made getItemRange respect visible graphgroups

lib/timeline/Graph2d.js

@@ -257,22 +257,20 @@ Graph2d.prototype.isGroupVisible = function(groupId) {
  *                                          When no maximum is found, max==null
  */
 Graph2d.prototype.getItemRange = function() {
+  var min = null;
+  var max = null;
+
   // calculate min from start filed
-  var dataset = this.itemsData.getDataSet(),
-    min = null,
-    max = null;
-
-  if (dataset) {
-    // calculate the minimum value of the field 'start'
-    var minItem = dataset.min('x');
-    min = minItem ? util.convert(minItem.x, 'Date').valueOf() : null;
-    // Note: we convert first to Date and then to number because else
-    // a conversion from ISODate to Number will fail
-
-    // calculate maximum value of fields 'start' and 'end'
-    var maxStartItem = dataset.max('x');
-    if (maxStartItem) {
-      max = util.convert(maxStartItem.x, 'Date').valueOf();
+  for (var groupId in this.linegraph.groups) {
+    if (this.linegraph.groups.hasOwnProperty(groupId)) {
+      if (this.linegraph.groups[groupId].visible == true) {
+        for (var i = 0; i < this.linegraph.groups[groupId].itemsData.length; i++) {
+          var item = this.linegraph.groups[groupId].itemsData[i];
+          var value = util.convert(item.x, 'Date').valueOf();
+          min = min == null ? value : min > value ? value : min;
+          max = max == null ? value : max < value ? value : max;
+        }
+      }
     }
   }