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 ImageTile from 'ol/source/ImageTile.js';
import Map from 'ol/Map.js';
import TileLayer from 'ol/layer/WebGLTile.js';
import View from 'ol/View.js';

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 ImageTile({
    attributions: attributions,
    url: 'https://api.maptiler.com/maps/satellite/{z}/{x}/{y}.jpg?key=' + key,
    tileSize: 512,
    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);
  element.addEventListener('input', function (event) {
    const value = parseFloat(event.target.value);
    document.getElementById(name + '-value').innerText = value.toFixed(2);
    const updates = {};
    updates[name] = value;
    layer.updateStyleVariables(updates);
  });
}

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>WebGL Tile Layer Styles</title>
    <link rel="stylesheet" href="node_modules/ol/ol.css">
    <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 type="module" src="main.js"></script>
  </body>
</html>

package.json

{
  "name": "webgl-tile-style",
  "dependencies": {
    "ol": "10.2.1"
  },
  "devDependencies": {
    "vite": "^3.2.3"
  },
  "scripts": {
    "start": "vite",
    "build": "vite build"
  }
}