fix Bing layer's zoom level management. r=tschaub (closes #2987)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@10997 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/Bing.js

@@ -18,35 +18,6 @@
  */
 OpenLayers.Layer.Bing = OpenLayers.Class(OpenLayers.Layer.XYZ, {
 
-    /**
-     * Constant: RESOLUTIONS
-     */
-    RESOLUTIONS: [
-        78271.517,
-        39135.7585,
-        19567.87925,
-        9783.939625,
-        4891.9698125,
-        2445.98490625,
-        1222.992453125,
-        611.4962265625,
-        305.74811328125,
-        152.874056640625,
-        76.4370283203125,
-        38.21851416015625,
-        19.109257080078127,
-        9.554628540039063,
-        4.777314270019532,
-        2.388657135009766,
-        1.194328567504883,
-        0.5971642837524415,
-        0.29858214187622073,
-        0.14929107093811037,
-        0.07464553546905518,
-        0.03732276773452759,
-        0.018661383867263796
-    ],
-
     /**
      * Property: attributionTemplate
      * {String}
@@ -58,12 +29,6 @@ OpenLayers.Layer.Bing = OpenLayers.Class(OpenLayers.Layer.XYZ, {
          'href="http://www.microsoft.com/maps/product/terms.html">' +
          'Terms of Use</a></span>',
 
-    /**
-     * Property: sphericalMercator
-     * {Boolean} always true for this layer type
-     */
-    sphericalMercator: true,
-    
     /**
      * Property: metadata
      * {Object} Metadata for this layer, as returned by the callback script
@@ -131,7 +96,14 @@ OpenLayers.Layer.Bing = OpenLayers.Class(OpenLayers.Layer.XYZ, {
             OpenLayers.Layer.Bing.prototype.EVENT_TYPES.concat(
             OpenLayers.Layer.prototype.EVENT_TYPES
         );
+        
+        options = OpenLayers.Util.applyDefaults({
+            zoomOffset: 1,
+            maxResolution: 78271.51695,
+            sphericalMercator: true
+        }, options)
         var name = options.name || "Bing " + (options.type || this.type);
+        
         var newArgs = [name, null, options];
         OpenLayers.Layer.XYZ.prototype.initialize.apply(this, newArgs);
         this.loadMetadata(this.type); 
@@ -172,15 +144,22 @@ OpenLayers.Layer.Bing = OpenLayers.Class(OpenLayers.Layer.XYZ, {
         for (var i=0; i<res.imageUrlSubdomains.length; ++i) {
             this.url.push(url.replace("{subdomain}", res.imageUrlSubdomains[i]));
         };
-        
-        this.addOptions({
-            resolutions: this.RESOLUTIONS.slice(res.zoomMin-1, res.zoomMax-1),
-            zoomOffset: res.zoomMin
-        });
-        if (this.map) {
-            this.redraw();
-            this.updateAttribution();
+        var resolution;
+        if (this.map && this.map.baseLayer === this && this.map.getCenter()) {
+            // if we are the current base layer and the map was centered
+            // already, we need to remember the current resolution to find a
+            // matching zoom level after the maxResolution changes
+            resolution = this.getResolution();
         }
+        this.addOptions({
+            maxResolution: 78271.51695 / Math.pow(2, res.zoomMin - 1),
+            numZoomLevels: res.zoomMax - res.zoomMin + 1
+        });
+        // adjust zoom level to match the previous resolution - this triggers a
+        // moveTo on all layers.
+        resolution && this.map.zoomTo(this.getZoomForResolution(resolution));
+        // redraw to replace "blank.gif" tiles with real tiles
+        this.redraw();
     },
 
     /**