Allow registration of custom functions for expressions

examples/vector-layer.js

@@ -1,8 +1,7 @@
-goog.require('ol.Expression');
 goog.require('ol.Map');
 goog.require('ol.RendererHint');
 goog.require('ol.View2D');
-goog.require('ol.filter.Filter');
+goog.require('ol.expression');
 goog.require('ol.layer.TileLayer');
 goog.require('ol.layer.Vector');
 goog.require('ol.parser.GeoJSON');
@@ -19,6 +18,11 @@ var raster = new ol.layer.TileLayer({
   source: new ol.source.MapQuestOpenAerial()
 });
 
+// TODO: discuss scale dependent rules
+ol.expression.register('resolution', function() {
+  return map.getView().getView2D().getResolution();
+});
+
 var vector = new ol.layer.Vector({
   source: new ol.source.Vector({
     projection: ol.proj.get('EPSG:4326')
@@ -32,13 +36,11 @@ var vector = new ol.layer.Vector({
       ]
     }),
     new ol.style.Rule({
-      filter: new ol.filter.Filter(function() {
-        return map.getView().getResolution() < 5000;
-      }),
+      filter: 'resolution() < 5000',
       symbolizers: [
         new ol.style.Text({
           color: '#bada55',
-          text: new ol.Expression('name'),
+          text: ol.expression.parse('name'),
           fontFamily: 'Calibri,sans-serif',
           fontSize: 12
         })