矢量标签【译】

原文链接及内容

原文链接：https://openlayers.org/en/latest/examples/vector-labels.html

此示例展示了为文本样式设置多个选项。当选择”Text/Wrap”(例如线要素)时，通过插入字符\n使得标签换行，这将创建多行标签。“Open Sans”web字体将按需加载，以展示动态字体的加载。

main.js代码如下：

import GeoJSON from 'ol/format/GeoJSON.js';
import Map from 'ol/Map.js';
import View from 'ol/View.js';
import {
  Circle as CircleStyle,
  Fill,
  Stroke,
  Style,
  Text,
} from 'ol/style.js';
import {OSM, Vector as VectorSource} from 'ol/source.js';
import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer.js';

let openSansAdded = false;

const myDom = {
  points: {
    text: document.getElementById('points-text'),
    align: document.getElementById('points-align'),
    baseline: document.getElementById('points-baseline'),
    rotation: document.getElementById('points-rotation'),
    font: document.getElementById('points-font'),
    weight: document.getElementById('points-weight'),
    size: document.getElementById('points-size'),
    height: document.getElementById('points-height'),
    offsetX: document.getElementById('points-offset-x'),
    offsetY: document.getElementById('points-offset-y'),
    color: document.getElementById('points-color'),
    outline: document.getElementById('points-outline'),
    outlineWidth: document.getElementById('points-outline-width'),
    maxreso: document.getElementById('points-maxreso'),
  },
  lines: {
    text: document.getElementById('lines-text'),
    align: document.getElementById('lines-align'),
    baseline: document.getElementById('lines-baseline'),
    rotation: document.getElementById('lines-rotation'),
    font: document.getElementById('lines-font'),
    weight: document.getElementById('lines-weight'),
    placement: document.getElementById('lines-placement'),
    maxangle: document.getElementById('lines-maxangle'),
    overflow: document.getElementById('lines-overflow'),
    size: document.getElementById('lines-size'),
    height: document.getElementById('lines-height'),
    offsetX: document.getElementById('lines-offset-x'),
    offsetY: document.getElementById('lines-offset-y'),
    color: document.getElementById('lines-color'),
    outline: document.getElementById('lines-outline'),
    outlineWidth: document.getElementById('lines-outline-width'),
    maxreso: document.getElementById('lines-maxreso'),
  },
  polygons: {
    text: document.getElementById('polygons-text'),
    align: document.getElementById('polygons-align'),
    baseline: document.getElementById('polygons-baseline'),
    rotation: document.getElementById('polygons-rotation'),
    font: document.getElementById('polygons-font'),
    weight: document.getElementById('polygons-weight'),
    placement: document.getElementById('polygons-placement'),
    maxangle: document.getElementById('polygons-maxangle'),
    overflow: document.getElementById('polygons-overflow'),
    size: document.getElementById('polygons-size'),
    height: document.getElementById('polygons-height'),
    offsetX: document.getElementById('polygons-offset-x'),
    offsetY: document.getElementById('polygons-offset-y'),
    color: document.getElementById('polygons-color'),
    outline: document.getElementById('polygons-outline'),
    outlineWidth: document.getElementById('polygons-outline-width'),
    maxreso: document.getElementById('polygons-maxreso'),
  },
};

const getText = function (feature, resolution, dom) {
  const type = dom.text.value;
  const maxResolution = dom.maxreso.value;
  let text = feature.get('name');

  if (resolution > maxResolution) {
    text = '';
  } else if (type == 'hide') {
    text = '';
  } else if (type == 'shorten') {
    text = text.trunc(12);
  } else if (
    type == 'wrap' &&
    (!dom.placement || dom.placement.value != 'line')
  ) {
    text = stringDivider(text, 16, '\n');
  }

  return text;
};

