public:
// cull parameters is a convenient way of passing a bunch
// of arguments through the culling functions without
// writing loads of code. Not all members are used for some cull checks
struct CullParams {
	int result_count_overall; // both trees
	int result_count; // this tree only
	int result_max;
	T **result_array;
	int *subindex_array;

	// nobody truly understands how masks are intended to work.
	uint32_t mask;
	uint32_t pairable_type;

	// optional components for different tests
	Vector3 point;
	BVH_ABB abb;
	typename BVH_ABB::ConvexHull hull;
	typename BVH_ABB::Segment segment;

	// when collision testing, non pairable moving items
	// only need to be tested against the pairable tree.
	// collisions with other non pairable items are irrelevant.
	bool test_pairable_only;
};

private:
void _cull_translate_hits(CullParams &p) {
	int num_hits = _cull_hits.size();
	int left = p.result_max - p.result_count_overall;

	if (num_hits > left)
		num_hits = left;

	int out_n = p.result_count_overall;

	for (int n = 0; n < num_hits; n++) {
		uint32_t ref_id = _cull_hits[n];

		const ItemExtra &ex = _extra[ref_id];
		p.result_array[out_n] = ex.userdata;

		if (p.subindex_array)
			p.subindex_array[out_n] = ex.subindex;

		out_n++;
	}

	p.result_count = num_hits;
	p.result_count_overall += num_hits;
}

public:
int cull_convex(CullParams &r_params, bool p_translate_hits = true) {

	_cull_hits.clear();
	r_params.result_count = 0;

	for (int n = 0; n < NUM_TREES; n++) {
		if (_root_node_id[n] == BVHCommon::INVALID)
			continue;

		_cull_convex_iterative(_root_node_id[n], r_params);
	}

	if (p_translate_hits)
		_cull_translate_hits(r_params);

	return r_params.result_count;
}

int cull_segment(CullParams &r_params, bool p_translate_hits = true) {
	_cull_hits.clear();
	r_params.result_count = 0;

	for (int n = 0; n < NUM_TREES; n++) {
		if (_root_node_id[n] == BVHCommon::INVALID)
			continue;

		_cull_segment_iterative(_root_node_id[n], r_params);
	}

	if (p_translate_hits)
		_cull_translate_hits(r_params);

	return r_params.result_count;
}

int cull_point(CullParams &r_params, bool p_translate_hits = true) {

	_cull_hits.clear();
	r_params.result_count = 0;

	for (int n = 0; n < NUM_TREES; n++) {
		if (_root_node_id[n] == BVHCommon::INVALID)
			continue;

		_cull_point_iterative(_root_node_id[n], r_params);
	}

	if (p_translate_hits)
		_cull_translate_hits(r_params);

	return r_params.result_count;
}

int cull_aabb(CullParams &r_params, bool p_translate_hits = true) {
	_cull_hits.clear();
	r_params.result_count = 0;

	for (int n = 0; n < NUM_TREES; n++) {
		if (_root_node_id[n] == BVHCommon::INVALID)
			continue;

		if ((n == 0) && r_params.test_pairable_only)
			continue;

		_cull_aabb_iterative(_root_node_id[n], r_params);
	}

	if (p_translate_hits)
		_cull_translate_hits(r_params);

	return r_params.result_count;
}

bool _cull_hits_full(const CullParams &p) {
	// instead of checking every hit, we can do a lazy check for this condition.
	// it isn't a problem if we write too much _cull_hits because they only the
	// result_max amount will be translated and outputted. But we might as
	// well stop our cull checks after the maximum has been reached.
	return (int)_cull_hits.size() >= p.result_max;
}

void _cull_hit(uint32_t p_ref_id, CullParams &p) {

	// take into account masks etc
	// this would be more efficient to do before plane checks,
	// but done here for ease to get started
	if (USE_PAIRS) {
		const ItemExtra &ex = _extra[p_ref_id];

		// double check this as a possible source of bugs in future.
		bool from_match_to = p.mask & ex.pairable_type;

		if (!from_match_to) {
			bool to_match_from = ex.pairable_mask & p.pairable_type;
			if (!to_match_from)
				return;
		}
	}

	_cull_hits.push_back(p_ref_id);
}

bool _cull_segment_iterative(uint32_t p_node_id, CullParams &r_params) {

	// our function parameters to keep on a stack
	struct CullSegParams {
		uint32_t node_id;
	};

	// most of the iterative functionality is contained in this helper class
	BVH_IterativeInfo<CullSegParams> ii;

	// alloca must allocate the stack from this function, it cannot be allocated in the
	// helper class
	ii.stack = (CullSegParams *)alloca(ii.get_alloca_stacksize());

	// seed the stack
	ii.get_first()->node_id = p_node_id;

	CullSegParams csp;

	// while there are still more nodes on the stack
	while (ii.pop(csp)) {

		TNode &tnode = _nodes[csp.node_id];

		if (tnode.is_leaf()) {

			// lazy check for hits full up condition
			if (_cull_hits_full(r_params)) {
				return false;
			}

