Add a snapToZero rotation constraint

src/ol/rotationconstraint.js

@@ -37,3 +37,23 @@ ol.RotationConstraint.createSnapToN = function(n) {
     }
   };
 };
+
+
+/**
+ * @param {number=} opt_tolerance Tolerance.
+ * @return {ol.RotationConstraintType} Rotation constraint.
+ */
+ol.RotationConstraint.createSnapToZero = function(opt_tolerance) {
+  var tolerance = opt_tolerance || 0.1;
+  return function(rotation, delta) {
+    if (goog.isDef(rotation)) {
+      if (Math.abs(rotation + delta) <= tolerance) {
+        return 0;
+      } else {
+        return rotation + delta;
+      }
+    } else {
+      return undefined;
+    }
+  };
+};

src/ol/view2d.js

@@ -387,6 +387,6 @@ ol.View2D.createConstraints_ = function(view2DOptions) {
         zoomFactor, maxResolution, numZoomLevels - 1);
   }
   // FIXME rotation constraint is not configurable at the moment
-  var rotationConstraint = ol.RotationConstraint.none;
+  var rotationConstraint = ol.RotationConstraint.createSnapToZero();
   return new ol.Constraints(resolutionConstraint, rotationConstraint);
 };

test/spec/ol/rotationconstraint.test.js

@@ -0,0 +1,36 @@
+goog.provide('ol.test.RotationConstraint');
+
+describe('ol.RotationConstraint', function() {
+
+  describe('SnapToZero', function() {
+
+    it('returns expected rotation value', function() {
+      var rotationConstraint = ol.RotationConstraint.createSnapToZero(0.3);
+
+      expect(rotationConstraint(0.1, 0)).toEqual(0);
+      expect(rotationConstraint(0.2, 0)).toEqual(0);
+      expect(rotationConstraint(0.3, 0)).toEqual(0);
+      expect(rotationConstraint(0.4, 0)).toEqual(0.4);
+
+      expect(rotationConstraint(-0.1, 0)).toEqual(0);
+      expect(rotationConstraint(-0.2, 0)).toEqual(0);
+      expect(rotationConstraint(-0.3, 0)).toEqual(0);
+      expect(rotationConstraint(-0.4, 0)).toEqual(-0.4);
+
+      expect(rotationConstraint(1, -0.9)).toEqual(0);
+      expect(rotationConstraint(1, -0.8)).toEqual(0);
+      // floating-point arithmetic
+      expect(rotationConstraint(1, -0.7)).not.toEqual(0);
+      expect(rotationConstraint(1, -0.6)).toEqual(0.4);
+
+      expect(rotationConstraint(-1, 0.9)).toEqual(0);
+      expect(rotationConstraint(-1, 0.8)).toEqual(0);
+      // floating-point arithmetic
+      expect(rotationConstraint(-1, 0.7)).not.toEqual(0);
+      expect(rotationConstraint(-1, 0.6)).toEqual(-0.4);
+    });
+
+  });
+});
+
+goog.require('ol.RotationConstraint');

test/spec/ol/view2d.test.js

@@ -49,6 +49,16 @@ describe('ol.View2D', function() {
       });
 
     });
+
+    describe('create rotation constraint', function() {
+      it('gives a correct rotation constraint function', function() {
+        var options = {};
+        var fn = ol.View2D.createConstraints_(options).rotation;
+        expect(fn(0.01, 0)).toEqual(0);
+        expect(fn(0.15, 0)).toEqual(0.15);
+      });
+    });
+
   });
 });