const createTextStyle = function (feature, resolution, dom) {
  const align = dom.align.value;
  const baseline = dom.baseline.value;
  const size = dom.size.value;
  const height = dom.height.value;
  const offsetX = parseInt(dom.offsetX.value, 10);
  const offsetY = parseInt(dom.offsetY.value, 10);
  const weight = dom.weight.value;
  const placement = dom.placement ? dom.placement.value : undefined;
  const maxAngle = dom.maxangle ? parseFloat(dom.maxangle.value) : undefined;
  const overflow = dom.overflow ? dom.overflow.value == 'true' : undefined;
  const rotation = parseFloat(dom.rotation.value);
  if (dom.font.value == "'Open Sans'" && !openSansAdded) {
    const openSans = document.createElement('link');
    openSans.href = 'https://fonts.googleapis.com/css?family=Open+Sans';
    openSans.rel = 'stylesheet';
    document.head.appendChild(openSans);
    openSansAdded = true;
  }
  const font = weight + ' ' + size + '/' + height + ' ' + dom.font.value;
  const fillColor = dom.color.value;
  const outlineColor = dom.outline.value;
  const outlineWidth = parseInt(dom.outlineWidth.value, 10);

  return new Text({
    textAlign: align == '' ? undefined : align,
    textBaseline: baseline,
    font: font,
    text: getText(feature, resolution, dom),
    fill: new Fill({color: fillColor}),
    stroke: new Stroke({color: outlineColor, width: outlineWidth}),
    offsetX: offsetX,
    offsetY: offsetY,
    placement: placement,
    maxAngle: maxAngle,
    overflow: overflow,
    rotation: rotation,
  });
};

// Polygons
function polygonStyleFunction(feature, resolution) {
  return new Style({
    stroke: new Stroke({
      color: 'blue',
      width: 1,
    }),
    fill: new Fill({
      color: 'rgba(0, 0, 255, 0.1)',
    }),
    text: createTextStyle(feature, resolution, myDom.polygons),
  });
}

const vectorPolygons = new VectorLayer({
  source: new VectorSource({
    url: 'data/geojson/polygon-samples.geojson',
    format: new GeoJSON(),
  }),
  style: polygonStyleFunction,
});

// Lines
function lineStyleFunction(feature, resolution) {
  return new Style({
    stroke: new Stroke({
      color: 'green',
      width: 2,
    }),
    text: createTextStyle(feature, resolution, myDom.lines),
  });
}

const vectorLines = new VectorLayer({
  source: new VectorSource({
    url: 'data/geojson/line-samples.geojson',
    format: new GeoJSON(),
  }),
  style: lineStyleFunction,
});

// Points
function pointStyleFunction(feature, resolution) {
  return new Style({
    image: new CircleStyle({
      radius: 10,
      fill: new Fill({color: 'rgba(255, 0, 0, 0.1)'}),
      stroke: new Stroke({color: 'red', width: 1}),
    }),
    text: createTextStyle(feature, resolution, myDom.points),
  });
}

const vectorPoints = new VectorLayer({
  source: new VectorSource({
    url: 'data/geojson/point-samples.geojson',
    format: new GeoJSON(),
  }),
  style: pointStyleFunction,
});

const map = new Map({
  layers: [
    new TileLayer({
      source: new OSM(),
    }),
    vectorPolygons,
    vectorLines,
    vectorPoints,
  ],
  target: 'map',
  view: new View({
    center: [-8161939, 6095025],
    zoom: 8,
  }),
});

document
  .getElementById('refresh-points')
  .addEventListener('click', function () {
    vectorPoints.setStyle(pointStyleFunction);
  });

document.getElementById('refresh-lines').addEventListener('click', function () {
  vectorLines.setStyle(lineStyleFunction);
});

document
  .getElementById('refresh-polygons')
  .addEventListener('click', function () {
    vectorPolygons.setStyle(polygonStyleFunction);
  });

/**
 * @param {number} n The max number of characters to keep.
 * @return {string} Truncated string.
 */
String.prototype.trunc =
  String.prototype.trunc ||
  function (n) {
    return this.length > n ? this.substr(0, n - 1) + '...' : this.substr(0);
  };

// https://stackoverflow.com/questions/14484787/wrap-text-in-javascript
function stringDivider(str, width, spaceReplacer) {
  if (str.length > width) {
    let p = width;
    while (p > 0 && str[p] != ' ' && str[p] != '-') {
      p--;
    }
    if (p > 0) {
      let left;
      if (str.substring(p, p + 1) == '-') {
        left = str.substring(0, p + 1);
      } else {
        left = str.substring(0, p);
      }
      const right = str.substring(p + 1);
      return left + spaceReplacer + stringDivider(right, width, spaceReplacer);
    }
  }
  return str;
}

