Add map.getNumLayers(), map.getLayerIndex(), map.setLayerIndex(), map.raiseLayer() to support moving layers up and down in the map stack.

git-svn-id: http://svn.openlayers.org/trunk/openlayers@1604 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Map.js

@@ -255,14 +255,23 @@ OpenLayers.Map.prototype = {
         return foundLayer;
     },
 
+    /**
+    * @param {OpenLayers.Layer} layer
+    * @param {int} zIdx
+    * @private
+    */    
+    setLayerZIndex: function (layer, zIdx) {
+        layer.div.style.zIndex = 
+            this.Z_INDEX_BASE[layer.isBaseLayer ? 'BaseLayer' : 'Overlay']
+            + zIdx * 5;
+    },
+
     /**
     * @param {OpenLayers.Layer} layer
     */    
     addLayer: function (layer) {
         layer.div.style.overflow = "";
-        layer.div.style.zIndex = 
-            this.Z_INDEX_BASE[layer.isBaseLayer ? 'BaseLayer' : 'Overlay']
-            + this.layers.length * 5;
+        this.setLayerZIndex(layer, this.layers.length);
 
         if (layer.isFixed) {
             this.viewPortDiv.appendChild(layer.div);
@@ -346,6 +355,62 @@ OpenLayers.Map.prototype = {
         }
         this.events.triggerEvent("removelayer");
     },
+
+    /**
+    * @returns The number of layers attached to the map.
+    * @type int
+    */
+    getNumLayers: function () {
+        return this.layers.length;
+    },
+
+    /** 
+    * @returns The current (zero-based) index of the given layer in the map's
+    *     layer stack. Returns -1 if the layer isn't on the map.
+    *
+    * @param {OpenLayers.Layer} layer
+    * @type int
+    */
+    getLayerIndex: function (layer) {
+        return OpenLayers.Util.indexOf(this.layers, layer);
+    },
+    
+    /** Move the given layer to the specified (zero-based) index in the layer
+    *     list, changing its z-index in the map display. Use
+    *     map.getLayerIndex() to find out the current index of a layer. Note
+    *     that this cannot (or at least should not) be effectively used to
+    *     raise base layers above overlays.
+    *
+    * @param {OpenLayers.Layer} layer
+    * @param {int} idx
+    */
+    setLayerIndex: function (layer, idx) {
+        var base = this.getLayerIndex(layer);
+        if (idx < 0) 
+            idx = 0;
+        else if (idx > this.layers.length)
+            idx = this.layers.length;
+        if (base != idx) {
+            this.layers.splice(base, 1);
+            this.layers.splice(idx, 0, layer);
+            for (var i = 0; i < this.layers.length; i++)
+                this.setLayerZIndex(this.layers[i], i);
+            this.events.triggerEvent("changelayer");
+        }
+    },
+
+    /** Change the index of the given layer by delta. If delta is positive, 
+    *     the layer is moved up the map's layer stack; if delta is negative,
+    *     the layer is moved down.  Again, note that this cannot (or at least
+    *     should not) be effectively used to raise base layers above overlays.
+    *
+    * @param {OpenLayers.Layer} layer
+    * @param {int} idx
+    */
+    raiseLayer: function (layer, delta) {
+        var idx = this.getLayerIndex(layer) + delta;
+        this.setLayerIndex(layer, idx);
+    },
     
     /** Allows user to specify one of the currently-loaded layers as the Map's
      *   new base layer.