part two of #204 -- all that remains is to write some test functions

git-svn-id: http://svn.openlayers.org/trunk/openlayers@1383 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer.js

@@ -336,20 +336,24 @@ OpenLayers.Layer.prototype = {
 
     /** Calculates based on resolution, center, and mapsize
      * 
+     * @param {float} resolution Specific resolution to get an extent for.
+     *                           If null, this.getResolution() is called
      * @returns A Bounds object which represents the lon/lat bounds of the 
      *          current viewPort.
      * @type OpenLayers.Bounds
      */
-    getExtent: function () {
+    getExtent: function(resolution) {
         var extent = null;
 
         var center = this.map.getCenter();
         if (center != null) {
 
-            var res = this.getResolution();
+            if (resolution == null) {
+                resolution = this.getResolution();
+            }
             var size = this.map.getSize();
-            var w_deg = size.w * res;
+            var w_deg = size.w * resolution;
-            var h_deg = size.h * res;
+            var h_deg = size.h * resolution;
 
             extent = new OpenLayers.Bounds(center.lon - w_deg / 2,
                                            center.lat - h_deg / 2,

lib/OpenLayers/Layer/FixedZoomLevels.js

@@ -27,6 +27,11 @@
  *    taken from the pixel locations (0,0) and the size of the map. But how 
  *    will we be able to do lonlat-px translation without resolution....?
  * 
+ *   The getZoomForResolution() method is overridden. Instead of indexing into
+ *    the resolutions[] array, we call OpenLayers.Layer.getExent(), passing in
+ *    the desired resolution. With this extent, we then call getZoomForExtent() 
+ * 
+ * 
  *   Whenever you implement a layer using OpenLayers.Layer.FixedZoomLevels, 
  *    it is your responsibility to provide the following three functions:
  * 
@@ -107,6 +112,21 @@ OpenLayers.Layer.FixedZoomLevels.prototype = {
         return extent;
     },
 
+    /**
+     * @param {float} resolution
+     *
+     * @returns A suitable zoom level for the specified resolution.
+     *          If no baselayer is set, returns null.
+     * @type int
+     */
+    getZoomForResolution: function(resolution) {
+      
+        var extent = OpenLayers.Layer.prototype.getExtent.apply(this, 
+                                                                [resolution]);
+                                                                
+        return this.getZoomForExtent(extent);
+    },
+
     /** @final @type String */
     CLASS_NAME: "FixedZoomLevels.js"
 };