界面布局文件index.html代码如下：

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Vector Labels</title>
    <link rel="stylesheet" href="node_modules/ol/ol.css">
    <style>
      .map {
        width: 100%;
        height: 400px;
      }
      .edit-form {
        display: inline-block;
        margin: 5px;
        padding: 10px;
        border: 1px solid black;
        white-space: nowrap;
      }

      .edit-form h2 {
        font-size: 1.5em;
      }

      .edit-form input[type="button"] {
        float: right;
      }

      .edit-form-elem label {
        display: inline-block;
        width: 85px;
      }

      .edit-form-elem input[type="text"],
      .edit-form-elem select {
        width: 130px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>

    <div class="edit-form">
      <input id="refresh-points" type="button" value="Refresh" />
      <h2>Points</h2>
      <div class="edit-form-elem">
        <label for="points-text">Text: </label>
        <select id="points-text">
          <option value="hide">Hide</option>
          <option value="normal">Normal</option>
          <option value="shorten" selected="selected">Shorten</option>
          <option value="wrap">Wrap</option>
        </select>
        <br />
        <label for="points-maxreso" title="Max Resolution Denominator">MaxReso.: </label>
        <select id="points-maxreso">
          <option value="38400">38,400</option>
          <option value="19200">19,200</option>
          <option value="9600">9,600</option>
          <option value="4800">4,800</option>
          <option value="2400">2,400</option>
          <option value="1200" selected="selected">1,200</option>
          <option value="600">600</option>
          <option value="300">300</option>
          <option value="150">150</option>
          <option value="75">75</option>
          <option value="32">32</option>
          <option value="16">16</option>
          <option value="8">8</option>
        </select>
        <br />
        <label for="points-align">Align: </label>
        <select id="points-align">
          <option value="center" selected="selected">Center</option>
          <option value="end">End</option>
          <option value="left">Left</option>
          <option value="right">Right</option>
          <option value="start">Start</option>
        </select>
        <br />
        <label for="points-baseline">Baseline: </label>
        <select id="points-baseline">
          <option value="alphabetic">Alphabetic</option>
          <option value="bottom">Bottom</option>
          <option value="hanging">Hanging</option>
          <option value="ideographic">Ideographic</option>
          <option value="middle" selected="selected">Middle</option>
          <option value="top">Top</option>
        </select>
        <br />
        <label for="points-rotation">Rotation: </label>
        <select id="points-rotation">
          <option value="0">0°</option>
          <option value="0.785398164">45°</option>
          <option value="1.570796327">90°</option>
        </select>
        <br />
        <label for="points-font">Font: </label>
        <select id="points-font">
          <option value="Arial" selected="selected">Arial</option>
          <option value="'Courier New'">Courier New</option>
          <option value="'Open Sans'">Open Sans</option>
          <option value="Verdana">Verdana</option>
        </select>
        <br />
        <label for="points-weight">Weight: </label>
        <select id="points-weight">
          <option value="bold">Bold</option>
          <option value="normal" selected="selected">Normal</option>
        </select>
        <br />
        <label for="points-placement">Placement: </label>
        <select disabled id="points-placement">
          <option value="line">Line</option>
          <option value="point" selected="selected">Point</option>
        </select>
        <br />
        <label for="points-maxangle">Max Angle: </label>
        <select disabled id="points-maxangle">
          <option value="0.7853981633974483" selected="selected">45°</option>
          <option value="2.0943951023931953">120°</option>
          <option value="6.283185307179586">360°</option>
        </select>
        <br />
        <label for="points-overflow">Exceed Len: </label>
        <select disabled id="points-overflow">
          <option value="true">True</option>
          <option value="false" selected="selected">False</option>
        </select>
        <br />
        <label for="points-size">Size: </label>
        <input type="text" value="12px" id="points-size" />
        <br />
        <label for="points-height">Line height: </label>
        <input type="text" value="1" id="points-height" />
        <br />
        <label for="points-offset-x">Offset X: </label>
        <input type="text" value="0" id="points-offset-x" />
        <br />
        <label for="points-offset-y">Offset Y: </label>
        <input type="text" value="0" id="points-offset-y" />
        <br />
        <label for="points-color">Color: </label>
        <input type="text" value="#aa3300" id="points-color" />
        <br />
        <label for="points-outline" title="Outline Color">O. Color: </label>
        <input type="text" value="#ffffff" id="points-outline" />
        <br />
        <label for="points-outline-width" title="Outline Width">O. Width: </label>
        <input type="text" value="3" id="points-outline-width" />
      </div>
    </div>

