apply patch-3531-A0.diff from trac ticket #3531

lib/OpenLayers/Layer/XYZ.js

@@ -49,7 +49,16 @@ OpenLayers.Layer.XYZ = OpenLayers.Class(OpenLayers.Layer.Grid, {
     /**
      * APIProperty: serverResolutions
      * {Array} A list of all resolutions available on the server.  Only set this
-     *     property if the map resolutions differs from the server.
+     *     property if the map resolutions differ from the server. This
+     *     property serves two purposes. (a) <serverResolutions> can include
+     *     resolutions that the server supports and that you don't want to
+     *     provide with this layer; you can also look at <zoomOffset>, which is
+     *     an alternative to <serverResolutions> for that specific purpose.
+     *     (b) The map can work with resolutions that aren't supported by
+     *     the server, i.e. that aren't in <serverResolutions>. When the
+     *     map is displayed in such a resolution data for the closest
+     *     server-supported resolution is loaded and the layer div is
+     *     stretched as necessary.
      */
     serverResolutions: null,
 
@@ -139,7 +148,7 @@ OpenLayers.Layer.XYZ = OpenLayers.Class(OpenLayers.Layer.Grid, {
      * {Object} - an object with x, y and z properties.
      */
     getXYZ: function(bounds) {
-        var res = this.map.getResolution();
+        var res = this.getServerResolution();
         var x = Math.round((bounds.left - this.maxExtent.left) /
             (res * this.tileSize.w));
         var y = Math.round((this.maxExtent.top - bounds.top) /
@@ -147,7 +156,7 @@ OpenLayers.Layer.XYZ = OpenLayers.Class(OpenLayers.Layer.Grid, {
         var resolutions = this.serverResolutions || this.resolutions;
         var z = this.zoomOffset == 0 ?
             OpenLayers.Util.indexOf(resolutions, res) :
-            this.map.getZoom() + this.zoomOffset;
+            this.getServerZoom() + this.zoomOffset;
 
         var limit = Math.pow(2, z);
         if (this.wrapDateLine)