Added option to center items horizontally

When the layout mode fitRows is set and the option fitRows.centered is set to "true", items not spanning the whole container will be centered within the container. I tried adding this functionality to the masonry layoutmode, but failed miserably. In retrospect this was pretty easy, but it took me quite some time to understand how isotope and it's layout modes work internally.

I've done some tests and am pretty sure it works, but it is possible I missed something. Hope this helps :)

js/layout-modes/fit-rows.js

@@ -7,7 +7,7 @@
   /* jshint strict: false */ /*globals define, module, require */
   if ( typeof define == 'function' && define.amd ) {
     // AMD
-    define( [
+    define( 'isotope/layout-modes/fit-rows',[
         '../layout-mode'
       ],
       factory );
@@ -35,6 +35,12 @@ proto._resetLayout = function() {
   this.y = 0;
   this.maxY = 0;
   this._getMeasurement( 'gutter', 'outerWidth' );
+
+  if(this.options.centered) {
+	  this.rowCount = 0;
+	  this.positioned = 0;
+	  this.numItems = this.isotope.filteredItems.length;
+  }
 };
 
 proto._getItemLayoutPosition = function( item ) {
@@ -43,11 +49,27 @@ proto._getItemLayoutPosition = function( item ) {
   var itemWidth = item.size.outerWidth + this.gutter;
   // if this element cannot fit in the current row
   var containerWidth = this.isotope.size.innerWidth + this.gutter;
-  if ( this.x !== 0 && itemWidth + this.x > containerWidth ) {
+   // items per row
+
+ if ( this.x !== 0 && itemWidth + this.x > containerWidth ) {
     this.x = 0;
     this.y = this.maxY;
   } 
 
+  if(this.options.centered) {
+	  var itemsPerRow = Math.round(containerWidth / itemWidth);
+	  var remainder = this.numItems % itemsPerRow;
+	  var rows = Math.ceil(this.numItems / itemsPerRow);
+	  var itemsLeftToPosition = this.numItems - this.positioned - 1;
+	  if(this.x === 0) {
+		  this.rowCount++;
+		  if(remainder > 0 && rows === this.rowCount) {
+			var takenSpace = itemWidth * itemsLeftToPosition;
+			this.x = Math.round(( containerWidth / 2) - ( takenSpace / 2) - (itemWidth / 2));
+		  }
+	  }
+  } 
+
   var position = {
     x: this.x,
     y: this.y
@@ -56,6 +78,10 @@ proto._getItemLayoutPosition = function( item ) {
   this.maxY = Math.max( this.maxY, this.y + item.size.outerHeight );
   this.x += itemWidth;
   
+  if(this.options.centered) {
+	  this.positioned++;
+  }
+  
   return position;
 };