看过的知识不等于学会。唯有用心总结、系统记录，并通过温故知新反复实践，才能真正掌握一二
作为一名摸爬滚打三年的前端开发，开源社区给了我饭碗，我也将所学的知识体系回馈给大家，助你少走弯路！
OpenLayers、Leaflet 快速入门 ，每周保持更新 2 个案例
Cesium 快速入门，每周保持更新 4 个案例
OpenLayers 综合案例-区域掩膜
Vue 3 + OpenLayers 实现的 WebGIS 应用提供了完整的区域掩膜功能
实现思路
- 主要就是考验 canvas 的使用，核心代码参考openlayers 中区域掩膜的实现
- 在地图容器中添加一个 canvas，设置其在 map 之上；
- 监听 map 的 postrender 事件，每次事件触发重新绘制掩膜；
- 通过 map.getPixelFromCoordinate 实现地理坐标到屏幕坐标的转换；
- 通过 globalCompositeOperation = 'source-out’设置反向裁剪；
MP4效果动画链接地址&JSON数据获取地址
技术栈
该环境下代码即拿即用
Vue 3.5.13+
OpenLayers 10.5.0+
Vite 6.3.5+
<template><div ref="mapContainer" id="map"></div>
</template><script setup>
import { ref, onMounted } from "vue";
import Map from "ol/Map.js";
import XYZ from "ol/source/XYZ.js";
import TileLayer from "ol/layer/Tile.js";
import View from "ol/View.js";
import "ol/ol.css";
import modalData from "./320000_bj.json";const mapContainer = ref(null);
let map = null;
let canvas = null;
let ctx = null;const view = new View({center: [118.7784, 32.0647], // 南京市中心经纬度zoom: 7,projection: "EPSG:4326",
});onMounted(async () => {map = new Map({target: mapContainer.value,layers: [new TileLayer({source: new XYZ({url: "https://webrd04.is.autonavi.com/appmaptile?lang=zh_cn&size=1&scale=1&style=7&x={x}&y={y}&z={z}",}),}),],view,});// 创建canvasconst { offsetWidth, offsetHeight } = map.getViewport();canvas = document.createElement("canvas");canvas.width = offsetWidth;canvas.height = offsetHeight;canvas.style.position = "absolute";canvas.style.top = "0px";canvas.style.left = "0px";canvas.style.zIndex = "1";ctx = canvas.getContext("2d");map.getViewport().appendChild(canvas);// 注册map事件map.on("postrender", () => {addMask();});
});// 添加区域掩膜
const addMask = (params) => {const { fillStyle, strokeStyle, lineWidth } = {fillStyle: "rgba(255,255,255,0.8)",strokeStyle: "#f00",lineWidth: 3,...params,};ctx.clearRect(0, 0, canvas.width, canvas.height);// 获取整个江苏省的所有多边形const jiangsuPolygons = modalData.features[0].geometry.coordinates;// 1. 绘制整个画布为半透明白色ctx.fillStyle = fillStyle;ctx.fillRect(0, 0, canvas.width, canvas.height);// 2. 使用组合模式清除多边形区域ctx.globalCompositeOperation = "destination-out";ctx.fillStyle = "rgba(0,0,0,1)"; // 使用任意颜色，alpha=1确保完全清除// 绘制所有多边形（包括主区域和岛屿）jiangsuPolygons.forEach((polygon) => {const ring = polygon[0]; // 获取多边形外环const coords = ring.map((coord) => map.getPixelFromCoordinate(coord));ctx.beginPath();coords.forEach((coord, index) => {index === 0? ctx.moveTo(coord[0], coord[1]): ctx.lineTo(coord[0], coord[1]);});ctx.closePath();ctx.fill();});// 3. 恢复组合模式并绘制边界ctx.globalCompositeOperation = "source-over";ctx.strokeStyle = strokeStyle;ctx.lineWidth = lineWidth;// 绘制所有多边形的边界jiangsuPolygons.forEach((polygon) => {const ring = polygon[0];const coords = ring.map((coord) => map.getPixelFromCoordinate(coord));ctx.beginPath();coords.forEach((coord, index) => {index === 0? ctx.moveTo(coord[0], coord[1]): ctx.lineTo(coord[0], coord[1]);});ctx.closePath();ctx.stroke();});
};
</script><style scoped>
#map {position: absolute;top: 0;bottom: 0;width: 100vw;height: 100vh;
}
</style>
)
