数据瓦片

从零生成瓦片数据.

本示例演示从零开始生成 RGBA 瓦片数据.

main.js

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

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>
    <link rel="stylesheet" href="node_modules/ol/ol.css">
    <style>
      .map {
        width: 100%;
        height: 400px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="./resources/elm-pep.js"></script>
    <script type="module" src="main.js"></script>
  </body>
</html>

package.json

{
  "name": "data-tiles",
  "dependencies": {
    "ol": "7.3.0"
  },
  "devDependencies": {
    "vite": "^3.2.3"
  },
  "scripts": {
    "start": "vite",
    "build": "vite build"
  }
}