Wavefront OBJ normal export problem

Hello. I created a simple terrain for a game that I am working on, and when I exported the model as a Wavefront OBJ file, the normals were completely wrong. All of the faces should be facing up (in the +z direction), but in the exported file, the normals are facing in the +y direction. Oddly, in another model that I created, a space ship, the normals appear to have been exported correctly. This is using the built-in exporter that came with Blender 2.37a.

How can I get correct normals? If it would be helpful, I can supply the .blend file and the .obj file.

I noticed that there was a newer version of Blender, so I upgraded to 2.40, and the export behaves in the same way. In the console, the only information given is as follows:

Using Python version 2.4
obj export time: 0.05

I have uploaded the offending files here:

http://people.cs.tamu.edu/jmm9179/files/area.blend
http://people.cs.tamu.edu/jmm9179/files/area.obj

Try this one…

#!BPY

"""
Name: 'Wavefront (.obj)...'
Blender: 232
Group: 'Export'
Tooltip: 'Save a Wavefront OBJ File'
"""

__author__ = "Campbell Barton, Jiri Hnidek"
__url__ = ["blender", "elysiun"]
__version__ = "1.0"

__bpydoc__ = """\
This script is an exporter to OBJ file format.

Usage:

Run this script from "File->Export" menu to export all meshes.
"""


# --------------------------------------------------------------------------
# OBJ Export v0.9b by Campbell Barton (AKA Ideasman)
# --------------------------------------------------------------------------
# ***** BEGIN GPL LICENSE BLOCK *****
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 2
# of the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software Foundation,
# Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
#
# ***** END GPL LICENCE BLOCK *****
# --------------------------------------------------------------------------

#==================================================#
# New name based on old with a different extension #
#==================================================#
def newFName(ext):
	return Get('filename')[: -len(Get('filename').split('.', -1)[-1]) ] + ext


def fixName(name):
	if name == None:
		return 'None'
	else:
		return name.replace(' ', '_')

def getMeshFromObject(object, name=None, mesh=None):
	if mesh:
		mesh.verts = None # Clear the meshg
	else:
		if not name:
			mesh = Mesh.New()
		else:
			mesh = Mesh.New(name)
	
	
	type = object.getType()
	dataname = object.getData(1)
	
	try:
		mesh.getFromObject(object.name) 
	except:
		return None
	
	if type == 'Mesh':
		tempMe = Mesh.Get( dataname )
		mesh.materials = tempMe.materials
		mesh.degr = tempMe.degr
		mesh.mode = tempMe.mode
	else:
		try:
			# Will only work for curves!!
			# Text- no material access in python interface.
			# Surf- no python interface
			# MBall- no material access in python interface.
			
			data = object.getData()
			materials = data.getMaterials()
			mesh.materials = materials
			print 'assigning materials for non mesh'
		except:
			print 'Cant assign materials to', type
	
	return mesh



from Blender import *

global MTL_DICT

# A Dict of Materials
# (material.name, image.name):matname_imagename # matname_imagename has gaps removed.
MTL_DICT = {} 

def save_mtl(filename):
	global MTL_DICT
	
	world = World.GetCurrent()
	if world:
		worldAmb = world.getAmb()
	else:
		worldAmb = (0,0,0) # Default value
	
	file = open(filename, "w")
	file.write('# Blender MTL File: %s
' % Get('filename').split('\\')[-1].split('/')[-1])
	file.write('# Material Count: %i
' % len(MTL_DICT))
	# Write material/image combinations we have used.
	for key, mtl_mat_name in MTL_DICT.iteritems():
		
		# Get the Blender data for the material and the image.
		# Having an image named None will make a bug, dont do it :)
		
		file.write('newmtl %s
' % mtl_mat_name) # Define a new material: matname_imgname
		
		if key[0] == None:
			#write a dummy material here?
			file.write('Ns 0
')
			file.write('Ka %s %s %s
' %  tuple([round(c, 6) for c in worldAmb])  ) # Ambient, uses mirror colour,
			file.write('Kd 0.8 0.8 0.8
')
			file.write('Ks 0.8 0.8 0.8
')
			file.write('d 1
') # No alpha
			file.write('illum 2
') # light normaly	
			
		else:
			mat = Material.Get(key[0])
			file.write('Ns %s
' % round((mat.getHardness()-1) * 1.9607843137254901 ) ) # Hardness, convert blenders 1-511 to MTL's 
			file.write('Ka %s %s %s
' %  tuple([round(c*mat.getAmb(), 6) for c in worldAmb])  ) # Ambient, uses mirror colour,
			file.write('Kd %s %s %s
' % tuple([round(c*mat.getRef(), 6) for c in mat.getRGBCol()]) ) # Diffuse
			file.write('Ks %s %s %s
' % tuple([round(c*mat.getSpec(), 6) for c in mat.getSpecCol()]) ) # Specular
			file.write('Ni %s
' % round(mat.getIOR(), 6)) # Refraction index
			file.write('d %s
' % round(mat.getAlpha(), 6)) # Alpha (obj uses 'd' for dissolve)
			
