preserve order if possible in wavefront

tests/test_export.py

@@ -164,6 +164,27 @@ def test_obj(self):
         assert m.metadata['vertex_texture'].shape == reconstructed.metadata[
             'vertex_texture'].shape
 
+    def test_obj_order(self):
+        """
+        Make sure simple round trips through Wavefront don't
+        reorder vertices.
+        """
+        # get a writeable temp file location
+        temp = g.tempfile.NamedTemporaryFile(
+            suffix='.obj',
+            delete=False)
+        temp.close()
+
+        # simple solid
+        x = g.trimesh.creation.icosahedron()
+        x.export(temp.name)
+        y = g.trimesh.load_mesh(temp.name, process=False)
+
+        # vertices should be same shape and order
+        assert g.np.allclose(x.vertices, y.vertices)
+        # faces should be same
+        assert g.np.allclose(x.faces, y.faces)
+
     def test_ply(self):
         m = g.get_mesh('machinist.XAML')
 

trimesh/io/wavefront.py

@@ -48,8 +48,21 @@ def append_mesh():
             # much as possible by sorting by remap key
             keys, values = (np.array(list(remap.keys())),
                             np.array(list(remap.values())))
+
+            try:
+                # if we sort keys as strings they will be an
+                # ordering like (1/1/1, 10/10/10) vs (1/1/1, 2/2/2)
+                # so try to convert to int before sorting
+                split = np.array([i.split('/')[0] for i in keys],
+                                 dtype=np.int)
+                order = split.argsort()
+            except BaseException:
+                # we can still use arbitrary order as a fallback
+                order = keys.argsort()
+
             # new order of vertices
-            vert_order = values[keys.argsort()]
+            vert_order = values[order]
+
             # we need to mask to preserve index relationship
             # between faces and vertices
             face_order = np.zeros(len(vertices),

trimesh/version.py

@@ -1 +1 @@
-__version__ = '2.35.14'
+__version__ = '2.35.15'