feat: align_layout()

Author: szhorvat

src/_igraph/igraphmodule.c

@@ -227,6 +227,38 @@ PyObject* igraphmodule_set_status_handler(PyObject* self, PyObject* o) {
   Py_RETURN_NONE;
 }
 
+PyObject* igraphmodule_align_layout(PyObject* self, PyObject* args, PyObject* kwds) {
+  static char* kwlist[] = {"graph", "layout", NULL};
+  PyObject *graph_o, *layout_o;
+  PyObject *res;
+  igraph_t *graph;
+  igraph_matrix_t layout;
+
+  if (!PyArg_ParseTupleAndKeywords(args, kwds, "OO", kwlist, &graph_o, &layout_o)) {
+    return NULL;
+  }
+
+  if (igraphmodule_PyObject_to_igraph_t(graph_o, &graph)) {
+    return NULL;
+  }
+
+  if (igraphmodule_PyObject_to_matrix_t(layout_o, &layout, "layout")) {
+    return NULL;
+  }
+
+  if (igraph_layout_align(graph, &layout)) {
+    igraphmodule_handle_igraph_error();
+    igraph_matrix_destroy(&layout);
+    return NULL;
+  }
+
+  res = igraphmodule_matrix_t_to_PyList(&layout, IGRAPHMODULE_TYPE_FLOAT);
+
+  igraph_matrix_destroy(&layout);
+
+  return res;
+}
+
 PyObject* igraphmodule_convex_hull(PyObject* self, PyObject* args, PyObject* kwds) {
   static char* kwlist[] = {"vs", "coords", NULL};
   PyObject *vs, *o, *o1 = 0, *o2 = 0, *o1_float, *o2_float, *coords = Py_False;
@@ -790,6 +822,10 @@ static PyMethodDef igraphmodule_methods[] =
     METH_VARARGS | METH_KEYWORDS,
     "_power_law_fit(data, xmin=-1, force_continuous=False, p_precision=0.01)\n--\n\n"
   },
+  {"_align_layout", (PyCFunction)igraphmodule_align_layout,
+    METH_VARARGS | METH_KEYWORDS,
+    "_align_layout(graph, layout)\n--\n\n"
+  },
   {"convex_hull", (PyCFunction)igraphmodule_convex_hull,
     METH_VARARGS | METH_KEYWORDS,
     "convex_hull(vs, coords=False)\n--\n\n"

src/igraph/__init__.py

@@ -227,6 +227,7 @@
 from igraph.io.images import _write_graph_to_svg
 from igraph.layout import (
     Layout,
+    align_layout,
     _layout,
     _layout_auto,
     _layout_sugiyama,

src/igraph/layout.py

@@ -16,6 +16,7 @@
 
 __all__ = (
     "Layout",
+    "align_layout",
     "_layout",
     "_layout_auto",
     "_layout_sugiyama",
@@ -534,6 +535,27 @@ def _layout(graph, layout=None, *args, **kwds):
     return layout
 
 
+def align_layout(graph, layout):
+    """Aligns a graph layout with the coordinate axes
+
+    This function centers a vertex layout on the coordinate system origin and
+    rotates the layout to achieve a visually pleasing alignment with the coordinate
+    axes. Doing this is particularly useful with force-directed layouts such as
+    L{Graph.layout_fruchterman_reingold}. Layouts in arbitrary dimensional spaces
+    are supported.
+
+    @param graph: the graph that the layout is associated with.
+    @param layout: the L{Layout} object containing the vertex coordinates
+      to align.
+    @return: a new aligned L{Layout} object.
+    """
+    from igraph._igraph import _align_layout
+
+    if not isinstance(layout, Layout):
+        layout = Layout(layout)
+
+    return Layout(_align_layout(graph, layout.coords))
+
 def _layout_auto(graph, *args, **kwds):
     """Chooses and runs a suitable layout function based on simple
     topological properties of the graph.