adding getPixelFromLonLat() function to Map.js -- the code is lifted from OpenLayers.Layer.Marker's drawMarker() function. also test added to ensure both translation functions return valid objects and that going back and forth is consistent. Note that i only test pixel-lonlat-pixel, because going from lonlat-pixel-lonlat there is loss due to the rounding in the lonlat-pixel phase

git-svn-id: http://svn.openlayers.org/trunk/openlayers@246 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Map.js

@@ -271,6 +271,23 @@ OpenLayers.Map.prototype = {
                                      center.lat - delta_y * res); 
     },
 
+    /**
+    * @param {OpenLayers.LonLat} lonlat
+    *
+    * @returns An OpenLayers.Pixel which is the passed-in OpenLayers.LonLat, 
+    *          translated into screen pixels given the current extent 
+    *          and resolution
+    * @type OpenLayers.Pixel
+    */
+    getPixelFromLonLat: function (lonlat) {
+        var resolution = this.getResolution();
+        var extent = this.getExtent();
+        return new OpenLayers.Pixel(
+                       Math.round(1/resolution * (lonlat.lon - extent.left)),
+                       Math.round(1/resolution * (extent.top - lonlat.lat))
+                       );    
+    },
+
     /**
     * @param {OpenLayers.LonLat} lonlat
     * @param {int} zoom