			TLeaf &leaf = _node_get_leaf(tnode);

			// test children individually
			for (int n = 0; n < leaf.num_items; n++) {
				const BVH_ABB &aabb = leaf.get_aabb(n);

				if (aabb.intersects_segment(r_params.segment)) {
					uint32_t child_id = leaf.get_item_ref_id(n);

					// register hit
					_cull_hit(child_id, r_params);
				}
			}
		} else {
			// test children individually
			for (int n = 0; n < tnode.num_children; n++) {

				uint32_t child_id = tnode.children[n];
				const BVH_ABB &child_abb = _nodes[child_id].aabb;

				if (child_abb.intersects_segment(r_params.segment)) {

					// add to the stack
					CullSegParams *child = ii.request();
					child->node_id = child_id;
				}
			}
		}

	} // while more nodes to pop

	// true indicates results are not full
	return true;
}

bool _cull_point_iterative(uint32_t p_node_id, CullParams &r_params) {
	// our function parameters to keep on a stack
	struct CullPointParams {
		uint32_t node_id;
	};

	// most of the iterative functionality is contained in this helper class
	BVH_IterativeInfo<CullPointParams> ii;

	// alloca must allocate the stack from this function, it cannot be allocated in the
	// helper class
	ii.stack = (CullPointParams *)alloca(ii.get_alloca_stacksize());

	// seed the stack
	ii.get_first()->node_id = p_node_id;

	CullPointParams cpp;

	// while there are still more nodes on the stack
	while (ii.pop(cpp)) {

		TNode &tnode = _nodes[cpp.node_id];
		// no hit with this node?
		if (!tnode.aabb.intersects_point(r_params.point))
			continue;

		if (tnode.is_leaf()) {

			// lazy check for hits full up condition
			if (_cull_hits_full(r_params)) {
				return false;
			}

			TLeaf &leaf = _node_get_leaf(tnode);

			// test children individually
			for (int n = 0; n < leaf.num_items; n++) {

				if (leaf.get_aabb(n).intersects_point(r_params.point)) {
					uint32_t child_id = leaf.get_item_ref_id(n);

					// register hit
					_cull_hit(child_id, r_params);
				}
			}
		} else {
			// test children individually
			for (int n = 0; n < tnode.num_children; n++) {
				uint32_t child_id = tnode.children[n];

				// add to the stack
				CullPointParams *child = ii.request();
				child->node_id = child_id;
			}
		}

	} // while more nodes to pop

	// true indicates results are not full
	return true;
}

bool _cull_aabb_iterative(uint32_t p_node_id, CullParams &r_params, bool p_fully_within = false) {

	// our function parameters to keep on a stack
	struct CullAABBParams {
		uint32_t node_id;
		bool fully_within;
	};

	// most of the iterative functionality is contained in this helper class
	BVH_IterativeInfo<CullAABBParams> ii;

	// alloca must allocate the stack from this function, it cannot be allocated in the
	// helper class
	ii.stack = (CullAABBParams *)alloca(ii.get_alloca_stacksize());

	// seed the stack
	ii.get_first()->node_id = p_node_id;
	ii.get_first()->fully_within = p_fully_within;

	CullAABBParams cap;

	// while there are still more nodes on the stack
	while (ii.pop(cap)) {

		TNode &tnode = _nodes[cap.node_id];

		if (tnode.is_leaf()) {

			// lazy check for hits full up condition
			if (_cull_hits_full(r_params)) {
				return false;
			}

			TLeaf &leaf = _node_get_leaf(tnode);

			// if fully within we can just add all items
			// as long as they pass mask checks
			if (cap.fully_within) {
				for (int n = 0; n < leaf.num_items; n++) {
					uint32_t child_id = leaf.get_item_ref_id(n);

					// register hit
					_cull_hit(child_id, r_params);
				}
			} else {
				for (int n = 0; n < leaf.num_items; n++) {
					const BVH_ABB &aabb = leaf.get_aabb(n);

					if (aabb.intersects(r_params.abb)) {
						uint32_t child_id = leaf.get_item_ref_id(n);

						// register hit
						_cull_hit(child_id, r_params);
					}
				}
			} // not fully within
		} else {
			if (!cap.fully_within) {
				// test children individually
				for (int n = 0; n < tnode.num_children; n++) {

					uint32_t child_id = tnode.children[n];
					const BVH_ABB &child_abb = _nodes[child_id].aabb;

					if (child_abb.intersects(r_params.abb)) {
						// is the node totally within the aabb?
						bool fully_within = r_params.abb.is_other_within(child_abb);

						// add to the stack
						CullAABBParams *child = ii.request();

						// should always return valid child
						child->node_id = child_id;
						child->fully_within = fully_within;
					}
				}
			} else {
				for (int n = 0; n < tnode.num_children; n++) {
					uint32_t child_id = tnode.children[n];

					// add to the stack
					CullAABBParams *child = ii.request();

