Handler for wheel up/down events.
| OpenLayers. | Handler for wheel up/down events. | 
| Properties | |
| wheelListener | {function} | 
| mousePosition | {OpenLayers.Pixel} mousePosition is necessary because evt.clientX/Y is buggy in Moz on wheel events, so we cache and use the value from the last mousemove. | 
| interval | {Integer} In order to increase server performance, an interval (in milliseconds) can be set to reduce the number of up/down events called. | 
| delta | {Integer} When interval is set, delta collects the mousewheel z-deltas of the events that occur within the interval. | 
| cumulative | {Boolean} When interval is set: true to collect all the mousewheel z-deltas, false to only record the delta direction (positive or negative) | 
| Constructor | |
| OpenLayers. | |
| Functions | |
| destroy | |
| onWheelEvent | Catch the wheel event and handle it xbrowserly | 
| wheelZoom | Given the wheel event, we carry out the appropriate zooming in or out, based on the ‘wheelDelta’ or ‘detail’ property of the event. | 
| mousemove | Update the stored mousePosition on every move. | 
| activate | |
| deactivate | 
{OpenLayers.Pixel} mousePosition is necessary because evt.clientX/Y is buggy in Moz on wheel events, so we cache and use the value from the last mousemove.
| control | {OpenLayers.Control} | 
| callbacks | {Object} An object containing a single function to be called when the drag operation is finished. The callback should expect to recieve a single argument, the point geometry. | 
| options | {Object} | 
destroy: function() 
Catch the wheel event and handle it xbrowserly
onWheelEvent: function( e ) 
Given the wheel event, we carry out the appropriate zooming in or out, based on the ‘wheelDelta’ or ‘detail’ property of the event.
wheelZoom: function( e ) 
Update the stored mousePosition on every move.
mousemove: function ( evt ) 
activate: function ( evt ) 
deactivate: function ( evt )