* Style and Rule now have separate context properties

* new convenience method addUniqueValueRules in OL.!StyleMap. This can actually be used to achieve what I was trying to show in the example of this ticket's description.
 * some refactoring of OL.Style to remove duplicate code (with tests)
 * a new example showing how to add a "unique value" legend to a point layer using the new addUniqueValueRules method
 * Rule.symbolizer can now also be just a symbolizer, instead of a hash of symbolizers keyed by "Point", "Line", "Polygon". This will make things even simpler (as can be seen in the styles-unique.html example)

r=tschaub (closes #1373)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@6396 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/StyleMap.js

@@ -110,6 +110,32 @@ OpenLayers.StyleMap = OpenLayers.Class({
         return OpenLayers.Util.extend(defaultSymbolizer,
             this.styles[intent].createSymbolizer(feature));
     },
+    
+    /**
+     * Method: addUniqueValueRules
+     * Convenience method to create comparison rules for unique values of a
+     * property. The rules will be added to the style object for a specified
+     * rendering intent. This method is a shortcut for creating something like
+     * the "unique value legends" familiar from well known desktop GIS systems
+     * 
+     * Parameters:
+     * renderIntent - {String} rendering intent to add the rules to
+     * property     - {String} values of feature attributes to create the
+     *                rules for
+     * symbolizers  - {Object} Hash of symbolizers, keyed by the desired
+     *                property values 
+     */
+    addUniqueValueRules: function(renderIntent, property, symbolizers) {
+        var rules = [];
+        for (var value in symbolizers) {
+            rules.push(new OpenLayers.Rule.Comparison({
+                type: OpenLayers.Rule.Comparison.EQUAL_TO,
+                property: property,
+                value: value,
+                symbolizer: symbolizers[value]}));
+        }
+        this.styles[renderIntent].addRules(rules);
+    },
 
     CLASS_NAME: "OpenLayers.StyleMap"
 });