_flat_faces([{Mat,Fs}|T], #sp{we=We}=Pd, Start0, Vs0, Fmap0, MatInfo0) ->     {Start,Vs,FaceMap} = flat_faces_0(Fs, We, Start0, Vs0, Fmap0),     MatInfo = [{Mat,?GL_QUADS,Start0,Start-Start0}|MatInfo0],     