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Tile Load Events

tile9 events2 loading7

Example using tile load events.

Image tile sources fire events related to tile loading. You can listen for tileloadstart, tileloadend, and tileloaderror type events to monitor tile loading progress. This example registers listeners for these events and renders a tile loading progress bar at the bottom of the map.

main.js
import 'ol/ol.css';
import Map from 'ol/Map';
import TileLayer from 'ol/layer/Tile';
import View from 'ol/View';
import XYZ from 'ol/source/XYZ';

/**
 * Renders a progress bar.
 * @param {HTMLElement} el The target element.
 * @class
 */
function Progress(el) {
  this.el = el;
  this.loading = 0;
  this.loaded = 0;
}

/**
 * Increment the count of loading tiles.
 */
Progress.prototype.addLoading = function () {
  if (this.loading === 0) {
    this.show();
  }
  ++this.loading;
  this.update();
};

/**
 * Increment the count of loaded tiles.
 */
Progress.prototype.addLoaded = function () {
  const this_ = this;
  setTimeout(function () {
    ++this_.loaded;
    this_.update();
  }, 100);
};

/**
 * Update the progress bar.
 */
Progress.prototype.update = function () {
  const width = ((this.loaded / this.loading) * 100).toFixed(1) + '%';
  this.el.style.width = width;
  if (this.loading === this.loaded) {
    this.loading = 0;
    this.loaded = 0;
    const this_ = this;
    setTimeout(function () {
      this_.hide();
    }, 500);
  }
};

/**
 * Show the progress bar.
 */
Progress.prototype.show = function () {
  this.el.style.visibility = 'visible';
};

/**
 * Hide the progress bar.
 */
Progress.prototype.hide = function () {
  if (this.loading === this.loaded) {
    this.el.style.visibility = 'hidden';
    this.el.style.width = 0;
  }
};

const progress = new Progress(document.getElementById('progress'));

const key = 'get_your_own_D6rA4zTHduk6KOKTXzGB';
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 source = new XYZ({
  attributions: attributions,
  url: 'https://api.maptiler.com/maps/streets/{z}/{x}/{y}.png?key=' + key,
  tileSize: 512,
});

source.on('tileloadstart', function () {
  progress.addLoading();
});

source.on('tileloadend', function () {
  progress.addLoaded();
});
source.on('tileloaderror', function () {
  progress.addLoaded();
});

const map = new Map({
  layers: [new TileLayer({source: source})],
  target: 'map',
  view: new View({
    center: [0, 0],
    zoom: 2,
  }),
});
index.html
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Tile Load Events</title>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="https://unpkg.com/elm-pep"></script>
    <!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
    <script src="https://cdn.polyfill.io/v3/polyfill.min.js?features=fetch,requestAnimationFrame,Element.prototype.classList,URL,TextDecoder,Number.isInteger"></script>
    <style>
      .map {
        width: 100%;
        height:400px;
      }
      .map {
        background: #85ccf9;
      }
      .wrapper {
        position: relative;
      }
      #progress {
        position: absolute;
        bottom: 0;
        left: 0;
        height: 0;
        box-shadow: 0px 0px 1px 2px rgb(255,204,0);
        width: 0;
        transition: width 250ms;
      }
    </style>
  </head>
  <body>
    <div class="wrapper">
      <div id="map" class="map"></div>
      <div id="progress"></div>
    </div>
    <script src="main.js"></script>
  </body>
</html>
package.json
{
  "name": "tile-load-events",
  "dependencies": {
    "ol": "6.9.0"
  },
  "devDependencies": {
    "parcel": "^2.0.0-beta.1"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --public-url . index.html"
  }
}