Add resolve_duplicated_faces binding; fix boundary_loop/vertex_components docs

src/boundary_loop.cpp

@@ -16,7 +16,7 @@ namespace pyigl
     igl::boundary_loop(F, loops);
     return loops;
   }
-  // Wrapper for boundary_loop that returns all loops as a vector of vectors
+  // Wrapper for boundary_loop that returns only the longest loop as a vector
   auto boundary_loop(const nb::DRef<const Eigen::MatrixXI> &F)
   {
     Eigen::VectorXI longest;

src/resolve_duplicated_faces.cpp

@@ -0,0 +1,45 @@
+#include "default_types.h"
+#include <igl/resolve_duplicated_faces.h>
+#include <nanobind/nanobind.h>
+#include <nanobind/eigen/dense.h>
+#include <nanobind/stl/tuple.h>
+#include <tuple>
+
+namespace nb = nanobind;
+using namespace nb::literals;
+
+namespace pyigl
+{
+  auto resolve_duplicated_faces(
+    const nb::DRef<const Eigen::MatrixXI> &F1)
+  {
+    // resolve_duplicated_faces reuses the input's Derived type for internal
+    // plain objects, so it needs a concrete matrix rather than an Eigen::Ref.
+    const Eigen::MatrixXI F1c = F1;
+    Eigen::MatrixXI F2;
+    Eigen::VectorXI J;
+    igl::resolve_duplicated_faces(F1c, F2, J);
+    return std::make_tuple(F2, J);
+  }
+}
+
+void bind_resolve_duplicated_faces(nb::module_ &m)
+{
+  m.def("resolve_duplicated_faces", &pyigl::resolve_duplicated_faces, "F1"_a,
+    R"(Resolve duplicated faces according to the following rules per unique face:
+
+1. If the number of positively oriented faces equals the number of negatively
+   oriented faces, remove all duplicated faces at this triangle.
+2. If the number of positively oriented faces equals the number of negatively
+   oriented faces plus 1, keep one of the positively oriented faces.
+3. If the number of positively oriented faces equals the number of negatively
+   oriented faces minus 1, keep one of the negatively oriented faces.
+4. If the number of positively oriented faces differs from the number of
+   negatively oriented faces by more than 1, the mesh is not orientable at that
+   triangle and all of its copies are dropped.
+
+@param[in] F1  #F1 by 3 array of input faces
+@return Tuple (F2, J) where
+  F2  #F2 by 3 array of output faces without duplicated faces
+  J   #F2 list of indices into F1)");
+}

src/vertex_components.cpp

@@ -21,13 +21,13 @@ namespace pyigl
 // Bind the wrappers to the Python module
 void bind_vertex_components(nb::module_ &m)
 {
-  // Binding for vertex_components with adjacency matrix and counts
+  // Binding for vertex_components from a mesh's face list
   m.def(
     "vertex_components",
     &pyigl::vertex_components,
     "F"_a,
-    R"(Compute the connected components of a graph using an adjacency matrix, returning component IDs and counts.
+    R"(Compute the connected component ids of each vertex of a mesh given its faces.
 
-@param[in] F       Matrix of triangle indices
-@return            Vector C of component IDs per vertex)");
+@param[in] F  #F by 3 matrix of triangle (face) indices
+@return       Vector C of per-vertex connected-component ids)");
 }

tests/test_all.py

@@ -1754,3 +1754,40 @@ def test_predicates_spline_winding_number():
     assert W.shape == (2,)
     assert np.isclose(abs(W[0]), 1.0, atol=1e-9)
     assert np.isclose(W[1], 0.0, atol=1e-9)
+
+
+# --------------------------------------------------------------------------
+# resolve_duplicated_faces
+# --------------------------------------------------------------------------
+
+def test_resolve_duplicated_faces():
+    # A mesh with no duplicated faces is returned unchanged.
+    F = np.array([[0, 1, 2], [2, 3, 0]], dtype=np.int64)
+    F2, J = igl.resolve_duplicated_faces(F)
+    assert np.array_equal(F2, F)
+    assert list(J.ravel()) == [0, 1]
+
+    # A pair of oppositely-oriented copies of the same face cancels out, while a
+    # distinct unique face is kept (rule 1).
+    F = np.array([[0, 1, 2],   # unique face, kept
+                  [2, 1, 3],   # face B, +
+                  [3, 1, 2]],  # face B reversed, - -> cancels with the above
+                 dtype=np.int64)
+    F2, J = igl.resolve_duplicated_faces(F)
+    assert set(map(tuple, F2.tolist())) == {(0, 1, 2)}
+    assert list(J.ravel()) == [0]
+
+    # Two positive copies and one negative copy: keep a single positive face
+    # (rule 2). J indexes back into the input.
+    F = np.array([[0, 1, 2], [0, 1, 2], [1, 0, 2]], dtype=np.int64)
+    F2, J = igl.resolve_duplicated_faces(F)
+    assert F2.shape[0] == 1
+    assert tuple(F2[0]) == (0, 1, 2)
+    assert F.shape[1] == F2.shape[1]
+    assert np.array_equal(F[J.ravel()], F2)
+
+    # Non-orientable triangle (three identical copies, |pos-neg| > 1): all of its
+    # copies are dropped, unrelated faces survive (rule 4).
+    F = np.array([[0, 1, 2], [0, 1, 2], [0, 1, 2], [3, 4, 5]], dtype=np.int64)
+    F2, J = igl.resolve_duplicated_faces(F)
+    assert set(map(tuple, F2.tolist())) == {(3, 4, 5)}