Select connected faces to a FACET about trimesh HOT 4 CLOSED

In [1]: import trimesh

In [2]: m = trimesh.load('models/featuretype.STL')

In [3]: m
Out[3]: <trimesh.Trimesh(vertices.shape=(1722, 3), faces.shape=(3476, 3), name=`featuretype.STL`)>

In [4]: facet = m.facets[0]

In [5]: facet
Out[5]: 
array([  0, 286, ...  134, 133, 132, 130])

In [7]: import numpy as np

In [8]: facet_mask = np.zeros(len(m.faces), dtype=bool)

In [10]: facet_mask[facet] = True

# get pairs of faces where only *one* of them is included in the facet
In [11]: border = facet_mask[m.face_adjacency].sum(axis=1) == 1

In [12]: border.shape
Out[12]: (5214,)

In [14]: border
Out[14]: array([ True, False, False, ..., False, False, False])

In [15]: border.sum()
Out[15]: 374

# (m, 2) indexes of m.faces
In [16]: adjacent = m.face_adjacency[border]

In [21]: other_faces = adjacent.ravel()[~facet_mask[adjacent.ravel()]]

# make the facet blue
In [22]: m.visual.face_colors[facet] = [0,0,255,255]

# border faces red
In [23]: m.visual.face_colors[other_faces] = [255,0,0,255]

In [24]: m.show(smooth=False)

cc_mask = np.zeros(len(m.faces), dtype=np.bool)
cc_mask[np.concatenate(cc_mask)] = True

# make the facet blue
m.visual.face_colors[facet] = [0,0,255,255]

# attached facets red
m.visual.face_colors[cc_mask] = [255,0,0,255]   
m.show(smooth=False)

# create a new mesh from selected cc
cc_m = m.copy()
cc_m.update_faces(cc_mask)