#### 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
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,
});
}
}

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

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

``````
##### index.html
``````<!DOCTYPE html>
<html lang="en">
<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/[email protected]/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>
<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": "6.14.1"
},
"devDependencies": {
"parcel": "^2.0.0"
},
"scripts": {
"start": "parcel index.html",
"build": "parcel build --public-url . index.html"
}
}``````