Add 2D convex bodies interface & constexpr dimension retrieveing function

libs/cg/include/psemek/cg/body/body.hpp

@@ -12,7 +12,13 @@
 namespace psemek::cg
 {
 
-	/* The basic interface of a 3D body is
+	/* The basic interface of a 2D body is
+	 *   constexpr dimension(body) -> 2
+	 *   vertices(body) -> [point]
+	 *   edges(body) -> [(index, index)]
+	 *
+	 * The basic interface of a 3D body is
+	 *   constexpr dimension(body) -> 3
 	 *   vertices(body) -> [point]
 	 *   edges(body) -> [(index, index)]
 	 *   faces(body) -> [[index]]
@@ -24,7 +30,11 @@ namespace psemek::cg
 	 * However, it is possible that edges(body).size() != edge_directions(body).size,
 	 *   if there are many collinear edges.
 	 *
-	 * Minimal set of required functions:
+	 * Minimal set of required functions for 2D body:
+	 *   vertices
+	 *   edges
+	 *
+	 * Minimal set of required functions for 3D body:
 	 *   vertices
 	 *   edges
 	 *   faces/triangles

libs/cg/include/psemek/cg/body/box.hpp

@@ -13,6 +13,56 @@ namespace psemek::cg
 	template <typename T, std::size_t N>
 	box(geom::box<T, N>) -> box<T, N>;
 
+	template <typename T, std::size_t N>
+	constexpr std::size_t dimension(box<T, N> const &)
+	{
+		return N;
+	}
+
+	template <typename T>
+	struct box<T, 2>
+	{
+		box() = default;
+		box(geom::box<T, 2> const & b);
+
+		std::array<geom::point<T, 2>, 4> vertices;
+	};
+
+	template <typename T>
+	box<T, 2>::box(geom::box<T, 2> const & b)
+	{
+		for (std::size_t y = 0; y < 2; ++y)
+		{
+			for (std::size_t x = 0; x < 2; ++x)
+			{
+				std::size_t i = y * 2 + x;
+
+				vertices[i][0] = (x == 0) ? b[0].min : b[0].max;
+				vertices[i][1] = (y == 0) ? b[1].min : b[1].max;
+			}
+		}
+	}
+
+	template <typename T>
+	auto const & vertices(box<T, 2> const & b)
+	{
+		return b.vertices;
+	}
+
+	template <typename T>
+	auto const & edges(box<T, 2> const &)
+	{
+		static const std::array<geom::segment<std::uint8_t>, 12> result =
+		{{
+			{ 0b00, 0b01 },
+			{ 0b01, 0b11 },
+			{ 0b11, 0b10 },
+			{ 0b10, 0b00 },
+		}};
+
+		return result;
+	}
+
 	template <typename T>
 	struct box<T, 3>
 	{

libs/cg/include/psemek/cg/body/frustum.hpp

@@ -24,6 +24,12 @@ namespace psemek::cg
 		std::array<geom::point<T, 3>, 8> vertices;
 	};
 
+	template <typename T, std::size_t N>
+	constexpr std::size_t dimension(frustum<T, N> const &)
+	{
+		return N;
+	}
+
 	template <typename T>
 	frustum<T, 3>::frustum(geom::matrix<T, 4, 4> const & m)
 	{

libs/cg/include/psemek/cg/body/icosahedron.hpp

@@ -14,6 +14,12 @@ namespace psemek::cg
 		std::array<geom::point<T, 3>, 12> vertices;
 	};
 
+	template <typename T>
+	constexpr std::size_t dimension(icosahedron<T> const &)
+	{
+		return 3;
+	}
+
 	template <typename T>
 	icosahedron<T>::icosahedron(geom::point<T, 3> const & origin, T radius)
 	{

libs/cg/include/psemek/cg/body/prism.hpp

@@ -15,6 +15,12 @@ namespace psemek::cg
 		std::array<geom::vector<T, 3>, 4> edge_directions;
 	};
 
+	template <typename T>
+	constexpr std::size_t dimension(triangular_prism<T> const &)
+	{
+		return 3;
+	}
+
 	template <typename T>
 	triangular_prism<T>::triangular_prism(geom::triangle<geom::point<T, 3>> const & t, geom::vector<T, 3> const & d)
 	{