[GIS] Capturing/overriding mousewheel zoom in openlayers

javascriptopenlayers-2

So I've created a map in openlayers and I am setting it up so that there are only certain zoom levels a user can see. I have the code created to handle forcing a user to the next acceptable zoom level when they attempt to zoom in/out. I have been able to create listener for handling double-clicks (see code below) but for the life of me I cannot figure out how to capture mousewheel events.

The documentation makes it seem like it should be straightforward but I've been banging my head against a wall for more than a day trying to figure this out. All my googling has turned up plenty of results for disabling the mousewheel but nothing for capturing wheel events.

function init() {
    map = new OpenLayers.Map('map_canvas',mapSettings);
    ....
    ....
    );

    var click = new OpenLayers.Control.Click();
    map.addControl(click);
    click.activate();
}

OpenLayers.Control.Click = OpenLayers.Class(OpenLayers.Control, {
    defaultHandlerOptions: {
    'single': false,
    'double': true,
    'pixelTolerance': 0,
    'stopSingle': false,
    'stopDouble': false
    },

    initialize: function(options) {
        this.handlerOptions = OpenLayers.Util.extend(
        {}, this.defaultHandlerOptions
        );
        OpenLayers.Control.prototype.initialize.apply(
        this, arguments
        );
        this.handler = new OpenLayers.Handler.Click(
        this, {
        'dblclick': this.trigger
        }, this.handlerOptions
        );
    },

    trigger: function(e) {
        var lonlat = map.getLonLatFromViewPortPx(e.xy);
        curZoom = map.getZoom();
        var newZoom = stepZoomIn(map.getZoom());
        updateMapZoom(newZoom);
        map.setCenter(event.lonlat);
    }

});

Best Answer

I was able to accomplish this by defining my own control derived from Navigation control.

var NavigationControl = OpenLayers.Class(OpenLayers.Control.Navigation, {
  wheelDown: function(evt, delta) {
    if (canZoomOut()) {
      return OpenLayers.Control.Navigation.prototype.wheelDown.apply(this,arguments);
    } else {
      console.log('Blocked user of zooming out');
    }
  }
});

map.addControl(new NavigationControl());

This of course will work only as long as Navigation control defines wheelDown - function. If Navigation control is modified in later OpenLayers version then this will brake as well.

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