feat: Add support for laying out graphs horizontally

include/graaflib/io/dot.h

@@ -43,6 +43,8 @@ const auto default_edge_writer{
  * edge_id_t and a graph::edge_t and serialize it to a string. Default
  * implementations are provided for primitive numeric types.
  * @param path Path to the output dot file.
+ * @param horizontal If true, lays out the graph horizontally, otherwise lays it
+ * out vertically. Defaults to false.
  */
 template <typename V, typename E, graph_type T,
           typename VERTEX_WRITER_T = decltype(detail::default_vertex_writer<V>),
@@ -55,8 +57,9 @@ template <typename V, typename E, graph_type T,
 void to_dot(
     const graph<V, E, T>& graph, const std::filesystem::path& path,
     const VERTEX_WRITER_T& vertex_writer = detail::default_vertex_writer<V>,
-    const EDGE_WRITER_T& edge_writer = detail::default_edge_writer);
+    const EDGE_WRITER_T& edge_writer = detail::default_edge_writer,
+    bool horizontal = false);
 
 }  // namespace graaf::io
 
-#include "dot.tpp"
+#include "dot.tpp"

include/graaflib/io/dot.tpp

@@ -72,7 +72,7 @@ template <typename V, typename E, graph_type T, typename VERTEX_WRITER_T,
                                  const typename graph<V, E, T>::edge_t&>
 void to_dot(const graph<V, E, T>& graph, const std::filesystem::path& path,
             const VERTEX_WRITER_T& vertex_writer,
-            const EDGE_WRITER_T& edge_writer) {
+            const EDGE_WRITER_T& edge_writer, bool horizontal) {
   std::ofstream dot_file{path};
 
   const auto append_line{
@@ -81,6 +81,10 @@ void to_dot(const graph<V, E, T>& graph, const std::filesystem::path& path,
   // TODO(bluppes): replace with std::format once Clang supports it
   append_line(std::string(detail::graph_type_to_string(T)) + " {");
 
+  if (horizontal) {
+    append_line("rankdir=\"LR\";");
+  }
+
   for (const auto& [vertex_id, vertex] : graph.get_vertices()) {
     append_line("\t" + std::to_string(vertex_id) + " [" +
                 vertex_writer(vertex_id, vertex) + "];");

test/graaflib/io/dot_test.cpp

@@ -256,4 +256,40 @@ TEST(DotTest, DefaultWriters) {
                                            vertex_2)) != std::string::npos);
 }
 
-}  // namespace graaf::io
+TEST(DotTest, HorizontalGraph) {
+  // GIVEN
+  struct vertex_t {
+    int numeric_data{};
+    std::string string_data{};
+  };
+
+  struct edge_t {
+    int numeric_data{};
+    std::string string_data{};
+  };
+
+  const std::filesystem::path path{std::filesystem::temp_directory_path() /
+                                   "DotTest_HorizontalGraph.dot"};
+  directed_graph<vertex_t, edge_t> graph{};
+
+  const auto vertex_1{graph.add_vertex(vertex_t{10, "vertex 1"})};
+  const auto vertex_2{graph.add_vertex(vertex_t{20, "vertex 2"})};
+  graph.add_edge(vertex_1, vertex_2, edge_t{100, "edge 1"});
+
+  const auto vertex_writer{
+      [](vertex_id_t /*vertex_id*/, const vertex_t& vertex) {
+        return fmt::format("{}, {}", vertex.numeric_data, vertex.string_data);
+      }};
+  const auto edge_writer{[](const edge_id_t& /*edge_id*/, const auto& edge) {
+    return fmt::format("{}, {}", edge.numeric_data, edge.string_data);
+  }};
+
+  // WHEN
+  to_dot(graph, path, vertex_writer, edge_writer, true);
+
+  // THEN
+  const auto dot_content{read_to_string(path)};
+  ASSERT_TRUE(dot_content.find("rankdir=\"LR\"") != std::string::npos);
+}
+
+}  // namespace graaf::io