WebGL Tile Layer Styles

exposure
contrast
saturation

Styling raster tiles with WebGL.

The style property of a WebGL tile layer can be used to adjust properties like exposure, contrast, and saturation. Typically those values would be set to numeric constants to apply a filter to imagery. In this example, the style properties are set to variables that can be updated based on application state. Adjusting the sliders results in a call to layer.updateStyleVariables() to use new values for the associated style properties.

main.js

import 'ol/ol.css';
import Map from 'ol/Map';
import TileLayer from 'ol/layer/WebGLTile';
import View from 'ol/View';
import XYZ from 'ol/source/XYZ';

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 variables = {
  exposure: 0,
  contrast: 0,
  saturation: 0,
};

const layer = new TileLayer({
  style: {
    exposure: ['var', 'exposure'],
    contrast: ['var', 'contrast'],
    saturation: ['var', 'saturation'],
    variables: variables,
  },
  source: new XYZ({
    attributions: attributions,
    url: 'https://api.maptiler.com/tiles/satellite/{z}/{x}/{y}.jpg?key=' + key,
    maxZoom: 20,
  }),
});

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

let variable;
for (variable in variables) {
  const name = variable;
  const element = document.getElementById(name);
  const value = variables[name];
  element.value = value.toString();
  document.getElementById(name + '-value').innerText = value.toFixed(2);
  const listener = function (event) {
    const value = parseFloat(event.target.value);
    document.getElementById(name + '-value').innerText = value.toFixed(2);
    const updates = {};
    updates[name] = value;
    layer.updateStyleVariables(updates);
  };
  element.addEventListener('input', listener);
  element.addEventListener('change', listener);
}

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>WebGL Tile Layer Styles</title>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="https://unpkg.com/elm-pep@1.0.6/dist/elm-pep.js"></script>
    <!-- The lines below are 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,TextDecoder"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/core-js/3.18.3/minified.js"></script>
    <style>
      .map {
        width: 100%;
        height:400px;
      }
      #controls {
        display: flex;
        justify-content: space-around;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <div id="controls">
      <label>
        <input id="exposure" type="range" min="-0.5" max="0.5" step="0.01">
        <br>exposure <span id="exposure-value"></span>
      </label>
      <label>
        <input id="contrast" type="range" min="-0.5" max="0.5" step="0.01">
        <br>contrast <span id="contrast-value"></span>
      </label>
      <label>
        <input id="saturation" type="range" min="-0.5" max="0.5" step="0.01">
        <br>saturation <span id="saturation-value"></span>
      </label>
    </div>    <script src="main.js"></script>
  </body>
</html>

package.json

{
  "name": "webgl-tile-style",
  "dependencies": {
    "ol": "6.13.1-dev"
  },
  "devDependencies": {
    "parcel": "^2.0.0"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --public-url . index.html"
  }
}