code: def fix_normals(mesh, multibody=False):
      
      # traverse face adjacency to correct winding
      fix_winding(mesh)
      # check to see if a mesh is inverted
      fix_inversion(mesh, multibody=multibody)
docs: Fix the winding and direction of a mesh face and
      face normals in-place.
  
      Really only meaningful on watertight meshes, but will orient all
      faces and winding in a uniform way for non-watertight face
      patches as well.
  
      Parameters
      -------------
      mesh:      Trimesh object
      multibody: bool, if True try to correct normals direction
                       on every body.
  
      Alters
      --------------
      mesh.faces: will flip columns on inverted faces