Add Quad geometry example to add customize Delaunay2D class (#409)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

examples/quad.py

@@ -0,0 +1,51 @@
+r"""
+Quad geometry example
+---------------------
+
+Quad geometry example.
+
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+import subprocess
+from typing import Optional
+
+import pyvista as pv
+import shapely
+
+
+class Delaunay2D:
+    """Delaunay2D class."""
+
+    def __init__(self, shell: shapely.Polygon, holes: Optional[list[shapely.Polygon]] = None) -> None:
+        """Create a Delaunay2D object."""
+        self.shell = shapely.Polygon(shell)
+        self.holes = [shapely.Polygon(hole) for hole in holes] if holes else []
+        self._generate_mesh()
+
+    def _generate_mesh(self) -> None:
+        cell_size = 0.05
+        with Path("quad.geo").open("w") as f:
+            for linearring in [self.shell.exterior, *list(self.shell.interiors), *self.holes]:
+                coords = linearring.coords[:-1].copy()
+                for i, coord in enumerate(coords):
+                    x = coord[0]
+                    y = coord[1]
+                    z = coord[2]
+                    f.write("Point(" + str(i + 1) + ") = {" + str(x) + "," + str(y) + "," + str(z) + "," + str(cell_size) + "};\n")
+                for i, _ in enumerate(coords[:-1]):
+                    f.write("Line(" + str(i + 1) + ") = {" + str(i + 1) + ", " + str(i + 2) + "};\n")
+                f.write("Line(" + str(len(coords)) + ") = {" + str(len(coords)) + ", 1};\n")
+                f.write("Line Loop(1) = {")
+                for i in range(len(coords) - 1):
+                    f.write(str(i + 1) + ", ")
+                f.write(str(len(coords)) + "};\n")
+                f.write("Plane Surface(1) = {1};\n")
+        subprocess.run(["gmsh", "quad.geo", "-2", "-o", "quad.vtk"], check=False)  # noqa: S603, S607
+        self.mesh = pv.read("quad.vtk")
+
+
+alg = Delaunay2D([(0, 0, 0), (1, 0, 0), (1, 1, 0), (0, 1, 0)])
+alg.mesh.plot(show_edges=True, color="w", cpos="xy")