disjoint meshes set theory

find_islands.py

verts = [[1.101621389389038, 0.541892945766449, 0.0], [0.8510395884513855, -0.006982157006859779, 0.0], [0.7924670577049255, -0.006982157006859779, 0.0], [0.5302482843399048, 0.541892945766449, 0.0], [0.677261471748352, 0.541892945766449, 0.0], [0.8203957080841064, 0.23273855447769165, 0.0], [0.9561598300933838, 0.541892945766449, 0.0], [0.37742435932159424, 0.541892945766449, 0.0], [0.6179208755493164, 0.0, 0.0], [0.4728471636772156, 0.0, 0.0], [0.42823895812034607, 0.10705973953008652, 0.0], [0.18580295145511627, 0.10705973953008652, 0.0], [0.14546160399913788, 0.0, 0.0], [0.0023273855913430452, 0.0, 0.0], [0.22071373462677002, 0.541892945766449, 0.0], [0.38828548789024353, 0.20170675218105316, 0.0], [0.30100852251052856, 0.4123351573944092, 0.0], [0.2214895337820053, 0.20170675218105316, 0.0]] 

faces = [[2, 4, 3], [2, 5, 4], [5, 0, 6], [5, 1, 0], [2, 1, 5], [13, 7, 14], [13, 16, 7], [16, 8, 7], [13, 17, 16], [15, 8, 16], [13, 11, 17], [11, 15, 17], [11, 10, 15], [10, 8, 15], [13, 12, 11], [9, 8, 10]]


import itertools
from collections import defaultdict

def process_to_boundaries(vex, pox):
    edges = defaultdict(int)
    
    for poly in pox:
        for idx in range(len(poly)-1):
            edge = tuple(sorted([poly[idx], poly[idx+1]]))
            edges[edge] += 1
        edge = tuple(sorted([poly[-1], poly[0]]))
        edges[edge] += 1
    
    return [k for k, v in edges.items() if v == 1]

def process_to_islands(vex, pox):
    islands = defaultdict(set)
    for poly in pox:
        first_idx = list(sorted(poly))[0]
        islands[f"{first_idx}"].update(poly)
    

    interim_islands = list(islands.values())

    def merge_islands(islands):

        found_island_part = False
        
        num_islands = len(islands)
        new_island_dict = defaultdict(set)
        combo_matrix = []

        permut = itertools.permutations(list(range(num_islands)), 2)
        combos = set([tuple(sorted(e)) for e in permut])
        for c in combos:
            intersect = islands[c[0]] & islands[c[1]]
            if intersect:
                found_island_part = True
                combo_matrix.append(c)
        
        if not found_island_part:
            return islands
        else:
            
            lusax = [set(i) for i in combo_matrix]
            for c in combo_matrix:
                for idx, subset in enumerate(lusax):
                    if set(c) & subset:
                        # if subset already taken in the past skip the !=
                        lusax[idx] |= set(c)
                        continue
        
            new_proto_islands = set(frozenset(i) for i in lusax)
            new_islands = list()
            for merge_indices in new_proto_islands:
                disjoint = [islands[i] for i in merge_indices]
                disjoint = set(itertools.chain(*disjoint))
                new_islands.append(disjoint)

            return merge_islands(new_islands)

    return merge_islands(interim_islands)



boundaries = process_to_boundaries(verts, faces)
print(boundaries)
# 
islands = process_to_islands(verts, faces)
print(islands)