			# 0 to disable lighting, 1 for ambient & diffuse only (specular color set to black), 2 for full lighting.
			if mat.getMode() & Material.Modes['SHADELESS']:
				file.write('illum 0
') # ignore lighting
			elif mat.getSpec() == 0:
				file.write('illum 1
') # no specular.
			else:
				file.write('illum 2
') # light normaly	
		
		
		# Write images!
		if key[1] != None:  # We have an image on the face!
			img = Image.Get(key[1])
			file.write('map_Kd %s
' % img.filename.split('\\')[-1].split('/')[-1]) # Diffuse mapping image			
		
		elif key[0] != None: # No face image. if we havea material search for MTex image.
			for mtex in mat.getTextures():
				if mtex and mtex.tex.type == Texture.Types.IMAGE:
					try:
						filename = mtex.tex.image.filename.split('\\')[-1].split('/')[-1]
						file.write('map_Kd %s
' % filename) # Diffuse mapping image
						break
					except:
						# Texture has no image though its an image type, best ignore.
						pass
		
		file.write('

')
	
	file.close()



def save_obj(filename):
	global MTL_DICT
	temp_mesh_name = '~tmp-mesh'
	time1 = sys.time()
	scn = Scene.GetCurrent()

	file = open(filename, "w")
	
	# Write Header
	file.write('# Blender OBJ File: %s
' % (Get('filename').split('/')[-1].split('\\')[-1] ))
	file.write('# www.blender.org
')

	# Tell the obj file what material file to use.
	mtlfilename = '%s.mtl' % '.'.join(filename.split('.')[:-1])
	file.write('mtllib %s
' % ( mtlfilename.split('\\')[-1].split('/')[-1] ))
	
	# Get the container mesh.
	containerMesh = meshName = tempMesh = None
	for meshName in NMesh.GetNames():
		if meshName.startswith(temp_mesh_name):
			tempMesh = Mesh.Get(meshName)
			if not tempMesh.users:
				containerMesh = tempMesh
	if not containerMesh:
		containerMesh = Mesh.New(temp_mesh_name)
	del meshName
	del tempMesh
	
	
	
	# Initialize totals, these are updated each object
	totverts = totuvco = totno = 1
	
	globalUVCoords = {}
	globalNormals = {}
	
	# Get all meshs
	for ob in scn.getChildren():
		#for ob in Object.GetSelected():
		
		# Will work for non meshes now! :)
		#m = NMesh.GetRawFromObject(ob.name)
		m = getMeshFromObject(ob, temp_mesh_name, containerMesh, )
		if not m:
			continue
		
		
		#faces = [ f for f in m.faces if len(f) > 2 ]
		faces = [ f for f in m.faces ]
		
		if not faces: # Make sure there is somthing to write
			continue # dont bother with this mesh.
		
		m.transform(ob.matrix)
		
		# # Crash Blender
		#materials = m.getMaterials(1) # 1 == will return None in the list.
		materials = m.materials
		
		
		if materials:
			materialNames = map(lambda mat: mat.name, materials) # Bug Blender, dosent account for null materials, still broken.	
		else:
			materialNames = []
		
		# Possible there null materials, will mess up indicies
		# but at least it will export, wait until Blender gets fixed.
		materialNames.extend((16-len(materialNames)) * [None])
		
		
		# Sort by Material, then images
		# so we dont over context switch in the obj file.
		if m.faceUV:
			faces.sort(lambda a,b: cmp((a.mat, a.image, a.smooth), (b.mat, b.image, b.smooth)))
		else:
			faces.sort(lambda a,b: cmp((a.mat, a.smooth), (b.mat, b.smooth)))
		
		
		# Set the default mat to no material and no image.
		contextMat = (0, 0) # Can never be this, so we will label a new material teh first chance we get.
		contextSmooth = None # Will either be true or false,  set bad to force initialization switch.
		
		file.write('o %s_%s
' % (fixName(ob.name), fixName(m.name))) # Write Object name
		
		# Vert
		for v in m.verts:
			file.write('v %.6f %.6f %.6f
' % tuple(v.co))
		
		# UV
		if m.faceUV:
			for f in faces:
				for uvKey in f.uv:
					uvKey = tuple(uvKey)
					if not globalUVCoords.has_key(uvKey):
						globalUVCoords[uvKey] = totuvco
						totuvco +=1
						file.write('vt %.6f %.6f 0.0
' % uvKey)
		
		# NORMAL, Smooth/Non smoothed.
		
		for f in faces:
			if f.smooth:
				for v in f.v:
					noKey = tuple(v.no)
					if not globalNormals.has_key( noKey ):
						globalNormals[noKey] = totno
						totno +=1
						file.write('vn %.6f %.6f %.6f
' % noKey)
			else:
				# Hard, 1 normal from the face.
				noKey = tuple(f.no)
				if not globalNormals.has_key( noKey ):
					globalNormals[noKey] = totno
					totno +=1
					file.write('vn %.6f %.6f %.6f
' % noKey)
		
		
		uvIdx = 0
		for f in faces:
			
			# MAKE KEY
			if m.faceUV and f.image: # Object is always true.
				key = materialNames[f.mat],  f.image.name
			else:
				key = materialNames[f.mat],  None # No image, use None instead.
			
