Add ol.View2D#getZoom

src/ol/view2d.js

@@ -325,6 +325,31 @@ ol.View2D.prototype.getView3D = function() {
 };
 
 
+/**
+ * Get the current zoom level. Return undefined if the current
+ * resolution is undefined or not a "constrained resolution".
+ * @return {number|undefined} Zoom.
+ */
+ol.View2D.prototype.getZoom = function() {
+  var zoom;
+  var resolution = this.getResolution();
+
+  if (goog.isDef(resolution)) {
+    var res, z = 0;
+    do {
+      res = this.constrainResolution(this.maxResolution_, z);
+      if (res == resolution) {
+        zoom = z;
+        break;
+      }
+      ++z;
+    } while (res > this.minResolution_);
+  }
+
+  return zoom;
+};
+
+
 /**
  * Fit the given extent based on the given map size.
  * @param {ol.Extent} extent Extent.

test/spec/ol/view2d.test.js

@@ -70,6 +70,38 @@ describe('ol.View2D', function() {
     });
 
   });
+
+  describe('#getZoom', function() {
+    var view;
+    beforeEach(function() {
+      view = new ol.View2D({
+        resolutions: [512, 256, 128, 64, 32, 16]
+      });
+    });
+
+    it('returns correct zoom levels', function() {
+      view.setResolution(undefined);
+      expect(view.getZoom()).to.be(undefined);
+
+      view.setResolution(511);
+      expect(view.getZoom()).to.be(undefined);
+
+      view.setResolution(512);
+      expect(view.getZoom()).to.be(0);
+
+      view.setResolution(64);
+      expect(view.getZoom()).to.be(3);
+
+      view.setResolution(65);
+      expect(view.getZoom()).to.be(undefined);
+
+      view.setResolution(16);
+      expect(view.getZoom()).to.be(5);
+
+      view.setResolution(15);
+      expect(view.getZoom()).to.be(undefined);
+    });
+  });
 });
 
 goog.require('ol.View2D');