Merge pull request #6966 from ahocevar/resolution-for-zoom

Add getResolutionForZoom method for ol.View

src/ol/view.js

@@ -809,6 +809,18 @@ ol.View.prototype.getZoomForResolution = function(resolution) {
 };
 
 
+/**
+ * Get the resolution for a zoom level.
+ * @param {number} zoom Zoom level.
+ * @return {number} The view resolution for the provided zoom level.
+ * @api
+ */
+ol.View.prototype.getResolutionForZoom = function(zoom) {
+  return /** @type {number} */ (this.constrainResolution(
+      this.maxResolution_, zoom - this.minZoom_, 0));
+};
+
+
 /**
  * Fit the given geometry or extent based on the given map size and border.
  * The size is pixel dimensions of the box to fit the extent into.
@@ -1025,9 +1037,7 @@ ol.View.prototype.setRotation = function(rotation) {
  * @api
  */
 ol.View.prototype.setZoom = function(zoom) {
-  var resolution = this.constrainResolution(
+  this.setResolution(this.getResolutionForZoom(zoom));
-      this.maxResolution_, zoom - this.minZoom_, 0);
-  this.setResolution(resolution);
 };
 
 

test/spec/ol/view.test.js

@@ -988,6 +988,31 @@ describe('ol.View', function() {
 
   });
 
+  describe('#getResolutionForZoom', function() {
+
+    it('returns correct zoom resolution', function() {
+      var view = new ol.View();
+      var max = view.getMaxZoom();
+      var min = view.getMinZoom();
+
+      expect(view.getResolutionForZoom(max)).to.be(view.getMinResolution());
+      expect(view.getResolutionForZoom(min)).to.be(view.getMaxResolution());
+    });
+
+    it('returns correct zoom levels for specifically configured resolutions', function() {
+      var view = new ol.View({
+        resolutions: [10, 8, 6, 4, 2]
+      });
+
+      expect(view.getResolutionForZoom(0)).to.be(10);
+      expect(view.getResolutionForZoom(1)).to.be(8);
+      expect(view.getResolutionForZoom(2)).to.be(6);
+      expect(view.getResolutionForZoom(3)).to.be(4);
+      expect(view.getResolutionForZoom(4)).to.be(2);
+    });
+
+  });
+
   describe('#getMaxZoom', function() {
 
     it('returns the zoom level for the min resolution', function() {