Some reverting and small fix in filter.py

Author: Jarvis2001

openmc/filter.py

@@ -37,7 +37,6 @@
 )
 
 
-
 class FilterMeta(ABCMeta):
     """Metaclass for filters that ensures class names are appropriate."""
 
@@ -1113,12 +1112,20 @@ def from_volumes(cls, mesh: openmc.MeshBase, volumes: openmc.MeshMaterialVolumes
             A new MeshMaterialFilter instance
 
         """
-        # Get flat arrays of material IDs and element indices
-        mat_ids = volumes._materials[volumes._materials > -1]
-        elems, _ = np.where(volumes._materials > -1)
-
-        # Stack them into a 2D array of (element, material) pairs
-        bins = np.column_stack((elems, mat_ids))
+        # Build bins sorted by volume ascending (mat ID ascending as tiebreaker)
+        # so the bin ordering is deterministic regardless of the ray-traversal
+        # order stored in the raw _materials array.
+        bins = []
+        for i in range(volumes.num_elements):
+            entries = volumes.by_element(i)
+            # sort by (volume asc, mat_id asc), excluding void (None)
+            entries = sorted(
+                ((mat_id, vol)
+                 for mat_id, vol in entries if mat_id is not None),
+                key=lambda t: (t[1], t[0])
+            )
+            for mat_id, _ in entries:
+                bins.append((i, mat_id))
         return cls(mesh, bins)
 
     def __hash__(self):
@@ -1861,7 +1868,7 @@ def __init__(self, particles, energies=None, filter_id=None):
     def __repr__(self):
         string = type(self).__name__ + '\n'
         string += '{: <16}=\t{}\n'.format('\tParticles',
-            [str(p) for p in self.particles])
+                                          [str(p) for p in self.particles])
         if self.energies is not None:
             string += '{: <16}=\t{}\n'.format('\tEnergies', self.energies)
         string += '{: <16}=\t{}\n'.format('\tID', self.id)
@@ -2171,7 +2178,7 @@ def paths(self):
         if self._paths is None:
             if not hasattr(self, '_geometry'):
                 raise ValueError(
-                    "Model must be exported before the 'paths' attribute is" \
+                    "Model must be exported before the 'paths' attribute is"
                     "available for a DistribcellFilter.")
 
             # Determine paths for cell instances

openmc/mesh.py

@@ -693,7 +693,7 @@ def num_mesh_cells(self):
     def write_data_to_vtk(self,
                           filename: PathLike,
                           datasets: dict | None = None,
-                          volume_normalization: bool = False,
+                          volume_normalization: bool | None = None,
                           curvilinear: bool = False):
         """Creates a VTK object of the mesh
 
@@ -709,9 +709,10 @@ def write_data_to_vtk(self,
             with structured indexing in "C" ordering. See the "expand_dims" flag
             of :meth:`~openmc.Tally.get_reshaped_data` on reshaping tally data when using
             :class:`~openmc.MeshFilter`'s.
-        volume_normalization : bool, optional
+        volume_normalization : bool or None, optional
             Whether or not to normalize the data by the volume of the mesh
-            elements.
+            elements. When None (default), the format-appropriate default is
+            used: True for legacy ASCII .vtk files, False for .vtkhdf files.
         curvilinear : bool
             Whether or not to write curvilinear elements. Only applies to
             ``SphericalMesh`` and ``CylindricalMesh``.
@@ -748,10 +749,14 @@ def write_data_to_vtk(self,
             if write_impl is None:
                 raise NotImplementedError(
                     f"VTKHDF output not implemented for {type(self).__name__}")
-            # write_impl is a bound method – do NOT pass self again
-            write_impl(filename, datasets, volume_normalization)
+            # vtkhdf default is False; explicit value is respected
+            norm = volume_normalization if volume_normalization is not None else False
+            write_impl(filename, datasets, norm)
             return None
 
+        # legacy ASCII .vtk default is True
+        norm = volume_normalization if volume_normalization is not None else True
+
         # vtk is an optional dependency only needed for the legacy ASCII path
         import vtk
         from vtk.util import numpy_support as nps
@@ -769,20 +774,26 @@ def write_data_to_vtk(self,
             # maintain a list of the datasets as added to the VTK arrays to
             # ensure they persist in memory until the file is written
             datasets_out = []
+            # Regular/Rectilinear meshes store data in C (ijk) order which
+            # matches VTK's expected ordering directly — no transpose needed.
+            # Curvilinear meshes (Cylindrical, Spherical) require a transpose
+            # to convert from C ordering to the Fortran (kji) ordering that VTK
+            # expects.
+            # TODO: update to "C" ordering throughout
+            needs_transpose = not isinstance(
+                self, (RegularMesh, RectilinearMesh))
             for label, dataset in datasets.items():
                 dataset = self._reshape_vtk_dataset(dataset)
                 self._check_vtk_dataset(label, dataset)
-                # If the array data is 3D, assume is in C ordering and transpose
-                # before flattening to match the ordering expected by the VTK
-                # array based on the way mesh indices are ordered in the Python
-                # API
-                # TODO: update to "C" ordering throughout
                 if dataset.ndim == 3:
-                    dataset = dataset.ravel()
+                    dataset = dataset.T.ravel() if needs_transpose else dataset.ravel()
                 datasets_out.append(dataset)
 
-                if volume_normalization:
-                    dataset /= self.volumes.ravel()
+                if norm:
+                    if needs_transpose:
+                        dataset /= self.volumes.T.ravel()
+                    else:
+                        dataset /= self.volumes.ravel()
 
                 dataset_array = vtk.vtkDoubleArray()
                 dataset_array.SetName(label)

tests/unit_tests/test_mesh.py

@@ -1217,7 +1217,10 @@ def test_write_ascii_vtk_unchanged(run_in_tmpdir):
 
     # This should work without requiring vtk module changes
     vtkIOLegacy = pytest.importorskip("vtkmodules.vtkIOLegacy")
-    mesh.write_data_to_vtk(datasets={"data": ref_data}, filename=filename)
+    mesh.write_data_to_vtk(datasets={"data": ref_data},
+                           filename=filename,
+                           volume_normalization=False
+                           )
 
     assert Path(filename).exists()