Rectangle.RandomOutside is a new function that takes two Rectangles, outer and inner, and returns a random point that falls within the outer rectangle but is always outside of the inner rectangle.

Author: photonstorm

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### New Features
 
 * RenderTexture.resize will allow you to resize the underlying Render Texture to the new dimensions given. Doing this also clears the Render Texture at the same time (thanks @saqsun)
+* Rectangle.RandomOutside is a new function that takes two Rectangles, `outer` and `inner`, and returns a random point that falls within the outer rectangle but is always outside of the inner rectangle.
 
 ### Updates
 

src/geom/rectangle/RandomOutside.js

@@ -0,0 +1,69 @@
+/**
+ * @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 Between = require('../../math/Between');
+var ContainsRect = require('./ContainsRect');
+var Point = require('../point/Point');
+
+/**
+ * Calculates a random point that lies within the `outer` Rectangle, but outside of the `inner` Rectangle.
+ * The inner Rectangle must be fully contained within the outer rectangle.
+ *
+ * @function Phaser.Geom.Rectangle.RandomOutside
+ * @since 3.10.0
+ *
+ * @generic {Phaser.Geom.Point} O - [out,$return]
+ *
+ * @param {Phaser.Geom.Rectangle} outer - The outer Rectangle to get the random point within.
+ * @param {Phaser.Geom.Rectangle} inner - The inner Rectangle to exclude from the returned point.
+ * @param {Phaser.Geom.Point} [out] - A Point, or Point-like object to store the result in. If not specified, a new Point will be created.
+ *
+ * @return {Phaser.Geom.Point} A Point object containing the random values in its `x` and `y` properties.
+ */
+var RandomOutside = function (outer, inner, out)
+{
+    if (out === undefined) { out = new Point(); }
+
+    if (ContainsRect(outer, inner))
+    {
+        //  Pick a random quadrant
+        //  
+        //  The quadrants don't extend the full widths / heights of the outer rect to give
+        //  us a better uniformed distribution, otherwise you get clumping in the corners where
+        //  the 4 quads would overlap
+
+        switch (Between(0, 3))
+        {
+            //  Top
+            case 0:
+                out.x = outer.x + (Math.random() * (inner.right - outer.x));
+                out.y = outer.y + (Math.random() * (inner.top - outer.y));
+                break;
+
+            //  Bottom
+            case 1:
+                out.x = inner.x + (Math.random() * (outer.right - inner.x));
+                out.y = inner.bottom + (Math.random() * (outer.bottom - inner.bottom));
+                break;
+
+            //  Left
+            case 2:
+                out.x = outer.x + (Math.random() * (inner.x - outer.x));
+                out.y = inner.y + (Math.random() * (outer.bottom - inner.y));
+                break;
+
+            //  Right
+            case 3:
+                out.x = inner.right + (Math.random() * (outer.right - inner.right));
+                out.y = outer.y + (Math.random() * (inner.bottom - outer.y));
+                break;
+        }
+    }
+
+    return out;
+};
+
+module.exports = RandomOutside;

src/geom/rectangle/index.js

@@ -38,6 +38,7 @@ Rectangle.Overlaps = require('./Overlaps');
 Rectangle.Perimeter = require('./Perimeter');
 Rectangle.PerimeterPoint = require('./PerimeterPoint');
 Rectangle.Random = require('./Random');
+Rectangle.RandomOutside = require('./RandomOutside');
 Rectangle.Scale = require('./Scale');
 Rectangle.Union = require('./Union');