Add recombine option to generate quadrilateral meshes (#290)

src/skgmsh/__init__.py

@@ -177,7 +177,8 @@ def delaunay_3d(
 def frontal_delaunay_2d(
     edge_source: pv.PolyData,
     target_sizes: float | Sequence[float] | None = None,
-) -> pv.PolyData | None:
+    recombine: bool = False,  # noqa: FBT001, FBT002
+) -> pv.UnstructuredGrid | None:
     """
     Frontal-Delaunay 2D mesh algorithm.
 
@@ -195,9 +196,12 @@ def frontal_delaunay_2d(
         Target mesh size close to the points.
         Default max size of edge_source in each direction.
 
+    recombine : bool
+        Recombine the generated mesh into quadrangles.
+
     Returns
     -------
-    pyvista.PolyData
+    pyvista.UnstructuredGrid
         Mesh from the 2D delaunay generation.
 
     Notes
@@ -240,12 +244,17 @@ def frontal_delaunay_2d(
 
     gmsh.model.mesh.embed(0, embedded_points, 2, 1)
 
+    if recombine:
+        gmsh.model.mesh.setRecombine(2, 1)
+
     gmsh.model.mesh.generate(2)
-    mesh = extract_to_meshio()
+    mesh = pv.from_meshio(extract_to_meshio())
     gmsh.clear()
     gmsh.finalize()
 
-    for cell in mesh.cells:
-        if cell.type == "triangle":
-            return pv.PolyData.from_regular_faces(mesh.points, cell.data)
-    return None
+    ind = []
+    for index, cell in enumerate(mesh.cell):
+        if cell.type in [pv.CellType.VERTEX, pv.CellType.LINE]:
+            ind.append(index)
+
+    return mesh.remove_cells(ind)

tests/test_skgmsh.py

@@ -28,6 +28,17 @@ def test_frontal_delaunay_2d_default() -> None:
     # https://github.com/pyvista/scikit-gmsh/pull/125
 
 
+def test_frontal_delaunay_2d_recombine() -> None:
+    """Frontal-Delaunay 2D mesh algorithm test code."""
+    edge_source = pv.Polygon(n_sides=4, radius=8)
+    mesh = sg.frontal_delaunay_2d(edge_source, recombine=True)
+    assert mesh.number_of_points == edge_source.number_of_points
+    assert mesh.number_of_cells == 1
+    assert np.allclose(mesh.volume, edge_source.volume)
+    for cell in mesh.cell:
+        assert cell.type == pv.CellType.QUAD
+
+
 @pytest.mark.parametrize("edge_source", EDGE_SOURCES)
 @pytest.mark.parametrize("target_sizes", [2.0, [1.0, 2.0, 3.0, 4.0]])
 def test_frontal_delaunay_2d(