SelectFeature control can now select across multiple vector

layers when passed an array of layers instead of a single layer with 
the constructor. This changeset also introduces a new layer type, 
Layer.Vector.RootContainer, which will be set as the topmost layer by 
the SelectFeature control and collect the svg/vml/canvas roots of 
multiple vector layers. r=crschmidt (closes #1666)


git-svn-id: http://svn.openlayers.org/trunk/openlayers@9116 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Renderer.js

@@ -27,6 +27,12 @@ OpenLayers.Renderer = OpenLayers.Class({
      */
     container: null,
     
+    /**
+     * Property: root
+     * {DOMElement}
+     */
+    root: null,
+
     /** 
      * Property: extent
      * {<OpenLayers.Bounds>}
@@ -237,6 +243,32 @@ OpenLayers.Renderer = OpenLayers.Class({
      * geometry - {<OpenLayers.Geometry>} 
      */
     eraseGeometry: function(geometry) {},
+    
+    /**
+     * Method: moveRoot
+     * moves this renderer's root to a (different) renderer.
+     * To be implemented by subclasses that require a common renderer root for
+     * feature selection.
+     * 
+     * Parameters:
+     * renderer - {<OpenLayers.Renderer>} target renderer for the moved root
+     */
+    moveRoot: function(renderer) {},
+
+    /**
+     * Method: getRenderLayer
+     * Gets the layer that this renderer's output appears on. If moveRoot was
+     * used, this will be different from the layer containing the features
+     * rendered by this renderer.
+     * To be overridden by subclasses that implement moveRoot.
+     * 
+     * Returns:
+     * {<OpenLayers.Layer.Vector>} the output layer, if any (i.e. this method
+     * will not return a layer if the layer is not added to a map).
+     */
+    getRenderLayer: function() {
+        return this.map.getLayer(this.container.id);
+    },
 
     CLASS_NAME: "OpenLayers.Renderer"
 });