    <div class="edit-form">
      <input id="refresh-lines" type="button" value="Refresh" />
      <h2>Lines</h2>
      <div class="edit-form-elem">
        <label for="lines-text">Text: </label>
        <select id="lines-text">
          <option value="hide">Hide</option>
          <option value="normal">Normal</option>
          <option value="shorten">Shorten</option>
          <option value="wrap" selected="selected">Wrap</option>
        </select>
        <br />
        <label for="lines-maxreso" title="Max Resolution Denominator">MaxReso.: </label>
        <select id="lines-maxreso">
          <option value="38400">38,400</option>
          <option value="19200">19,200</option>
          <option value="9600">9,600</option>
          <option value="4800">4,800</option>
          <option value="2400">2,400</option>
          <option value="1200" selected="selected">1,200</option>
          <option value="600">600</option>
          <option value="300">300</option>
          <option value="150">150</option>
          <option value="75">75</option>
          <option value="32">32</option>
          <option value="16">16</option>
          <option value="8">8</option>
        </select>
        <br />
        <label for="lines-align">Align: </label>
        <select id="lines-align">
          <option value="" selected="selected"></option>
          <option value="center">Center</option>
          <option value="end">End</option>
          <option value="left">Left</option>
          <option value="right">Right</option>
          <option value="start">Start</option>
        </select>
        <br />
        <label for="lines-baseline">Baseline: </label>
        <select id="lines-baseline">
          <option value="alphabetic">Alphabetic</option>
          <option value="bottom">Bottom</option>
          <option value="hanging">Hanging</option>
          <option value="ideographic">Ideographic</option>
          <option value="middle" selected="selected">Middle</option>
          <option value="top">Top</option>
        </select>
        <br />
        <label for="lines-rotation">Rotation: </label>
        <select id="lines-rotation">
          <option value="0">0°</option>
          <option value="0.785398164">45°</option>
          <option value="1.570796327">90°</option>
        </select>
        <br />
        <label for="lines-font">Font: </label>
        <select id="lines-font">
          <option value="Arial">Arial</option>
          <option value="'Courier New'" selected="selected">Courier New</option>
          <option value="'Open Sans'">Open Sans</option>
          <option value="Verdana">Verdana</option>
        </select>
        <br />
        <label for="lines-weight">Weight: </label>
        <select id="lines-weight">
          <option value="bold" selected="selected">Bold</option>
          <option value="normal">Normal</option>
        </select>
        <br />
        <label for="lines-placement">Placement: </label>
        <select id="lines-placement">
          <option value="line">Line</option>
          <option value="point" selected="selected">Point</option>
        </select>
        <br />
        <label for="lines-maxangle">Max Angle: </label>
        <select id="lines-maxangle">
          <option value="0.7853981633974483" selected="selected">45°</option>
          <option value="2.0943951023931953">120°</option>
          <option value="6.283185307179586">360°</option>
        </select>
        <br />
        <label for="lines-overflow">Exceed Len: </label>
        <select id="lines-overflow">
          <option value="true">True</option>
          <option value="false" selected="selected">False</option>
        </select>
        <br />
        <label for="lines-size">Size: </label>
        <input type="text" value="12px" id="lines-size" />
        <br />
        <label for="lines-height">Line height: </label>
        <input type="text" value="1.2" id="lines-height" />
        <br />
        <label for="lines-offset-x">Offset X: </label>
        <input type="text" value="0" id="lines-offset-x" />
        <br />
        <label for="lines-offset-y">Offset Y: </label>
        <input type="text" value="0" id="lines-offset-y" />
        <br />
        <label for="lines-color">Color: </label>
        <input type="text" value="green" id="lines-color" />
        <br />
        <label for="lines-outline" title="Outline Color">O. Color: </label>
        <input type="text" value="#ffffff" id="lines-outline" />
        <br />
        <label for="lines-outline-width" title="Outline Width">O. Width: </label>
        <input type="text" value="3" id="lines-outline-width" />
      </div>
    </div>

