From 94cb475ecc3152ac2e979e5a3c534d71ef79c589 Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Wed, 29 Jun 2022 12:13:10 +0300
Subject: [PATCH] Add generic ndtree implementation

---
 libs/cg/include/psemek/cg/ndtree.hpp | 227 +++++++++++++++++++++++++++
 1 file changed, 227 insertions(+)
 create mode 100644 libs/cg/include/psemek/cg/ndtree.hpp

diff --git a/libs/cg/include/psemek/cg/ndtree.hpp b/libs/cg/include/psemek/cg/ndtree.hpp
new file mode 100644
index 00000000..30dc8f77
--- /dev/null
+++ b/libs/cg/include/psemek/cg/ndtree.hpp
@@ -0,0 +1,227 @@
+#pragma once
+
+#include <psemek/geom/point.hpp>
+#include <psemek/geom/box.hpp>
+#include <psemek/geom/contains.hpp>
+
+#include <memory>
+#include <optional>
+
+namespace psemek::cg
+{
+
+	template <typename T, std::size_t N, typename Data>
+	struct ndtree;
+
+	template <typename T, typename Data>
+	using quadtree = ndtree<T, 2, Data>;
+
+	template <typename T, typename Data>
+	using octree = ndtree<T, 3, Data>;
+
+	template <typename T, std::size_t N, typename Data>
+	struct ndtree
+	{
+	public:
+		using point_type = geom::point<T, N>;
+		using box_type = geom::box<T, N>;
+
+		struct value_type
+		{
+			point_type point;
+			Data data;
+
+			template <typename A, typename B>
+			value_type(A && point, B && data)
+				: point(std::forward<A>(point))
+				, data(std::forward<B>(data))
+			{}
+		};
+
+		struct node;
+
+		using node_ptr = std::unique_ptr<node>;
+		using node_ref = node *;
+
+		struct node
+		{
+			node_ptr children[1 << N];
+
+			std::optional<value_type> value;
+
+			node() = default;
+
+			template <typename A, typename B>
+			node(A && point, B && data)
+				: value(std::in_place, std::forward<A>(point), std::forward<B>(data))
+			{}
+
+			bool leaf() const
+			{
+				return std::all_of(std::begin(children), std::end(children), [](node_ptr const & p){ return !static_cast<bool>(p); });
+			}
+
+			bool full() const
+			{
+				return std::all_of(std::begin(children), std::end(children), [](node_ptr const & p){ return static_cast<bool>(p); });
+			}
+		};
+
+		template <typename A, typename B>
+		std::pair<node_ref, bool> insert(A && point, B && data)
+		{
+			if (!root)
+			{
+				root = std::make_unique<node>(std::forward<A>(point), std::forward<B>(data));
+				for (std::size_t d = 0; d < N; ++d)
+				{
+					root_bbox[d].min = root->value->point[d];
+					root_bbox[d].max = root->value->point[d] + T{1};
+				}
+
+				return {root.get(), true};
+			}
+
+			if (!geom::half_open_contains(root_bbox, point))
+			{
+				while (!geom::half_open_contains(root_bbox, point))
+					extend_root(point);
+			}
+
+			node * current_node = root.get();
+			box_type current_bbox = root_bbox;
+
+			while (true)
+			{
+				if (current_node->leaf())
+				{
+					if (current_node->value)
+					{
+						if (current_node->value->point == point)
+						{
+							return {current_node, false};
+						}
+						else
+						{
+							split(current_node, current_bbox);
+							assert(!current_node->value);
+						}
+					}
+					else
+					{
+						current_node->value.emplace(std::forward<A>(point), std::forward<B>(data));
+						return {current_node, true};
+					}
+				}
+
+				std::size_t index = 0;
+				for (std::size_t d = 0; d < N; ++d)
+				{
+					auto const c = current_bbox[d].center();
+					if (point[d] < c)
+					{
+						current_bbox[d].max = c;
+					}
+					else
+					{
+						index |= (1 << d);
+						current_bbox[d].min = c;
+					}
+				}
+
+				auto & child = current_node->children[index];
+
+				if (!child)
+				{
+					child = std::make_unique<node>(std::forward<A>(point), std::forward<B>(data));
+					return {child.get(), true};
+				}
+
+				current_node = child.get();
+			}
+		}
+
+		template <typename Visitor>
+		void traverse(Visitor && visitor) const
+		{
+			if (!root) return;
+			traverse_impl(std::forward<Visitor>(visitor), root.get(), root_bbox);
+		}
+
+		template <typename Visitor>
+		void traverse(Visitor && visitor, node_ref current_node, box_type const & bbox) const
+		{
+			if (!current_node) return;
+			traverse_impl(std::forward<Visitor>(visitor), current_node, bbox);
+		}
+
+	private:
+
+		node_ptr root;
+		geom::box<T, N> root_bbox;
+
+		void extend_root(point_type const & point)
+		{
+			std::size_t index_in_new_root = 0;
+			for (std::size_t d = 0; d < N; ++d)
+			{
+				if (point[d] >= root_bbox[d].min)
+					root_bbox[d].max += root_bbox[d].length();
+				else
+				{
+					root_bbox[d].min -= root_bbox[d].length();
+					index_in_new_root |= (1 << d);
+				}
+			}
+
+			auto new_root = std::make_unique<node>();
+			new_root->children[index_in_new_root] = std::move(root);
+			root = std::move(new_root);
+		}
+
+		static void split(node * n, box_type const & bbox)
+		{
+			assert(n->value);
+
+			std::size_t index_in_parent = 0;
+			for (std::size_t d = 0; d < N; ++d)
+			{
+				if (n->value->point[d] >= bbox[d].center())
+					index_in_parent |= (1 << d);
+			}
+
+			auto & child = n->children[index_in_parent];
+			child = std::make_unique<node>(n->value->point, std::move(n->value->data));
+			n->value = std::nullopt;
+		}
+
+		template <typename Visitor>
+		static void traverse_impl(Visitor && visitor, node * current_node, box_type const & box)
+		{
+			std::size_t children_count = 0;
+			for (std::size_t i = 0; i < (1 << N); ++i)
+				if (current_node->children[i])
+					++children_count;
+
+			if (visitor(*current_node, box))
+			{
+				for (std::size_t i = 0; i < (1 << N); ++i)
+				{
+					if (!current_node->children[i]) continue;
+
+					box_type child_box;
+					for (std::size_t d = 0; d < N; ++d)
+					{
+						auto const c = box[d].center();
+						if (i & (1 << d))
+							child_box[d] = {c, box[d].max};
+						else
+							child_box[d] = {box[d].min, c};
+					}
+					traverse_impl(visitor, current_node->children[i].get(), child_box);
+				}
+			}
+		}
+	};
+
+}