Add some meshing utilities

libs/geom/include/psemek/geom/mesh.hpp

@@ -51,6 +51,78 @@ namespace psemek::geom
 		return result;
 	}
 
+	template <typename Index = std::uint32_t, typename T>
+	std::vector<triangle<Index>> faces(box<T, 2> const &)
+	{
+		std::vector<triangle<Index>> result;
+		result.push_back({0, 1, 2});
+		result.push_back({2, 1, 3});
+		return result;
+	}
+
+	template <typename Index = std::uint32_t, typename T>
+	std::vector<triangle<Index>> faces(box<T, 3> const &)
+	{
+		std::vector<triangle<Index>> result;
+		// -Z
+		result.push_back({0, 2, 1});
+		result.push_back({1, 2, 3});
+		// +Z
+		result.push_back({4, 5, 6});
+		result.push_back({6, 5, 7});
+		// -Y
+		result.push_back({0, 1, 4});
+		result.push_back({4, 1, 5});
+		// +Y
+		result.push_back({2, 6, 3});
+		result.push_back({6, 7, 3});
+		// -X
+		result.push_back({0, 4, 2});
+		result.push_back({2, 4, 6});
+		// +X
+		result.push_back({1, 3, 5});
+		result.push_back({3, 7, 5});
+		return result;
+	}
+
+	template <typename Vertex, typename Index, std::size_t N>
+	std::vector<simplex<Vertex, N>> deindex(std::vector<Vertex> const & vertices, std::vector<simplex<Index, N>> const & simplices)
+	{
+		std::vector<simplex<Vertex, N>> result;
+		result.reserve(simplices.size());
+		for (auto const & s : simplices)
+		{
+			result.emplace_back();
+			for (std::size_t i = 0; i <= N; ++i)
+				result.back()[i] = vertices[s[i]];
+		}
+		return result;
+	}
+
+	namespace detail
+	{
+
+		template <typename F, typename G, std::size_t ... I>
+		auto map_index_sequence(F && f, G && g, std::index_sequence<I...>)
+		{
+			return f(g(I)...);
+		}
+
+	}
+
+	template <typename T, std::size_t N, typename Index>
+	std::vector<vector<T, N + 1>> flat_normals(std::vector<point<T, N + 1>> const & vertices, std::vector<simplex<Index, N>> const & simplices)
+	{
+		std::vector<vector<T, N + 1>> result;
+		result.reserve(simplices.size());
+		for (auto const & s : simplices)
+		{
+			auto const n = detail::map_index_sequence([&](auto const & ... vs){ return normal(vs...); }, [&](std::size_t i){ return vertices[s[i]]; }, std::make_index_sequence<N + 1>{});
+			result.push_back(n);
+		}
+		return result;
+	}
+
 	template <typename Index = std::uint32_t, typename Vertex>
 	std::vector<triangle<Index>> triangulate_convex(std::vector<Vertex> const & v)
 	{