Layer Swipe

main.js

import ImageTile from 'ol/source/ImageTile.js';
import Map from 'ol/Map.js';
import OSM from 'ol/source/OSM.js';
import TileLayer from 'ol/layer/Tile.js';
import View from 'ol/View.js';
import {getRenderPixel} from 'ol/render.js';

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

const key = 'Get your own API key at https://www.maptiler.com/cloud/';
const attributions =
  '<a href="https://www.maptiler.com/copyright/" target="_blank">&copy; MapTiler</a> ' +
  '<a href="https://www.openstreetmap.org/copyright" target="_blank">&copy; OpenStreetMap contributors</a>';

const aerial = new TileLayer({
  source: new ImageTile({
    attributions: attributions,
    url: 'https://api.maptiler.com/maps/satellite/{z}/{x}/{y}.jpg?key=' + key,
    tileSize: 512,
    maxZoom: 20,
  }),
});

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

const swipe = document.getElementById('swipe');

aerial.on('prerender', function (event) {
  const ctx = event.context;
  const mapSize = map.getSize();
  const width = mapSize[0] * (swipe.value / 100);
  const tl = getRenderPixel(event, [width, 0]);
  const tr = getRenderPixel(event, [mapSize[0], 0]);
  const bl = getRenderPixel(event, [width, mapSize[1]]);
  const br = getRenderPixel(event, mapSize);

  ctx.save();
  ctx.beginPath();
  ctx.moveTo(tl[0], tl[1]);
  ctx.lineTo(bl[0], bl[1]);
  ctx.lineTo(br[0], br[1]);
  ctx.lineTo(tr[0], tr[1]);
  ctx.closePath();
  ctx.clip();
});

aerial.on('postrender', function (event) {
  const ctx = event.context;
  ctx.restore();
});

swipe.addEventListener('input', function () {
  map.render();
});

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Layer Swipe</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>
    <input id="swipe" type="range" style="width: 100%">

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

package.json

{
  "name": "layer-swipe",
  "dependencies": {
    "ol": "10.2.1"
  },
  "devDependencies": {
    "vite": "^3.2.3"
  },
  "scripts": {
    "start": "vite",
    "build": "vite build"
  }
}