bool BVH4BuilderFast::splitSequential(BuildRecord& current, BuildRecord& leftChild, BuildRecord& rightChild)
 {
   /* mark as leaf if leaf threshold reached */
   if (current.items() <= QBVH_BUILDER_LEAF_ITEM_THRESHOLD) {
     current.createLeaf();
     return false;
   }
   
   /* calculate binning function */
   Mapping<16> mapping(current.bounds);
   
   /* binning of centroids */
   Binner<16> binner;
   binner.bin(prims,current.begin,current.end,mapping);
   
   /* find best split */
   Split split; 
   binner.best(split,mapping);
   
   /* if we cannot find a valid split, enforce an arbitrary split */
   if (unlikely(split.pos == -1)) split_fallback(prims,current,leftChild,rightChild);
   
   /* partitioning of items */
   else binner.partition(prims, current.begin, current.end, split, mapping, leftChild, rightChild);
   
   if (leftChild.items()  <= QBVH_BUILDER_LEAF_ITEM_THRESHOLD) leftChild.createLeaf();
   if (rightChild.items() <= QBVH_BUILDER_LEAF_ITEM_THRESHOLD) rightChild.createLeaf();	
   return true;
 }