Layer.TileCache, Layer.TMS: support a subset of server resolutions. r=tschaub (closes #1944)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@8932 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/TileCache.js

@@ -33,6 +33,13 @@ OpenLayers.Layer.TileCache = OpenLayers.Class(OpenLayers.Layer.Grid, {
      */
     format: 'image/png',
 
+    /**
+     * APIProperty: serverResolutions
+     * {Array} A list of all resolutions available on the server.  Only set this 
+     *     property if the map resolutions differs from the server.
+     */
+    serverResolutions: null,
+
     /**
      * Constructor: OpenLayers.Layer.TileCache
      * Create a new read only TileCache layer.
@@ -98,7 +105,7 @@ OpenLayers.Layer.TileCache = OpenLayers.Class(OpenLayers.Layer.Grid, {
         var size = this.tileSize;
         var tileX = Math.round((bounds.left - bbox.left) / (res * size.w));
         var tileY = Math.round((bounds.bottom - bbox.bottom) / (res * size.h));
-        var tileZ = this.map.zoom;
+        var tileZ = this.serverResolutions != null ? this.serverResolutions.indexOf(res) : this.map.getZoom();
         /**
          * Zero-pad a positive integer.
          * number - {Int}