use python to randomly inset each face, bmesh?

Question

I would like to create some interesting shapes with a script. I'm still pretty new to python and I'm having trouble understanding how to get BMesh to behave the way I want. Here is what I'm trying to accomplish.

1. Randomly inset faces a random length, with some not being inset at all.

2. Advanced function: randomly inset again excluding the 4 faces around original insets (if that makes sense)

   import bpy
   import bmesh
   from random import randint, random
   
   obj = bpy.context.active_object
   
   bm = bmesh.new()
   bm.from_mesh(obj.data,face_normals=True)
   
   for faces in bm.faces:
       if randint(0,1) > 0:
           bmesh.ops.inset_region(bm, faces=bm.faces, thickness=0.4, depth=randint(0,1))
   
   bm.to_mesh(obj.data)
   bm.free()
   obj.data.update()
   

Here is an idea of what I'm going for generated from a cube.

Answer 1

You can't loop through bm.faces, because you are creating more faces in the loop, which are also iterated over. Instead make a copy of the faces

faces_copy = [f for f in bm.faces]

Now, your code would give us the following result.

Notable problems - Insets, even at 0 depth. - Your example image shows and inset with 0 depth and then a random extrusion.

Let's implement that. Luckily, after a inset_region operation, the face index stays the same so we can simply extrude it by insetting another time and moving the face's vertices along the face normal.

bmesh.ops.inset_region(bm, faces = [face], thickness=0.4, depth=0)
bmesh.ops.inset_region(bm, faces = [face], thickness=0, depth=0)
bmesh.ops.translate(bm, verts = face.verts, vec = face.normal)

Now lets add the randomness:

import random
#[...]

bmesh.ops.inset_region(bm, faces = [face], thickness=random.uniform(0.1, 0.9), depth=0)
bmesh.ops.inset_region(bm, faces = [face], thickness=0, depth=0)
bmesh.ops.translate(bm, verts = face.verts, vec = face.normal * random.uniform(0.1, 4))

Iterations

We need to catch the newly "extruded" faces. Luckily inset_region returns geometry. We can create a new face list like this:

geom = bmesh.ops.inset_region(bm, faces = [face], thickness=0, depth=0)
new_faces = geom['faces'] # list of bmesh faces

Create an empty list for the new faces. After the insetting and extrusion, we'll add the active face and the extruded side faces.

new_faces.extend(geom['faces'])
new_faces.append(face)

Complete code (with two iterations):

import bpy
import bmesh
import random
from mathutils import Vector

obj = bpy.context.active_object

bm = bmesh.new()
bm.from_mesh(obj.data,face_normals=True)

# faces, which could be extruded
faces_copy = [f for f in bm.faces]
new_faces = []
# number of iterations goes here
for i in range(0, 2):
    for face in faces_copy:
        do_inset = random.randint(0,1)
        if do_inset:
            bmesh.ops.inset_region(bm, faces = [face], thickness=random.uniform(0.1, 0.9), depth=0)
            geom = bmesh.ops.inset_region(bm, faces = [face], thickness=0, depth=0)
            bmesh.ops.translate(bm, verts = face.verts, vec = face.normal * random.uniform(0.1, 4))
            new_faces.extend(geom['faces'])
            new_faces.append(face)
    faces_copy = new_faces
    new_faces = []

bm.to_mesh(obj.data)
bm.free()
obj.data.update()

The concept is pretty cool, but it already show, that we need to implement a method to take the faces size into account before using bmesh.ops.translate.