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 coverts a circle into a start using the center and radius provided by the draw interaction.

<!DOCTYPE html>
<html>
  <head>
    <title>Draw Shapes</title>
    <link rel="stylesheet" href="https://openlayers.org/en/v4.6.4/css/ol.css" type="text/css">
    <!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
    <script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script>
    <script src="https://openlayers.org/en/v4.6.4/build/ol.js"></script>
  </head>
  <body>
    <div id="map" class="map"></div>
    <form class="form-inline">
      <label>Shape type &nbsp;</label>
      <select id="type">
        <option value="Square">Square</option>
        <option value="Box">Box</option>
        <option value="Star">Star</option>
        <option value="None">None</option>
      </select>
    </form>
    <script>
      var raster = new ol.layer.Tile({
        source: new ol.source.OSM()
      });

      var source = new ol.source.Vector({wrapX: false});

      var vector = new ol.layer.Vector({
        source: source
      });

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

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

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


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

      addInteraction();
    </script>
  </body>
</html>