my $cube = [
    [-0.5, 0.5, 0.5],[ 0.5, 0.5, 0.5],[ 0.5,-0.5, 0.5],[-0.5,-0.5, 0.5], # front face 
    [-0.5, 0.5,-0.5],[ 0.5, 0.5,-0.5],[ 0.5,-0.5,-0.5],[-0.5,-0.5,-0.5], # back face
];