JSDOC and small update to use Pixel diff code

git-svn-id: http://svn.openlayers.org/trunk/openlayers@123 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Marker.js

@@ -27,16 +27,23 @@ OpenLayers.Marker.prototype = {
         this.icon = icon;
         this.lonlat = lonlat;
     },
+    
+    /** 
+    * @param {OpenLayers.Pixel} pixel
+    * 
+    * @return A new DOM Image with this marker<65>s icon set at the 
+    *         location passed-in
+    * @type DOMElement
+    */
     generateMarker: function(pixel) {
         // Create a div here, and set the location to the pixel above modified
         // by the icon size.
-        var markerObject = OpenLayers.Util.createImage(
-            this.icon.url,
-            this.icon.size,
-            new OpenLayers.Pixel(
-              pixel.x-(this.icon.size.w/2), 
-              pixel.y-this.icon.size.h)
-            );
+        var markerOffset = new OpenLayers.Pixel(this.icon.size.w / 2, 
+                                                this.icon.size.h);
+        var iconPosition = pixel.diff(markerOffset);
+        var markerObject = OpenLayers.Util.createImage(this.icon.url,
+                                                       this.icon.size,
+                                                       iconPosition);
         return markerObject;
     } 
 }