Added Polygon.Perimeter

Author: jorbascrumps

src/geom/polygon/Perimeter.js

@@ -0,0 +1,42 @@
+/**
+ * @author       Richard Davey <rich@photonstorm.com>
+ * @copyright    2018 Photon Storm Ltd.
+ * @license      {@link https://github.com/photonstorm/phaser/blob/master/license.txt|MIT License}
+ */
+
+var Length = require('../line/Length');
+var Line = require('../line/Line');
+
+/**
+ * Returns the perimeter of the given Polygon.
+ *
+ * @function Phaser.Geom.Polygon.Perimeter
+ * @since 3.12.0
+ *
+ * @param {Phaser.Geom.Polygon} polygon - The Polygon to get the perimeter of.
+ *
+ * @return {number} The perimeter of the Polygon.
+ */
+var Perimeter = function (polygon)
+{
+    var points = polygon.points;
+    var perimeter = 0;
+
+    for (var i = 0; i < points.length; i++)
+    {
+        var pointA = points[i];
+        var pointB = points[(i + 1) % points.length];
+        var line = new Line(
+            pointA.x,
+            pointA.y,
+            pointB.x,
+            pointB.y
+        );
+
+        perimeter += Length(line);
+    }
+
+    return perimeter;
+};
+
+module.exports = Perimeter;

src/geom/polygon/index.js

@@ -11,5 +11,6 @@ Polygon.Contains = require('./Contains');
 Polygon.ContainsPoint = require('./ContainsPoint');
 Polygon.GetAABB = require('./GetAABB');
 Polygon.GetNumberArray = require('./GetNumberArray');
+Polygon.Perimeter = require('./Perimeter');
 
 module.exports = Polygon;