(-size[0] / 2 * pixelRatio, -size[1] / 2 * pixelRatio);
});

osm.on('postrender', function(event) {
  var ctx = event.context;
  ctx.restore();
});
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package.json{
  "name": "layer-clipping",
  "dependencies": {
    "ol": "6.1.1"
  },
  "devDependencies": {
    "parcel": "1.11.0"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --experimental-scope-hoisting --public-url . index.html"
  }
}