					// should always return valid child
					child->node_id = child_id;
					child->fully_within = true;
				}
			}
		}

	} // while more nodes to pop

	// true indicates results are not full
	return true;
}

// returns full up with results
bool _cull_convex_iterative(uint32_t p_node_id, CullParams &r_params, bool p_fully_within = false) {

	// our function parameters to keep on a stack
	struct CullConvexParams {
		uint32_t node_id;
		bool fully_within;
	};

	// most of the iterative functionality is contained in this helper class
	BVH_IterativeInfo<CullConvexParams> ii;

	// alloca must allocate the stack from this function, it cannot be allocated in the
	// helper class
	ii.stack = (CullConvexParams *)alloca(ii.get_alloca_stacksize());

	// seed the stack
	ii.get_first()->node_id = p_node_id;
	ii.get_first()->fully_within = p_fully_within;

	// preallocate these as a once off to be reused
	uint32_t max_planes = r_params.hull.num_planes;
	uint32_t *plane_ids = (uint32_t *)alloca(sizeof(uint32_t) * max_planes);

	CullConvexParams ccp;

	// while there are still more nodes on the stack
	while (ii.pop(ccp)) {
		const TNode &tnode = _nodes[ccp.node_id];

		if (!ccp.fully_within) {

			typename BVH_ABB::IntersectResult res = tnode.aabb.intersects_convex(r_params.hull);

			switch (res) {
				default: {
					continue; // miss, just move on to the next node in the stack
				} break;
				case BVH_ABB::IR_PARTIAL: {
				} break;
				case BVH_ABB::IR_FULL: {
					ccp.fully_within = true;
				} break;
			}

		} // if not fully within already

		if (tnode.is_leaf()) {

			// lazy check for hits full up condition
			if (_cull_hits_full(r_params)) {
				return false;
			}

			const TLeaf &leaf = _node_get_leaf(tnode);

			// if fully within, simply add all items to the result
			// (taking into account masks)
			if (ccp.fully_within) {

				for (int n = 0; n < leaf.num_items; n++) {

					uint32_t child_id = leaf.get_item_ref_id(n);

					// register hit
					_cull_hit(child_id, r_params);
				}

			} else {

				// we can either use a naive check of all the planes against the AABB,
				// or an optimized check, which finds in advance which of the planes can possibly
				// cut the AABB, and only tests those. This can be much faster.
#define BVH_CONVEX_CULL_OPTIMIZED
#ifdef BVH_CONVEX_CULL_OPTIMIZED
				// first find which planes cut the aabb
				uint32_t num_planes = tnode.aabb.find_cutting_planes(r_params.hull, plane_ids);
				BVH_ASSERT(num_planes <= max_planes);

//#define BVH_CONVEX_CULL_OPTIMIZED_RIGOR_CHECK
#ifdef BVH_CONVEX_CULL_OPTIMIZED_RIGOR_CHECK
				// rigorous check
				uint32_t results[MAX_ITEMS];
				uint32_t num_results = 0;
#endif

				// test children individually
				for (int n = 0; n < leaf.num_items; n++) {
					//const Item &item = leaf.get_item(n);
					const BVH_ABB &aabb = leaf.get_aabb(n);

					if (aabb.intersects_convex_optimized(r_params.hull, plane_ids, num_planes)) {
						uint32_t child_id = leaf.get_item_ref_id(n);

#ifdef BVH_CONVEX_CULL_OPTIMIZED_RIGOR_CHECK
						results[num_results++] = child_id;
#endif

						// register hit
						_cull_hit(child_id, r_params);
					}
				}

#ifdef BVH_CONVEX_CULL_OPTIMIZED_RIGOR_CHECK
				uint32_t test_count = 0;

				for (int n = 0; n < leaf.num_items; n++) {
					const BVH_ABB &aabb = leaf.get_aabb(n);

					if (aabb.intersects_convex_partial(r_params.hull)) {
						uint32_t child_id = leaf.get_item_ref_id(n);

						CRASH_COND(child_id != results[test_count++]);
						CRASH_COND(test_count > num_results);
					}
				}
#endif

#else
				// not BVH_CONVEX_CULL_OPTIMIZED
				// test children individually
				for (int n = 0; n < leaf.num_items; n++) {
					const BVH_ABB &aabb = leaf.get_aabb(n);

					if (aabb.intersects_convex_partial(r_params.hull)) {
						uint32_t child_id = leaf.get_item_ref_id(n);

						// full up with results? exit early, no point in further testing
						if (!_cull_hit(child_id, r_params))
							return false;
					}
				}
#endif // BVH_CONVEX_CULL_OPTIMIZED
			} // if not fully within
		} else {

			for (int n = 0; n < tnode.num_children; n++) {
				uint32_t child_id = tnode.children[n];

				// add to the stack
				CullConvexParams *child = ii.request();

				// should always return valid child
				child->node_id = child_id;
				child->fully_within = ccp.fully_within;
			}
		}

	} // while more nodes to pop

	// true indicates results are not full
	return true;
}