Add CSG2d tutorial

py_tutorials/csg2d.py

@@ -0,0 +1,50 @@
+from ngsolve import *
+
+from random import random, seed
+ngsglobals.msg_level = 0
+
+import netgen
+from pyngcore import *
+from netgen.geom2d import *
+
+seed(4)
+
+def GenerateMesh():
+
+    g = CSG2d()
+    g1 = CSG2d()
+    outer = Rectangle(0, 1, 0, 1,"outer","outer")
+    inner = Solid2d()
+
+    for i in range(30):
+        cx = random()
+        cy = random()
+        r  = 0.03+0.05*random()
+        print("Add Circle", i, cx, cy, r, flush = True)
+        circle = Circle(cx, cy, r, "circle"+str(i), "circle"+str(i))
+        g1.Add(circle)
+        inner += circle
+        outer -= circle
+
+
+    g.Add(inner)
+    g.Add(outer)
+    geo = g.GenerateSplineGeometry()
+    Draw(geo)
+
+    # draw this geometry for checking ff the final mesh/geometry is correct
+    # g1.Add(outer)
+    # geo1 = g1.GenerateSplineGeometry()
+    # Draw(geo1)
+
+    print('generate mesh')
+    m = geo.GenerateMesh(maxh=0.1)
+    mesh = Mesh(m)
+    mesh.Curve(3)
+    Draw(mesh)
+
+    return mesh
+
+from ngsolve import Draw
+with PajeTrace():
+    mesh = GenerateMesh()