Little refactoring

lib/timeline/component/ItemSet.js

@@ -503,22 +503,23 @@ ItemSet.prototype.redraw = function() {
   this.lastVisibleInterval = visibleInterval;
   this.props.lastWidth = this.props.width;
 
+  var restack = this.stackDirty;
+  var firstGroup = this._firstGroup();
+  var firstMargin = {
+    item: margin.item,
+    axis: margin.axis
+  };
+  var nonFirstMargin = {
+    item: margin.item,
+    axis: margin.item.vertical / 2
+  };
+  var height = 0;
+  var minHeight = margin.axis + margin.item.vertical;
+
   // redraw the background group
   this.groups[BACKGROUND].redraw(range, nonFirstMargin, restack);
 
   // redraw all regular groups
-  var restack = this.stackDirty,
-      firstGroup = this._firstGroup(),
-      firstMargin = {
-        item: margin.item,
-        axis: margin.axis
-      },
-      nonFirstMargin = {
-        item: margin.item,
-        axis: margin.item.vertical / 2
-      },
-      height = 0,
-      minHeight = margin.axis + margin.item.vertical;
   util.forEach(this.groups, function (group) {
     var groupMargin = (group == firstGroup) ? firstMargin : nonFirstMargin;
     var groupResized = group.redraw(range, groupMargin, restack);
@@ -535,8 +536,6 @@ ItemSet.prototype.redraw = function() {
   this.props.width = frame.offsetWidth;
   this.props.height = height;
 
-  // reposition axis
-
   // reposition axis
   this.dom.axis.style.top = asSize((orientation == 'top') ?
       (this.body.domProps.top.height + this.body.domProps.border.top) :