			# CHECK FOR CONTEXT SWITCH
			if key == contextMat:
				pass # Context alredy switched, dont do anythoing
			elif key[0] == None and key[1] == None:
				# Write a null material, since we know the context has changed.
				file.write('usemtl (null)
') # mat, image
				
			else:
				try: # Faster to try then 2x dict lookups.
					
					# We have the material, just need to write the context switch,
					file.write('usemtl %s
' % MTL_DICT[key]) # mat, image
					
				except KeyError:
					# First add to global dict so we can export to mtl
					# Then write mtl
					
					# Make a new names from the mat and image name,
					# converting any spaces to underscores with fixName.
					
					# If none image dont bother adding it to the name
					if key[1] == None:
						tmp_matname = MTL_DICT[key] ='%s' % fixName(key[0])
						file.write('usemtl %s
' % tmp_matname) # mat, image
						
					else:
						tmp_matname = MTL_DICT[key] = '%s_%s' % (fixName(key[0]), fixName(key[1]))
						file.write('usemtl %s
' % tmp_matname) # mat, image
				
			contextMat = key
			
			if f.smooth != contextSmooth:
				if f.smooth:
					file.write('s 1
')
				else:
					file.write('s off
')
				contextSmooth = f.smooth
			
			file.write('f')
			if m.faceUV:
				if f.smooth: # Smoothed, use vertex normals
					for vi, v in enumerate(f.v):
						file.write( ' %d/%d/%d' % (\
						  v.index+totverts,\
						  globalUVCoords[ tuple(f.uv[vi]) ],\
						  globalNormals[ tuple(v.no) ])) # vert, uv, normal
				else: # No smoothing, face normals
					no = globalNormals[ tuple(f.no) ]
					for vi, v in enumerate(f.v):
						file.write( ' %d/%d/%d' % (\
						  v.index+totverts,\
						  globalUVCoords[ tuple(f.uv[vi]) ],\
						  no)) # vert, uv, normal
			
			else: # No UV's
				if f.smooth: # Smoothed, use vertex normals
					for v in f.v:
						file.write( ' %d//%d' % (\
						  v.index+totverts,\
						  globalNormals[ tuple(v.no) ]))
				else: # No smoothing, face normals
					no = globalNormals[ tuple(f.no) ]
					for v in f.v:
						file.write( ' %d//%d' % (\
						  v.index+totverts,\
						  no))
					
			file.write('
')
		
		# Make the indicies global rather then per mesh
		totverts += len(m.verts)
	file.close()
	
	
	# Now we have all our materials, save them
	save_mtl(mtlfilename)
	
	print "obj export time: %.2f" % (sys.time() - time1)

Window.FileSelector(save_obj, 'Export Wavefront OBJ', newFName('obj'))

'''
TIME = sys.time()
import os
OBJDIR = '/obj_out/'
for scn in Scene.Get():
	scn.makeCurrent()
	obj = OBJDIR + scn.name
	print obj
	save_obj(obj)

print "TOTAL EXPORT TIME: ", sys.time() - TIME
'''

Thank you for the new script to try, but it didn’t work for me. Actually, it crashed, spitting out the following error to the console.

Traceback (most recent call last):
File “<string>”, line 269, in save_obj
TypeError: unhashable type
Using Python version 2.4

In the .obj file, it wrote the vertex coordinates, but nothing after that.

Oh no!!! When I upgraded from Blender 2.37a to 2.40, the .obj exporter changed its behavior so that it doesn’t export edges between vertices that don’t have faces attached. This is something that I really need, because I’m using line segments to define my track data for the racing game I am writing.

Please please let me know how to get that feature back. Now, when I export my track all I get is an empty file.

Removing line segments was probably done because it is a degenerate case, but if it doesn’t cause any problems otherwise would it be possible to put them back? Thanks so much.

Try the above script again… Ill add edge export to the next version.
Blender used to see edges as a face with 2 verts- changed in blender 2.4.

The normals still seem to be wrong. It’s funny that the different exporting was from Blender changing instead of the script. Your adding the edge exporting back will be a life saver.

Earlier, I posted a link to a .blend file that exhibits the problem I am talking about. It may help in your testing. I would like to help you with the script more, but I am unfamiliar with both Python and how it interfaces with Blender.