    <div class="edit-form">
      <input id="refresh-polygons" type="button" value="Refresh" />
      <h2>Polygons</h2>
      <div class="edit-form-elem">
        <label for="polygons-text">Text: </label>
        <select id="polygons-text">
          <option value="hide">Hide</option>
          <option value="normal" selected="selected">Normal</option>
          <option value="shorten">Shorten</option>
          <option value="wrap">Wrap</option>
        </select>
        <br />
        <label for="polygons-maxreso" title="Max Resolution Denominator">MaxReso.: </label>
        <select id="polygons-maxreso">
          <option value="38400">38,400</option>
          <option value="19200">19,200</option>
          <option value="9600">9,600</option>
          <option value="4800">4,800</option>
          <option value="2400">2,400</option>
          <option value="1200" selected="selected">1,200</option>
          <option value="600">600</option>
          <option value="300">300</option>
          <option value="150">150</option>
          <option value="75">75</option>
          <option value="32">32</option>
          <option value="16">16</option>
          <option value="8">8</option>
        </select>
        <br />
        <label for="polygons-align">Align: </label>
        <select id="polygons-align">
          <option value="" selected="selected"></option>
          <option value="center">Center</option>
          <option value="end">End</option>
          <option value="left">Left</option>
          <option value="right">Right</option>
          <option value="start">Start</option>
        </select>
        <br />
        <label for="polygons-baseline">Baseline: </label>
        <select id="polygons-baseline">
          <option value="alphabetic">Alphabetic</option>
          <option value="bottom">Bottom</option>
          <option value="hanging">Hanging</option>
          <option value="ideographic">Ideographic</option>
          <option value="middle" selected="selected">Middle</option>
          <option value="top">Top</option>
        </select>
        <br />
        <label for="polygons-rotation">Rotation: </label>
        <select id="polygons-rotation">
          <option value="0">0°</option>
          <option value="0.785398164">45°</option>
          <option value="1.570796327">90°</option>
        </select>
        <br />
        <label for="polygons-font">Font: </label>
        <select id="polygons-font">
          <option value="Arial">Arial</option>
          <option value="'Courier New'">Courier New</option>
          <option value="'Open Sans'">Open Sans</option>
          <option value="Verdana" selected="selected">Verdana</option>
        </select>
        <br />
        <label for="polygons-weight">Weight: </label>
        <select id="polygons-weight">
          <option value="bold" selected="selected">Bold</option>
          <option value="normal">Normal</option>
        </select>
        <br />
        <label for="polygons-placement">Placement: </label>
        <select id="polygons-placement">
          <option value="line">Line</option>
          <option value="point" selected="selected">Point</option>
        </select>
        <br />
        <label for="polygons-maxangle">Max Angle: </label>
        <select id="polygons-maxangle">
          <option value="0.7853981633974483" selected="selected">45°</option>
          <option value="2.0943951023931953">120°</option>
          <option value="6.283185307179586">360°</option>
        </select>
        <br />
        <label for="polygons-overflow">Exceed Len: </label>
        <select id="polygons-overflow">
          <option value="true">True</option>
          <option value="false" selected="selected">False</option>
        </select>
        <br />
        <label for="polygons-size">Size: </label>
        <input type="text" value="10px" id="polygons-size" />
        <br />
        <label for="polygons-height">Line height: </label>
        <input type="text" value="1" id="polygons-height" />
        <br />
        <label for="polygons-offset-x">Offset X: </label>
        <input type="text" value="0" id="polygons-offset-x" />
        <br />
        <label for="polygons-offset-y">Offset Y: </label>
        <input type="text" value="0" id="polygons-offset-y" />
        <br />
        <label for="polygons-color">Color: </label>
        <input type="text" value="blue" id="polygons-color" />
        <br />
        <label for="polygons-outline" title="Outline Color">O. Color: </label>
        <input type="text" value="#ffffff" id="polygons-outline" />
        <br />
        <label for="polygons-outline-width" title="Outline Width">O. Width: </label>
        <input type="text" value="3" id="polygons-outline-width" />
      </div>
    </div>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="https://cdn.jsdelivr.net/npm/elm-pep@1.0.6/dist/elm-pep.js"></script>
    <script type="module" src="main.js"></script>
  </body>
</html>