Draw Shapes

Using the ol/interaction/Draw to create regular shapes

This demonstrates the use of the geometryFunction option for the ol/interaction/Draw. Select a shape type from the dropdown above to start drawing. To activate freehand drawing, hold the Shift key. Square drawing is achieved by using type: 'Circle' type with a geometryFunction that creates a 4-sided regular polygon instead of a circle. Box drawing uses type: 'Circle' with a geometryFunction that creates a box-shaped polygon instead of a circle. Star drawing uses a custom geometry function that converts a circle into a star using the center and radius provided by the draw interaction.

main.js

import 'ol/ol.css';
import Draw, {
  createBox,
  createRegularPolygon,
} from 'ol/interaction/Draw';
import Map from 'ol/Map';
import Polygon from 'ol/geom/Polygon';
import View from 'ol/View';
import {OSM, Vector as VectorSource} from 'ol/source';
import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer';

const raster = new TileLayer({
  source: new OSM(),
});

const source = new VectorSource({wrapX: false});

const vector = new VectorLayer({
  source: source,
});

const map = new Map({
  layers: [raster, vector],
  target: 'map',
  view: new View({
    center: [-11000000, 4600000],
    zoom: 4,
  }),
});

const typeSelect = document.getElementById('type');

let draw; // global so we can remove it later
function addInteraction() {
  let value = typeSelect.value;
  if (value !== 'None') {
    let geometryFunction;
    if (value === 'Square') {
      value = 'Circle';
      geometryFunction = createRegularPolygon(4);
    } else if (value === 'Box') {
      value = 'Circle';
      geometryFunction = createBox();
    } else if (value === 'Star') {
      value = 'Circle';
      geometryFunction = function (coordinates, geometry) {
        const center = coordinates[0];
        const last = coordinates[coordinates.length - 1];
        const dx = center[0] - last[0];
        const dy = center[1] - last[1];
        const radius = Math.sqrt(dx * dx + dy * dy);
        const rotation = Math.atan2(dy, dx);
        const newCoordinates = [];
        const numPoints = 12;
        for (let i = 0; i < numPoints; ++i) {
          const angle = rotation + (i * 2 * Math.PI) / numPoints;
          const fraction = i % 2 === 0 ? 1 : 0.5;
          const offsetX = radius * fraction * Math.cos(angle);
          const offsetY = radius * fraction * Math.sin(angle);
          newCoordinates.push([center[0] + offsetX, center[1] + offsetY]);
        }
        newCoordinates.push(newCoordinates[0].slice());
        if (!geometry) {
          geometry = new Polygon([newCoordinates]);
        } else {
          geometry.setCoordinates([newCoordinates]);
        }
        return geometry;
      };
    }
    draw = new Draw({
      source: source,
      type: value,
      geometryFunction: geometryFunction,
    });
    map.addInteraction(draw);
  }
}

/**
 * Handle change event.
 */
typeSelect.onchange = function () {
  map.removeInteraction(draw);
  addInteraction();
};

document.getElementById('undo').addEventListener('click', function () {
  draw.removeLastPoint();
});

addInteraction();

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Draw Shapes</title>
    <!-- Pointer events polyfill for old browsers, see https://caniuse.com/#feat=pointer -->
    <script src="https://unpkg.com/elm-pep@1.0.6/dist/elm-pep.js"></script>
    <!-- The lines below are only needed for old environments like Internet Explorer and Android 4.x -->
    <script src="https://cdn.polyfill.io/v3/polyfill.min.js?features=fetch,requestAnimationFrame,Element.prototype.classList,TextDecoder"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/core-js/3.18.3/minified.js"></script>
    <style>
      .map {
        width: 100%;
        height:400px;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <form class="form-inline">
      <label for="type">Shape type: &nbsp;</label>
      <select class="form-control mr-2 mb-2 mt-2" id="type">
        <option value="Circle">Circle</option>
        <option value="Square">Square</option>
        <option value="Box">Box</option>
        <option value="Star">Star</option>
        <option value="None">None</option>
      </select>
      <input class="form-control mr-2 mb-2 mt-2" type="button" value="Undo" id="undo">
    </form>
    <script src="main.js"></script>
  </body>
</html>

package.json

{
  "name": "draw-shapes",
  "dependencies": {
    "ol": "6.13.1-dev"
  },
  "devDependencies": {
    "parcel": "^2.0.0"
  },
  "scripts": {
    "start": "parcel index.html",
    "build": "parcel build --public-url . index.html"
  }
}