- self.uv_layers = [UvLayer(u) for u in self.uv_layers]
- self.uv_layers = sorted([u for u in self.uv_layers if not u.hidden], key=(lambda u: (u.unit or 1000, u.name)))
+ self.uv_layers = [UvLayer(u) for u in mesh.uv_layers]
+
+ # Assign texture unit numbers to UV layers that lack one
+ missing_unit = [u for u in self.uv_layers if u.unit is None]
+ if missing_unit:
+ missing_unit = sorted(missing_unit, key=(lambda u: u.name))
+ used_units = [u.unit for u in self.uv_layers if u.unit is not None]
+ for u, n in zip(missing_unit, (i for i in itertools.count() if i not in used_units)):
+ u.unit = n
+
+ self.uv_layers = sorted(self.uv_layers, key=(lambda u: u.unit))