Refactor filtered field code

lib/carto/tree/definition.js

@@ -216,10 +216,19 @@ tree.Definition.prototype.toJS = function(env) {
   var zoom = "(" + this.zoom + " & (1 << ctx.zoom))";
   var frame_offset = this.frame_offset;
   var _if = this.filters.toJS(env);
+  var filtered = _if !== '';
   var filters = [zoom];
-  if(_if) filters.push(_if);
+
-  if(frame_offset) filters.push('ctx["frame-offset"] === ' + frame_offset);
+  if(_if) {
+      filters.push(_if);
+  }
+
+  if(frame_offset){
+   filters.push('ctx["frame-offset"] === ' + frame_offset);
+  }
+
   _if = filters.join(" && ");
+  
   _.each(this.rules, function(rule) {
       if(rule instanceof tree.Rule) {
         shaderAttrs[rule.name] = shaderAttrs[rule.name] || [];
@@ -230,30 +239,16 @@ tree.Definition.prototype.toJS = function(env) {
         };
 
         if (_if) {
-          r.js = "if(" + _if + "){" + rule.value.toJS(env) + "}"
+          r.js = "if(" + _if + "){" + rule.value.toJS(env) + "}";
         } else {
           r.js = rule.value.toJS(env);
         }
 
         r.constant = rule.value.ev(env).is !== 'field';
-        var DEFAULT_FILTER = "(8388607 & (1 << ctx.zoom))";
+        r.filtered = filtered;
-        r.filtered = false;
-        if (_if && _if !== DEFAULT_FILTER){
-            r.filtered = true;
-        }
-
         shaderAttrs[rule.name].push(r);
       } else {
         throw new Error("Ruleset not supported");
-        //if (rule instanceof tree.Ruleset) {
-          //var sh = rule.toJS(env);
-          //for(var v in sh) {
-            //shaderAttrs[v] = shaderAttrs[v] || [];
-            //for(var attr in sh[v]) {
-              //shaderAttrs[v].push(sh[v][attr]);
-            //}
-          //}
-        //}
       }
   });
   return shaderAttrs;