new restrictedMinZoom property. r=bartvde (closes #3024)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@11058 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer.js

@@ -274,6 +274,18 @@ OpenLayers.Layer = OpenLayers.Class({
      * {Integer}
      */
     numZoomLevels: null,
+    
+    /**
+     * Property: restrictedMinZoom
+     * {Integer} Restriction of the minimum zoom level. This is used for layers
+     *     that only use a subset of the resolutions in the <resolutions>
+     *     array. This is independent of <numResolutions>, which always starts
+     *     counting at zoom level 0. If restrictedMinZoom is e.g. set to 2,
+     *     the first two zoom levels (0 and 1) will not be used by this layer.
+     *     If the layer is a base layer, zooming to the map's maxExtent means
+     *     setting the map's zoom to 2.
+     */
+    restrictedMinZoom: 0,
    
     /**
      * APIProperty: minScale
@@ -740,7 +752,8 @@ OpenLayers.Layer = OpenLayers.Class({
         } else {
             if (this.map) {
                 var resolution = this.map.getResolution();
-                inRange = ( (resolution >= this.minResolution) &&
+                inRange = ( this.map.getZoom() >= this.restrictedMinZoom &&
+                            (resolution >= this.minResolution) &&
                             (resolution <= this.maxResolution) );
             }
         }
@@ -1171,7 +1184,7 @@ OpenLayers.Layer = OpenLayers.Class({
             }
             zoom = Math.max(0, i-1);
         }
-        return zoom;
+        return Math.max(this.restrictedMinZoom, zoom);
     },
     
     /**

lib/OpenLayers/Map.js

@@ -1800,8 +1800,8 @@ OpenLayers.Map = OpenLayers.Class({
      *           within the min/max range of zoom levels.
      */
     isValidZoomLevel: function(zoomLevel) {
-       return ( (zoomLevel != null) &&
-                (zoomLevel >= 0) && 
+        return ( (zoomLevel != null) &&
+                (zoomLevel >= this.getRestrictedMinZoom()) && 
                 (zoomLevel < this.getNumZoomLevels()) );
     },
     
@@ -1905,6 +1905,20 @@ OpenLayers.Map = OpenLayers.Class({
         return maxExtent;
     },
     
+    /**
+     * Method: getRestricteMinZoom
+     *
+     * Returns:
+     * {Integer} the minimum zoom level allowed for the current baseLayer.
+     */
+    getRestrictedMinZoom: function() {
+        var minZoom = null;
+        if (this.baseLayer != null) {
+            minZoom = this.baseLayer.restrictedMinZoom;
+        }
+        return minZoom;
+    },
+    
     /**
      * APIMethod: getNumZoomLevels
      *