Add functions to create regular polygons

src/ol/geom/polygon.js

@@ -2,6 +2,7 @@ goog.provide('ol.geom.Polygon');
 
 goog.require('goog.array');
 goog.require('goog.asserts');
+goog.require('goog.math');
 goog.require('ol.extent');
 goog.require('ol.geom.GeometryLayout');
 goog.require('ol.geom.GeometryType');
@@ -422,3 +423,52 @@ ol.geom.Polygon.fromExtent = function(extent) {
       ol.geom.GeometryLayout.XY, flatCoordinates, [flatCoordinates.length]);
   return polygon;
 };
+
+
+/**
+ * Create a regular polygon from a circle.
+ * @param {ol.geom.Circle} circle Circle geometry.
+ * @param {number=} opt_sides Number of sides of the polygon. Default is 32.
+ * @param {number=} opt_angle Start angle for the first vertex of the polygon in
+ *     radians. Default is 0.
+ * @return {ol.geom.Polygon} Polygon geometry.
+ */
+ol.geom.Polygon.fromCircle = function(circle, opt_sides, opt_angle) {
+  var sides = goog.isDef(opt_sides) ? opt_sides : 32;
+  var stride = circle.getStride();
+  var layout = circle.getLayout();
+  var polygon = new ol.geom.Polygon(null, layout);
+  var flatCoordinates = goog.array.repeat(0, stride * (sides + 1));
+  var ends = [flatCoordinates.length];
+  polygon.setFlatCoordinates(layout, flatCoordinates, ends);
+  ol.geom.Polygon.makeRegular(
+      polygon, circle.getCenter(), circle.getRadius(), opt_angle);
+  return polygon;
+};
+
+
+/**
+ * Modify the coordinates of a polygon to make it a regular polygon.
+ * @param {ol.geom.Polygon} polygon Polygon geometry.
+ * @param {ol.Coordinate} center Center of the regular polygon.
+ * @param {number} radius Radius of the regular polygon.
+ * @param {number=} opt_angle Start angle for the first vertex of the polygon in
+ *     radians. Default is 0.
+ */
+ol.geom.Polygon.makeRegular = function(polygon, center, radius, opt_angle) {
+  var flatCoordinates = polygon.getFlatCoordinates();
+  var layout = polygon.getLayout();
+  var stride = polygon.getStride();
+  var ends = polygon.getEnds();
+  goog.asserts.assert(ends.length === 1, 'only 1 ring is supported');
+  var sides = flatCoordinates.length / stride - 1;
+  var startAngle = goog.isDef(opt_angle) ? opt_angle : 0;
+  var angle, coord, offset;
+  for (var i = 0; i <= sides; ++i) {
+    offset = i * stride;
+    angle = startAngle + (goog.math.modulo(i, sides) * 2 * Math.PI / sides);
+    flatCoordinates[offset] = center[0] + (radius * Math.cos(angle));
+    flatCoordinates[offset + 1] = center[1] + (radius * Math.sin(angle));
+  }
+  polygon.setFlatCoordinates(layout, flatCoordinates, ends);
+};

test/spec/ol/geom/polygon.test.js

@@ -436,10 +436,44 @@ describe('ol.geom.Polygon', function() {
     });
   });
 
+  describe('ol.geom.Polygon.fromCircle', function() {
+
+    it('creates a regular polygon', function() {
+      var circle = new ol.geom.Circle([0, 0, 0], 1, ol.geom.GeometryLayout.XYZ);
+      var polygon = ol.geom.Polygon.fromCircle(circle);
+      var coordinates = polygon.getLinearRing(0).getCoordinates();
+      expect(coordinates[0].length).to.eql(3);
+      expect(coordinates[0][2]).to.eql(0);
+      expect(coordinates[32]).to.eql(coordinates[0]);
+      // east
+      expect(coordinates[0][0]).to.roughlyEqual(1, 1e-9);
+      expect(coordinates[0][1]).to.roughlyEqual(0, 1e-9);
+      // south
+      expect(coordinates[8][0]).to.roughlyEqual(0, 1e-9);
+      expect(coordinates[8][1]).to.roughlyEqual(1, 1e-9);
+      // west
+      expect(coordinates[16][0]).to.roughlyEqual(-1, 1e-9);
+      expect(coordinates[16][1]).to.roughlyEqual(0, 1e-9);
+      // north
+      expect(coordinates[24][0]).to.roughlyEqual(0, 1e-9);
+      expect(coordinates[24][1]).to.roughlyEqual(-1, 1e-9);
+    });
+
+    it('creates a regular polygon with custom sides and angle', function() {
+      var circle = new ol.geom.Circle([0, 0], 1);
+      var polygon = ol.geom.Polygon.fromCircle(circle, 4, Math.PI / 2);
+      var coordinates = polygon.getLinearRing(0).getCoordinates();
+      expect(coordinates[4]).to.eql(coordinates[0]);
+      expect(coordinates[0][0]).to.roughlyEqual(0, 1e-9);
+      expect(coordinates[0][1]).to.roughlyEqual(1, 1e-9);
+    });
+  });
+
 });
 
 
 goog.require('ol.extent');
+goog.require('ol.geom.Circle');
 goog.require('ol.geom.GeometryLayout');
 goog.require('ol.geom.LinearRing');
 goog.require('ol.geom.Polygon');