OBJ Import and vertex groups

Coding Python Support
1

edit: the fix is further down
(I have an ugly hack to do this manually with IDLE.
the interesting part would be the next post)

problem: OBJ import loses set membership list. (for vertex groups)

the task:
assign the set membership of verts (maya) to blender vertex groups.
-take a piece of MEL code that selects a set of vertices and convert it to a piece of blender python that can be run from the text editor in Blender, so the resultant selected verts can be assigned to a vertex group - optionally, automate the assignment to vertex group(s).
OBJ vertex numbering begins at 1.
maya and blender both begin at 0.

Here’s what you get in maya when you select a set, then when you drag select the membership :
select -r -ne L_elbowSet ; // this is the set
select -r rabbit.vtx[9] rabbit.vtx[10] rabbit.vtx[11] rabbit.vtx[12] rabbit.vtx[21] rabbit.vtx[22] rabbit.vtx[23] rabbit.vtx[24] rabbit.vtx[33] rabbit.vtx[34] rabbit.vtx[36] rabbit.vtx[67] rabbit.vtx[68] rabbit.vtx[69] rabbit.vtx[80] rabbit.vtx[81] rabbit.vtx[82] rabbit.vtx[86] rabbit.vtx[87] rabbit.vtx[90] rabbit.vtx[91] rabbit.vtx[92] ;

  • a utility to take the above list of verts and put it in a form blender will be able to use to select the verts. Preferably reads a file and saves to a new file, and runs from IDLE.
  • a script to run from inside blender to select a list of verts (so I can manually create a vertex group and assign the selection to it)
    optional script to create the vertex group based on the set name; add the selected verts to the group.

in blender, I need:
? will the verts be same numbered ? // we can hope.
to work the mesh … (find how it is refered in blender)
probably have to be in edit mode
create vertex groups for the mesh
name ‘L_elbowSet’ // could be set1, etc… for all I care. They will get renamed again before I am done.
add each vert to the selection // the important part
assign the selection to the vertex group

what would be the script to select a vert based on it’s index?
add (or append) a vert to a selection?

pseudo code:

need clever name for script v1.0

extract list of values from MEL data, save to file

import Blender
replace = Blender.Mesh.AssignModes.REPLACE
mesh = rabbit.getData(mesh=True)
mesh.addVertGroup(‘renameMe’)

read the data and put it into a list

vertList = [] # list of integers

mesh.assignVertsToGroup(‘renameMe’, vertList, 1.0, replace)

2

Of course the better option would be to redo the OBJ importer, of which there are legends but scant signs of a fixed version.

3

looking at import_obj.py
…create_mesh…
line 545


# Create the vertex groups. No need to have the flag passed here since we test for the 
# content of the vertex_groups. If the user selects to NOT have vertex groups saved then
# the following test will never run
for group_name, group_indicies in vertex_groups.iteritems():
 me.addVertGroup(group_name)
 me.assignVertsToGroup(group_name, group_indicies,1.00, Mesh.AssignModes.REPLACE)

Unfortunately, the only group that will get verts assigned is the last one in the OBJ file-
the mesh name in my case.
…load_obj…
line 727


if line.startswith('v '):
 line_split= line.split()
 # rotate X90: (x,-z,y)
 verts_loc.append( (float_func(line_split[1]), -float_func(line_split[3]), float_func(line_split[2])) )

ok it has a vert. it will either do this again for the next line, close the file, or some of the following:
line 741


elif line.startswith('f') or context_multi_line == 'f':

…
I am assuming context_multi_line is supposed to track blocks of lines beginning with ‘f’
line 761


if strip_slash(line_split):
 context_multi_line = 'f'
else:
 context_multi_line = ''

my assumption is probably incorrect.
line 770


# Add the vertex to the current group
# *warning*, this wont work for files that have groups defined around verts
if POLYGROUPS and context_vgroup:
 vertex_groups[context_vgroup].append(vert_loc_index)

This code piece is outside of the part that looks for groups on the OBJ file.
line 848


elif line.startswith('g'):
 if SPLIT_GROUPS:
  context_object= line_value(line.split())
  # print 'context_object', context_object
  # unique_obects[context_object]= None
 elif POLYGROUPS:
  context_vgroup = line_value(line.split())
  if context_vgroup and context_vgroup != '(null)':
   vertex_groups.setdefault(context_vgroup, [])
  else:
   context_vgroup = None # dont assign a vgroup

This seems to save the name of a group.
Perhaps the setdefault makes the group the default vert group, then the next group to appear becomes the default -
which could explain why only the last group in the OBJ file is getting all the vertices.

4

mesh (with sets) exported from maya as OBJ
set names are not too complicated - spaces and other crap may mess this up.
for my OBJ files, or if your OBJ files is in format:
g groupname(a)
v vertdata
v vert data
g groupname(b)
v
v
g another group name ( could be repeats)
etc…
the following should import the OBJ with the OBJ’s groups converted into vertex groups
note:
Keep vert order
Poly groups
image search (optional)
on, all others OFF

copy import_obj.py
change filename to import_DOG_obj.py

modify lines where create_mesh is defined and called to include filepath
335 and 956(if new code allready pasted 988)
def create_mesh(filepath, # etc

line 4: to distinguish from import_obj
Name: ‘DOG Wavefront (.obj)…’

code to look for at lines 545-550


 # Create the vertex groups. No need to have the flag passed here since we test for the 
 # content of the vertex_groups. If the user selects to NOT have vertex groups saved then
 # the following test will never run
 for group_name, group_indicies in vertex_groups.iteritems():
  me.addVertGroup(group_name)
  me.assignVertsToGroup(group_name, group_indicies,1.00, Mesh.AssignModes.REPLACE)

add at line 551, after the existing code for vertex groups


 # DOG  vertex groups
 if POLYGROUPS :
  # go through the file from the start
  file= open(filepath, 'rU') # from line 723
  groupname = ''
  # start index counter at 0
  vindex = 0
  for line in file: #.xreadlines(): # get the next line
    line = line.lstrip() # rare cases there is white space at the start of the line
    if line.startswith('g'): # is the line a group?
     # find out the group name, make it the current group
 
     groupline = line.split()
     groupname = groupline[1]
    elif line.startswith('v '): # is the line a vertice?
     # check for a current group
     if groupname : # probably need error check for screwy names, names with spaces etc.
      # add the index to the current group
      vList =[] # avoid a type error
      vList.append(vindex)
      # print '
', groupname, ' ', vList, '
'
      me.assignVertsToGroup(groupname, vList, 1.00, Mesh.AssignModes.ADD)
     # increment the index
     vindex += 1
 
    # would be nice to check for obvious end of possible vertex groups
    # if the line is anything else
     # do nothing
 
  file.close()

save in scripts directory