the mousewheel handler zooms the map by default

src/ol/handler/MouseWheel.js

@@ -1,8 +1,10 @@
 /**
- * @fileoverview Map Mouse Wheel Handler.
+ * @fileoverview Mouse Wheel Handler.
  *
  * Provides a class for listening to mousewheel events on a DOM element
  * and re-dispatching to a map instance.
+ *
+ * The default behabior is zooming the map.
  */
 
 goog.provide('ol.handler.MouseWheel');
@@ -34,7 +36,39 @@ ol.handler.MouseWheel = function(map, elt) {
 
     goog.events.listen(handler,
                        goog.events.MouseWheelHandler.EventType.MOUSEWHEEL,
-                       handleMouseWheel);
+                       this.handleMouseWheel, false, this);
 
 };
 goog.inherits(ol.handler.MouseWheel, goog.Disposable);
+
+/**
+ * @param {goog.events.MouseWheelEvent} e
+ */
+ol.handler.MouseWheel.prototype.handleMouseWheel = function(e) {
+    e.position = goog.style.getRelativePosition(e, this.elt_);
+    e.type = 'mousewheel';
+    var rt = goog.events.dispatchEvent(this.map_, e);
+    if (rt) {
+        this.defaultBehavior(e);
+    }
+};
+
+/**
+ * @param {goog.events.MouseWheelEvent} e
+ */
+ol.handler.MouseWheel.prototype.defaultBehavior = function(e) {
+    var me = this;
+    if (e.deltaY === 0 || me.zoomBlocked_) {
+        return;
+    }
+    me.zoomBlocked_ = window.setTimeout(function() {
+        me.zoomBlocked_ = null;
+    }, 200);
+
+    var map = me.map_,
+        step = e.deltaY / Math.abs(e.deltaY);
+    map.setZoom(map.getZoom() - step, e.position);
+
+    // We don't want the page to scroll.
+    e.preventDefault();
+};