Polygon Pattern

<!--
  示例：面纹理填充
  要点：Canvas createPattern 生成斜纹图案，作为 ol.style.Fill 的 color 使用
  依赖：OpenLayers 10.3.1 · jsDelivr CDN
-->
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta name="robots" content="noindex,follow">
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>面纹理填充</title>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/ol@10.3.1/ol.css">
<style>
  html,body{height:100%;margin:0}
  body{display:flex;flex-direction:column;overflow:hidden;
       font:13px/1.6 -apple-system,"Segoe UI","PingFang SC",sans-serif}
  .bar{flex:0 0 auto;padding:8px 12px;background:#f6f7f9;border-bottom:1px solid #e3e6ea;
       display:flex;gap:10px;align-items:center;font-size:12px;color:#58606e}
  .bar button{padding:4px 10px;border:1px solid #cfd4dc;border-radius:4px;
              background:#fff;cursor:pointer;font-size:12px}
  .bar button.on{background:#1f5fd0;border-color:#1f5fd0;color:#fff}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <button id="normal" class="on">标准斜纹</button>
  <button id="dense">密集纹理</button>
  <button id="solid">纯色</button>
</div>
<div id="map"></div>
<script src="https://cdn.jsdelivr.net/npm/ol@10.3.1/dist/ol.js"></script>
<script>
(function () {
  'use strict';

  if (typeof ol === 'undefined') {
    document.getElementById('map').innerHTML =
      '<div style="padding:20px;color:#b42318">OpenLayers 加载失败，请检查能否访问 cdn.jsdelivr.net</div>';
    return;
  }

  var fromLonLat = ol.proj.fromLonLat;

  var blocks = [
    [[116.372, 39.900], [116.398, 39.900], [116.398, 39.916], [116.372, 39.916]],
    [[116.404, 39.906], [116.430, 39.906], [116.430, 39.922], [116.404, 39.922]]
  ].map(function (coords) {
    return new ol.Feature({
      geometry: new ol.geom.Polygon([coords.concat([coords[0]]).map(function (p) {
        return fromLonLat(p);
      })])
    });
  });

  var layer = new ol.layer.Vector({
    source: new ol.source.Vector({ features: blocks })
  });

  /* 按间距绘制斜纹并返回可平铺图案 */
  function makePattern(step) {
    var size = step * 2;
    var c = document.createElement('canvas');
    c.width = size;
    c.height = size;
    var ctx = c.getContext('2d');
    ctx.clearRect(0, 0, size, size);
    ctx.strokeStyle = 'rgba(31, 95, 208, 0.85)';
    ctx.lineWidth = 2;
    ctx.beginPath();
    ctx.moveTo(-size, size);
    ctx.lineTo(size, -size);
    ctx.moveTo(0, size);
    ctx.lineTo(size, 0);
    ctx.moveTo(-size, 0);
    ctx.lineTo(0, -size);
    ctx.stroke();
    return ctx.createPattern(c, 'repeat');
  }

  var patternNormal = makePattern(9);
  var patternDense = makePattern(4);

  function styleWith(colorValue) {
    return new ol.style.Style({
      fill: new ol.style.Fill({ color: colorValue }),
      stroke: new ol.style.Stroke({ color: '#1f5fd0', width: 2 })
    });
  }

  function apply(style) {
    layer.setStyle(style);
  }

  apply(styleWith(patternNormal));

  var buttons = {
    normal: patternNormal,
    dense: patternDense,
    solid: 'rgba(31, 95, 208, 0.35)'
  };

  Object.keys(buttons).forEach(function (key) {
    document.getElementById(key).addEventListener('click', function () {
      apply(styleWith(buttons[key]));
      Array.prototype.forEach.call(document.querySelectorAll('.bar button'), function (b) {
        b.classList.remove('on');
      });
      this.classList.add('on');
    });
  });

  new ol.Map({
    target: 'map',
    layers: [new ol.layer.Tile({ source: new ol.source.XYZ({url: 'https://server.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer/tile/{z}/{y}/{x}', attributions: 'Tiles © Esri'}) }), layer],
    view: new ol.View({
      center: fromLonLat([116.401, 39.911]),
      zoom: 13
    }),
    controls: ol.control.defaults.defaults({ attribution: false })
  });
})();
</script>
</body>
</html>