General purpose getCorner function for extents

src/ol/extent.js

@@ -1,5 +1,6 @@
 goog.provide('ol.Extent');
 goog.provide('ol.extent');
+goog.provide('ol.extent.Corner');
 goog.provide('ol.extent.Relationship');
 
 goog.require('goog.asserts');
@@ -17,6 +18,18 @@ goog.require('ol.TransformFunction');
 ol.Extent;
 
 
+/**
+ * Extent corner.
+ * @enum {string}
+ */
+ol.extent.Corner = {
+  BOTTOM_LEFT: 'bottom-left',
+  BOTTOM_RIGHT: 'bottom-right',
+  TOP_LEFT: 'top-left',
+  TOP_RIGHT: 'top-right'
+};
+
+
 /**
  * Relationship to an extent.
  * @enum {number}
@@ -456,6 +469,30 @@ ol.extent.getCenter = function(extent) {
 };
 
 
+/**
+ * Get a corner coordinate of an extent.
+ * @param {ol.Extent} extent Extent.
+ * @param {ol.extent.Corner} corner Corner.
+ * @return {ol.Coordinate} Corner coordinate.
+ */
+ol.extent.getCorner = function(extent, corner) {
+  var coordinate;
+  if (corner === ol.extent.Corner.BOTTOM_LEFT) {
+    coordinate = ol.extent.getBottomLeft(extent);
+  } else if (corner === ol.extent.Corner.BOTTOM_RIGHT) {
+    coordinate = ol.extent.getBottomRight(extent);
+  } else if (corner === ol.extent.Corner.TOP_LEFT) {
+    coordinate = ol.extent.getTopLeft(extent);
+  } else if (corner === ol.extent.Corner.TOP_RIGHT) {
+    coordinate = ol.extent.getTopRight(extent);
+  } else {
+    goog.asserts.fail('Invalid corner: %s', corner);
+  }
+  goog.asserts.assert(goog.isDef(coordinate));
+  return coordinate;
+};
+
+
 /**
  * @param {ol.Extent} extent1 Extent 1.
  * @param {ol.Extent} extent2 Extent 2.

test/spec/ol/extent.test.js

@@ -177,6 +177,31 @@ describe('ol.extent', function() {
     });
   });
 
+  describe('getCorner', function() {
+    var extent = [1, 2, 3, 4];
+
+    it('gets the bottom left', function() {
+      var corner = ol.extent.Corner.BOTTOM_LEFT;
+      expect(ol.extent.getCorner(extent, corner)).to.eql([1, 2]);
+    });
+
+    it('gets the bottom right', function() {
+      var corner = ol.extent.Corner.BOTTOM_RIGHT;
+      expect(ol.extent.getCorner(extent, corner)).to.eql([3, 2]);
+    });
+
+    it('gets the top left', function() {
+      var corner = ol.extent.Corner.TOP_LEFT;
+      expect(ol.extent.getCorner(extent, corner)).to.eql([1, 4]);
+    });
+
+    it('gets the top right', function() {
+      var corner = ol.extent.Corner.TOP_RIGHT;
+      expect(ol.extent.getCorner(extent, corner)).to.eql([3, 4]);
+    });
+
+  });
+
   describe('getForViewAndSize', function() {
 
     it('works for a unit square', function() {
@@ -538,5 +563,6 @@ describe('ol.extent', function() {
 
 goog.require('goog.vec.Mat4');
 goog.require('ol.extent');
+goog.require('ol.extent.Corner');
 goog.require('ol.extent.Relationship');
 goog.require('ol.proj');