feat: align_layout()

src/_igraph/graphobject.c

@@ -8188,14 +8188,15 @@ PyObject *igraphmodule_Graph_layout_kamada_kawai(igraphmodule_GraphObject *
  return NULL;
  }
 
- if (dim == 2)
+ if (dim == 2) {
  ret = igraph_layout_kamada_kawai
  (&self->g, &m, use_seed, maxiter, epsilon, kkconst,
  weights, /*bounds*/ minx, maxx, miny, maxy);
- else
+  } else {
  ret = igraph_layout_kamada_kawai_3d
  (&self->g, &m, use_seed, maxiter, epsilon, kkconst,
  weights, /*bounds*/ minx, maxx, miny, maxy, minz, maxz);
+ }
 
  DESTROY_VECTORS;
 
@@ -8207,6 +8208,19 @@ PyObject *igraphmodule_Graph_layout_kamada_kawai(igraphmodule_GraphObject *
  return NULL;
  }
 
+ /* Align layout, but only if no bounding box was specified. */
+ if (minx == NULL && maxx == NULL &&
+ miny == NULL && maxy == NULL &&
+ minz == NULL && maxz == NULL &&
+ igraph_vcount(&self->g) <= 1000) {
+ ret = igraph_layout_align(&self->g, &m);
+ if (ret) {
+ igraph_matrix_destroy(&m);
+ igraphmodule_handle_igraph_error();
+ return NULL;
+ }
+ }
+
  result_o = igraphmodule_matrix_t_to_PyList(&m, IGRAPHMODULE_TYPE_FLOAT);
  igraph_matrix_destroy(&m);
  return (PyObject *) result_o;
@@ -8298,6 +8312,16 @@ PyObject* igraphmodule_Graph_layout_davidson_harel(igraphmodule_GraphObject *sel
  return NULL;
  }
 
+ /* Align layout */
+ if (igraph_vcount(&self->g)) {
+ retval = igraph_layout_align(&self->g, &m);
+ if (retval) {
+ igraph_matrix_destroy(&m);
+ igraphmodule_handle_igraph_error();
+ return NULL;
+ }
+ }
+
  result_o = igraphmodule_matrix_t_to_PyList(&m, IGRAPHMODULE_TYPE_FLOAT);
  igraph_matrix_destroy(&m);
  return (PyObject *) result_o;
@@ -8520,6 +8544,19 @@ PyObject
  return NULL;
  }
 
+ /* Align layout, but only if no bounding box was specified. */
+ if (minx == NULL && maxx == NULL &&
+ miny == NULL && maxy == NULL &&
+ minz == NULL && maxz == NULL &&
+ igraph_vcount(&self->g) <= 1000) {
+ ret = igraph_layout_align(&self->g, &m);
+ if (ret) {
+ igraph_matrix_destroy(&m);
+ igraphmodule_handle_igraph_error();
+ return NULL;
+ }
+ }
+
 #undef DESTROY_VECTORS
 
  result_o = igraphmodule_matrix_t_to_PyList(&m, IGRAPHMODULE_TYPE_FLOAT);
@@ -8574,6 +8611,15 @@ PyObject *igraphmodule_Graph_layout_graphopt(igraphmodule_GraphObject *self,
  return NULL;
  }
 
+ /* Align layout */
+ if (igraph_vcount(&self->g) <= 1000) {
+ if (igraph_layout_align(&self->g, &m)) {
+ igraph_matrix_destroy(&m);
+ igraphmodule_handle_igraph_error();
+ return NULL;
+ }
+ }
+
  result_o = igraphmodule_matrix_t_to_PyList(&m, IGRAPHMODULE_TYPE_FLOAT);
  igraph_matrix_destroy(&m);
  return (PyObject *) result_o;
@@ -8632,6 +8678,15 @@ PyObject *igraphmodule_Graph_layout_lgl(igraphmodule_GraphObject * self,
  return NULL;
  }
 
+ /* Align layout */
+ if (igraph_vcount(&self->g) <= 1000) {
+ if (igraph_layout_align(&self->g, &m)) {
+ igraph_matrix_destroy(&m);
+ igraphmodule_handle_igraph_error();
+ return NULL;
+ }
+ }
+
  result_o = igraphmodule_matrix_t_to_PyList(&m, IGRAPHMODULE_TYPE_FLOAT);
  igraph_matrix_destroy(&m);
  return (PyObject *) result_o;
@@ -8697,6 +8752,15 @@ PyObject *igraphmodule_Graph_layout_mds(igraphmodule_GraphObject * self,
  igraph_matrix_destroy(dist); free(dist);
  }
 
+ /* Align layout */
+ if (igraph_vcount(&self->g) <= 1000) {
+ if (igraph_layout_align(&self->g, &m)) {
+ igraph_matrix_destroy(&m);
+ igraphmodule_handle_igraph_error();
+ return NULL;
+ }
+ }
+
  result_o = igraphmodule_matrix_t_to_PyList(&m, IGRAPHMODULE_TYPE_FLOAT);
  igraph_matrix_destroy(&m);
  return (PyObject *) result_o;

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.

tests/test_layouts.py

@@ -1,6 +1,6 @@
 import unittest
 from math import hypot
-from igraph import Graph, Layout, BoundingBox, InternalError
+from igraph import Graph, Layout, BoundingBox, InternalError, align_layout
 from igraph import umap_compute_weights
 
 
@@ -452,6 +452,13 @@ def testDRL(self):
  lo = g.layout("drl")
  self.assertTrue(isinstance(lo, Layout))
 
+ def testAlign(self):
+ g = Graph.Ring(3, circular=False)
+ lo = Layout([[1,1], [2,2], [3,3]])
+ lo = align_layout(g, lo)
+ self.assertTrue(isinstance(lo, Layout))
+ self.assertTrue(all(abs(lo[i][1]) < 1e-10 for i in range(3)))
+
 
 def suite():
  layout_suite = unittest.defaultTestLoader.loadTestsFromTestCase(LayoutTests)