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 +1112,14 @@ 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 using by_element so ordering is deterministic (volume
+        # ascending, material ID as tiebreaker) regardless of the ray-traversal
+        # order returned by the C library.
+        bins = []
+        for i in range(volumes.num_elements):
+            for mat_id, _ in volumes.by_element(i):
+                if mat_id is not None:
+                    bins.append((i, mat_id))
         return cls(mesh, bins)
 
     def __hash__(self):
@@ -1861,7 +1862,7 @@ 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 +2172,7 @@ 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

@@ -160,6 +160,11 @@ def by_element(
             else:
                 results.append((mat_id, vol))
 
+        # Sort by volume (ascending) so output is deterministic regardless of
+        # the ray-traversal order returned by the C library. Ties are broken by
+        # material ID (ascending). None (void) sorts after all real material IDs.
+        results.sort(key=lambda t: (
+            t[0] is None, t[1], t[0] if t[0] is not None else float('inf')))
         return results
 
     def save(self, filename: PathLike):

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()