Data Tiles

Generating tile data from scratch.

This example generates RGBA tile data from scratch.

main.js

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

const size = 256;

const canvas = document.createElement('canvas');
canvas.width = size;
canvas.height = size;

const context = canvas.getContext('2d');
context.strokeStyle = 'white';
context.textAlign = 'center';
context.font = '24px sans-serif';
const lineHeight = 30;

const map = new Map({
  target: 'map',
  layers: [
    new TileLayer({
      source: new DataTile({
        loader: function (z, x, y) {
          const half = size / 2;
          context.clearRect(0, 0, size, size);
          context.fillStyle = 'rgba(100, 100, 100, 0.5)';
          context.fillRect(0, 0, size, size);
          context.fillStyle = 'black';
          context.fillText(`z: ${z}`, half, half - lineHeight);
          context.fillText(`x: ${x}`, half, half);
          context.fillText(`y: ${y}`, half, half + lineHeight);
          context.strokeRect(0, 0, size, size);
          const data = context.getImageData(0, 0, size, size).data;
          // converting to Uint8Array for increased browser compatibility
          return new Uint8Array(data.buffer);
        },
        // disable opacity transition to avoid overlapping labels during tile loading
        transition: 0,
      }),
    }),
  ],
  view: new View({
    center: [0, 0],
    zoom: 0,
  }),
});

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Data Tiles</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;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <script src="main.js"></script>
  </body>
</html>

package.json

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