Icon Sprites with WebGL——WebGL图标精灵

最新推荐文章于 2024-12-11 17:25:26 发布

翻译最新推荐文章于 2024-12-11 17:25:26 发布 · 730 阅读

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本文介绍了一个使用WebGL渲染大量带有不同样式的图标精灵的例子。通过OpenLayers库创建了一个地图应用，展示了如何利用图标精灵提高WebGL性能，并实现动态样式变化。

In this example a sprite image is used for the icon styles. Using a sprite is required to get good performance with WebGL.
在这个例子中，图标精灵用于图标样式。使用精灵需要WebGL获取好的性能。

代码：

<!DOCTYPE html>
<html>
  <head>
    <title>Icon Sprites with WebGL</title>
    <link rel="stylesheet" href="https://openlayers.org/en/v4.2.0/css/ol.css" type="text/css">
    <!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
    <script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script>
    <script src="https://openlayers.org/en/v4.2.0/build/ol.js"></script>
  </head>
  <body>
    <div id="map" class="map"></div>
    <div id="info"> </div>
    <script>
      // 图标信息，存储的都是Icon样式的属性，便于动态赋予不同的样式
      var iconInfo = [{
        offset: [0, 0],
        opacity: 1.0,
        rotateWithView: true,
        rotation: 0.0,
        scale: 1.0,
        size: [55, 55]
      }, {
        offset: [110, 86],
        opacity: 0.75,
        rotateWithView: false,
        rotation: Math.PI / 2.0,
        scale: 1.25,
        size: [55, 55]
      }, {
        offset: [55, 0],
        opacity: 0.5,
        rotateWithView: true,
        rotation: Math.PI / 3.0,
        scale: 1.5,
        size: [55, 86]
      }, {
        offset: [212, 0],
        opacity: 1.0,
        rotateWithView: true,
        rotation: 0.0,
        scale: 1.0,
        size: [44, 44]
      }];

      var i;

      // 获取样式信息的数量
      var iconCount = iconInfo.length;
      // 创建icons数组
      var icons = new Array(iconCount);
      for (i = 0; i < iconCount; ++i) {
        var info = iconInfo[i];
        // 为每一个图标分配Icon样式
        icons[i] = new ol.style.Icon({
          offset: info.offset,
          opacity: info.opacity,
          rotateWithView: info.rotateWithView,
          rotation: info.rotation,
          scale: info.scale,
          size: info.size,
          crossOrigin: 'anonymous',
          src: 'https://openlayers.org/en/v4.2.0/examples/data/Butterfly.png'
        });
      }

      // 要素数量
      var featureCount = 50000;
      // 要素数组
      var features = new Array(featureCount);
      var feature, geometry;
      var e = 25000000;
      // 随机创建50000个点要素并为其分配样式
      for (i = 0; i < featureCount; ++i) {
        // 随机创建点对象
        geometry = new ol.geom.Point(
            [2 * e * Math.random() - e, 2 * e * Math.random() - e]);
        // 新建要素
        feature = new ol.Feature(geometry);
        // 设置样式
        feature.setStyle(
            new ol.style.Style({
              image: icons[i % (iconCount - 1)]
            })
        );
        features[i] = feature;
      }

      // 创建矢量数据源
      var vectorSource = new ol.source.Vector({
        features: features
      });
      // 创建矢量图层
      var vector = new ol.layer.Vector({
        source: vectorSource
      });

      var map = new ol.Map({
        renderer: /** @type {ol.renderer.Type} */ ('webgl'),
        layers: [vector],
        target: document.getElementById('map'),
        view: new ol.View({
          center: [0, 0],
          zoom: 5
        })
      });

      // 创建覆盖要素数组
      var overlayFeatures = [];
      // 复制先前创建的要素并添加到覆盖覆盖数组中
      for (i = 0; i < featureCount; i += 30) {
        // 复制要素
        var clone = features[i].clone();
        // 去掉复制要素的样式
        clone.setStyle(null);
        // 添加到覆盖数组中
        overlayFeatures.push(clone);
      }

      // 矢量图层
      new ol.layer.Vector({
        map: map,
        source: new ol.source.Vector({
          features: overlayFeatures
        }),
        style: new ol.style.Style({
          image: icons[iconCount - 1]
        })
      });

      // 鼠标在地图上单击时显示单击位置有多少多少个要素
      map.on('click', function(evt) {
        var info = document.getElementById('info');
        info.innerHTML =
            'Hold on a second, while I catch those butterflies for you ...';

        window.setTimeout(function() {
          var features = [];
          map.forEachFeatureAtPixel(evt.pixel, function(feature) {
            features.push(feature);
            return false;
          });

          if (features.length === 1) {
            info.innerHTML = 'Got one butterfly';
          } else if (features.length > 1) {
            info.innerHTML = 'Got ' + features.length + ' butterflies';
          } else {
            info.innerHTML = 'Couldn\'t catch a single butterfly';
          }
        }, 1);
      });

      // 鼠标在地图上移动时，如果该位置有要素存在则改变鼠标样式
      map.on('pointermove', function(evt) {
        if (evt.dragging) {
          return;
        }
        var pixel = map.getEventPixel(evt.originalEvent);
        var hit = map.hasFeatureAtPixel(pixel);
        map.getTarget().style.cursor = hit ? 'pointer' : '';
      });
    </script>
  </body>
</html>