//---- initialisation
Stack.Push(kDTree.Root);
//---- while there are some nodes in the stack or the query queue
while (!Stack.Empty() $||$ !QueryQueue.Empty()) {
  //---- PART 1: processing finished occlusion queries
  while (!QueryQueue.Empty() &&
	 (ResultAvailable(QueryQueue.Front()) $||$ Stack.Empty())) {
    if (!ResultAvailable(QueryQueue.Front())) {
      //--- result is not available and the stack is empty
      //--- check if we can do some conservative decision
      N = QueryQueue.GetLeastCostNode();
      if (N.renderingCost < MaxRenderCost) {
	RenderSubtree(N);
	QueryQueue.DequeLeastCostNode();
	//-- we do not change N's visibility classfication -
	//-- N remains in the cut for the next frame
      } else
	//-- wait for the availability of the result
	while (!QueryQueue.ResultAvailable) Wait();
    } else {
      N = QueryQueue.Dequeue();
      //-- check the result of the query
      if ( N.visiblePixels $>$ VisibilityThreshold )  {
	N.visibility = VISIBLE;
	if (IsLeaf(N))
	  Render(N);
	else {
	  //-- pull down
	  Stack.Push(FarChild(N)); Stack.Push(CloseChild(N));
	}
      } else {
	N.visibility = INVISIBLE;
	//-- pull up
	PullUpInvisibility(N);
      }
    }
  }
  
  //---- PART 2: kd-tree traversal
  if (!Stack.Empty()) {
    N = Stack.Pop();
    N.lastVisited = frameID;
    if (InsideViewFrustum(N)) {
      //-- skip testing of all nodes above the cut
      if (!IsAboveTheCut(N)) {
	IssueOcclustionQuery(N); QueryQueue.Enqueue(N);
	if (WasVisible(N) $&&$ IsLeaf(N))
	  Render(N);
	else {
	  //-- go down the kD-tree
	  Stack.Push(FarChild(N)); Stack.Push(CloseChild(N)); 
	}
      }
    }
  }
}