rem: lonlat = new OpenLayers.LonLat(center.lon + delta_x * res , center.lat - delta_y * res); 
add: lonlat = new OpenLayers.LonLat(center.lon + delta_x * res , center.lat - delta_y * res); } 
context:     getLonLatFromViewPortPx: function (viewPortPx) {        var lonlat = null;        if (viewPortPx != null) {            var size = this.map.getSize();            var center = this.map.getCenter();            var res  = this.map.getResolution();                    var delta_x = viewPortPx.x - (size.w / 2);            var delta_y = viewPortPx.y - (size.h / 2);                        lonlat = new OpenLayers.LonLat(center.lon + delta_x * res ,                                         center.lat - delta_y * res);         }        return lonlat;    },
meta: 1027	/local1/tlutelli/issta_data/temp/all_js/javascript/2007_temp/2007/1027/c5bbc39b4a8b86a6d19238ffab1a6e15ce7ae296/Layer.js/clean/lib/OpenLayers/Layer.js