详解cesium实现大批量POI点位聚合渲染优化方案

function getScreenSpacePositions(
  collection,
  points,
  scene,
  occluder,
  entityCluster
) {
  if (!defined(collection)) {
    return;
  }
  const length = collection.length;
  for (let i = 0; i < length; ++i) {
    const item = collection.get(i);
    item.clusterShow = false;
    if (
      !item.show ||
      (entityCluster._scene.mode === SceneMode.SCENE3D &&
        !occluder.isPointVisible(item.position))
    ) {
      continue;
    }
    // const canClusterLabels =
    //   entityCluster._clusterLabels && defined(item._labelCollection);
    // const canClusterBillboards =
    //   entityCluster._clusterBillboards && defined(item.id._billboard);
    // const canClusterPoints =
    //   entityCluster._clusterPoints && defined(item.id._point);
    // if (canClusterLabels && (canClusterPoints || canClusterBillboards)) {
    //   continue;
    // }
    const coord = item.computeScreenSpacePosition(scene);
    if (!defined(coord)) {
      continue;
    }
    points.push({
      index: i,
      collection: collection,
      clustered: false,
      coord: coord,
    });
  }
}

import PrimitiveCluster from "@/utils/cesiumCtrl/primitiveCluster";
// 初始化标签实例
const billboardsCollectionCombine = new Cesium.BillboardCollection();
// 初始化实体
const primitives = viewer.scene.primitives.add(
  new Cesium.PrimitiveCollection()
);
getGeojson("/json/schools.geojson").then(({ res }) => {
    // 先获取点位数据
    console.log(res);
    const { features } = res;
    formatClusterPoint(features);
  });
// 整理聚合数据
const formatClusterPoint = (features) => {
  var scene = viewer.scene;
  var primitivecluster = new PrimitiveCluster();
  //与entitycluster相同设置其是否聚合 以及最大最小值
  primitivecluster.enabled = true;
  primitivecluster.pixelRange = 60;
  primitivecluster.minimumClusterSize = 2;
  // primitivecluster._pointCollection = pointCollection;
  // primitivecluster._labelCollection = labelCollection;
  for (let i = 0; i < features.length; i++) {
    const feature = features[i];
    const coordinates = feature.geometry.coordinates;
    const position = Cesium.Cartesian3.fromDegrees(
      coordinates[0],
      coordinates[1]
    );
    // 带图片的点
    billboardsCollectionCombine.add({
      image: "/images/mark-icon.png",
      width: 32,
      height: 32,
      position,
    });
  }
  // 将数据传给primitivecluster的标签属性
  primitivecluster._billboardCollection = billboardsCollectionCombine;
  // 初始化
  primitivecluster._initialize(scene);
  // 将标签数据添加到实体中
  primitives.add(primitivecluster);
  // 监听相机缩放
  primitivecluster.clusterEvent.addEventListener(
    (clusteredEntities, cluster) => {
      // 关闭自带的显示聚合数量的标签
      cluster.label.show = false;
      cluster.billboard.show = true;
      cluster.billboard.verticalOrigin = Cesium.VerticalOrigin.BOTTOM;
      // 根据聚合数量的多少设置不同层级的图片以及大小
      cluster.billboard.image = combineIconAndLabel(
        "/images/school-icon.png",
        clusteredEntities.length,
        64
      );
      // cluster.billboard.image = "/images/school-icon.png";
      cluster.billboard._imageHeight = 60;
      cluster.billboard._imageWidth = 60;
      cluster.billboard._dirty = false;
      cluster.billboard.width = 40;
      cluster.billboard.height = 40;
    }
  );
  return primitivecluster;
};
/**
 * @description: 将图片和文字合成新图标使用（参考Cesium源码）
 * @param {*} url：图片地址
 * @param {*} label：文字
 * @param {*} size：画布大小
 * @return {*} 返回canvas
 */
function combineIconAndLabel(url, label, size) {
  // 创建画布对象
  let canvas = document.createElement("canvas");
  canvas.width = size;
  canvas.height = size;
  let ctx = canvas.getContext("2d");
  let promise = new Cesium.Resource.fetchImage(url).then((image) => {
    // 异常判断
    try {
      ctx.drawImage(image, 0, 0);
    } catch (e) {
      console.log(e);
    }
    // 渲染字体
    // font属性设置顺序：font-style, font-variant, font-weight, font-size, line-height, font-family
    ctx.fillStyle = Cesium.Color.BLACK.toCssColorString();
    ctx.font = "bold 20px Microsoft YaHei";
    ctx.textAlign = "center";
    ctx.textBaseline = "middle";
    ctx.fillText(label, size / 2, size / 2);
    return canvas;
  });
  return promise;
}