Function to buffer an extent

src/ol/extent.js

@@ -52,6 +52,19 @@ ol.extent.boundingExtentXYs_ = function(xs, ys, opt_extent) {
 };
 
 
+/**
+ * Increase an extent by the provided value.
+ * @param {ol.Extent} extent The extent to buffer.
+ * @param {number} value The amount by wich the extent should be buffered.
+ */
+ol.extent.buffer = function(extent, value) {
+  extent[0] -= value;
+  extent[1] -= value;
+  extent[2] += value;
+  extent[3] += value;
+};
+
+
 /**
  * Creates a clone of an extent.
  *

test/spec/ol/extent.test.js

@@ -3,6 +3,16 @@ goog.provide('ol.test.extent');
 
 describe('ol.extent', function() {
 
+  describe('buffer', function() {
+
+    it('buffers an extent by some value', function() {
+      var extent = [-10, -20, 10, 20];
+      ol.extent.buffer(extent, 15);
+      expect(extent).to.eql([-25, -35, 25, 35]);
+    });
+
+  });
+
   describe('clone', function() {
 
     it('creates a copy of an extent', function() {