add getDataExtent() method to layer (experimental) and to markers layer (api supported). thanks for the feature request and original patch, anonymous ol-er :-) (Closes #750)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@4051 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer.js

@@ -723,6 +723,18 @@ OpenLayers.Layer = OpenLayers.Class({
         return this.getZoomForResolution(idealResolution);
     },
     
+    /** 
+     * Method: getDataExtent
+     * Calculates the max extent which includes all of the data for the layer.
+     *     This function is to be implemented by subclasses.
+     * 
+     * Returns:
+     * {<OpenLayers.Bounds>}
+     */
+    getDataExtent: function () {
+        //to be implemented by subclasses
+    },
+
     /**
      * APIMethod: getZoomForResolution
      * 

lib/OpenLayers/Layer/Markers.js

@@ -139,6 +139,27 @@ OpenLayers.Layer.Markers = OpenLayers.Class(OpenLayers.Layer, {
             }
         }
     },
+    
+    /** 
+     * APIMethod: getDataExtent
+     * Calculates the max extent which includes all of the markers.
+     * 
+     * Returns:
+     * {<OpenLayers.Bounds>}
+     */
+    getDataExtent: function () {
+        var maxExtent = null;
+        
+        if ( this.markers && (this.markers.length > 0)) {
+            var maxExtent = new OpenLayers.Bounds();
+            for(var i=0; i < this.markers.length; i++) {
+                var marker = this.markers[i];
+                maxExtent.extend(marker.lonlat);
+            }
+        }
+
+        return maxExtent;
+    },
 
     CLASS_NAME: "OpenLayers.Layer.Markers"
 });