add onScreen() function to OpenLayers.Feature, and add tests to prove it.

git-svn-id: http://svn.openlayers.org/trunk/openlayers@1510 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Feature.js

@@ -72,6 +72,21 @@ OpenLayers.Feature.prototype= {
         }
     },
     
+    /**
+     * @returns Whether or not the feature is currently visible on screen
+     *           (based on its 'lonlat' property)
+     * @type Boolean
+     */
+    onScreen:function() {
+        
+        var onScreen = false;
+        if ((this.layer != null) && (this.layer.map != null)) {
+            var screenBounds = this.layer.map.getExtent();
+            onScreen = screenBounds.containsLonLat(this.lonlat);
+        }    
+        return onScreen;
+    },
+    
 
     /**
      * @returns A Marker Object created from the 'lonlat' and 'icon' properties

tests/test_Feature.html

@@ -76,6 +76,32 @@
               "Layer div img contains correct url" );
 */
     }
+    
+    function test_03_Feature_onScreen(t) {
+        t.plan( 2 );
+
+        var map = new OpenLayers.Map("map");
+
+        var url = "http://octo.metacarta.com/cgi-bin/mapserv";
+        var wms = new OpenLayers.Layer.WMS(name, url);
+
+        map.addLayer(wms);
+
+        var layer = new OpenLayers.Layer("foo");
+        map.addLayer(layer);
+        
+        map.zoomToExtent(new OpenLayers.Bounds(-50,-50,50,50));
+
+        //onscreen feature
+        var feature1 = new OpenLayers.Feature(layer, 
+                                              new OpenLayers.LonLat(0,0));
+        t.ok( feature1.onScreen(), "feature knows it's onscreen" );
+
+        //onscreen feature
+        var feature2 = new OpenLayers.Feature(layer, 
+                                              new OpenLayers.LonLat(100,100));
+        t.ok( !feature2.onScreen(), "feature knows it's offscreen" );
+    }
 
   // -->
   </script>