Add option constrain_edge_size for Delaunay2D

[keurfonluu]

Overview

This PR adds an option that calculates cell size based on edge lengths.

Default behavior:

import pyvista as pv
import skgmsh as sg

edge_source = pv.Polygon(n_sides=16, radius=16)
mesh = sg.Delaunay2D(shell=edge_source.points).mesh

p = pv.Plotter()
p.add_mesh(mesh, show_edges=True)
p.add_mesh(pv.PolyData(edge_source.points), render_points_as_spheres=True, color="red", point_size=10)
p.view_xy()
p.show()

With option constrain_edge_size=True:

mesh = sg.Delaunay2D(shell=edge_source.points, constrain_edge_size=True).mesh

Works with holes too!

hole1 = pv.Polygon(n_sides=6, radius=4).translate([-4.0, -4.0, 0.0])
hole2 = pv.Polygon(n_sides=8, radius=2).translate([4.0, 4.0, 0.0])
mesh = sg.Delaunay2D(shell=edge_source.points, holes=[hole1.points, hole2.points], constrain_edge_size=True).mesh

Which looks much better than if we simply forced Frontal Delaunay in the source code:

gmsh.option.set_number("Mesh.Algorithm", FRONTAL_DELAUNAY_2D)

[tkoyama010]

I’m thinking of adding the wonderful examples you provided to the examples directory.