Question

I want to draw two parallel horizontal lines at the top. How to do it?
My code is here. The output lines are of the same height, so it does not work.

digraph G {

    graph [center, rankdir=TB, bgcolor=black];
    edge [arrowsize=1, color=red, dir=none];

    node [penwidth=1, color=white, fontcolor=white, labelloc=b];

    BB1P1[shape=point, color=red, width=0.01];
    BB1P[shape=point, color=white, width=0.1];
    BB1PV[shape=point, color=red, width=0.01];
    BB1P2[shape=point, color=red, width=0.01];

    BB1P1 -> BB1P -> BB1PV -> BB1P2;

    BB2P1[shape=point, color=red, width=0.01];
    BB2PV[shape=point, color=red, width=0.01];
    BB2P[shape=point, color=white, width=0.1];
    BB2P2[shape=point, color=red, width=0.01];

    BB2P1 -> BB2PV -> BB2P -> BB2P2;

    { rank=same; BB1P1; BB1P; BB1PV; BB1P2 };
    { rank=same; BB2P1; BB2PV; BB2P; BB2P2 };

}

Answer 1

Actually one invisible node is sufficient:

digraph G {
    graph [center, rankdir=TB, bgcolor=black];
    edge [arrowsize=1, color=red, dir=none];

    node [penwidth=1, color=red, fontcolor=white, labelloc=b, shape=point, width=0.01];

    {
        rank=same;
        BB1P1;
        BB1P[color=white, width=0.1];
        BB1PV;
        BB1P2;
    }

    {
        rank=same;
        BB2P1;
        BB2PV;
        BB2P[color=white, width=0.1];
        BB2P2;
    }

    BB1P1 -> BB1P -> BB1PV -> BB1P2;
    BB2P1 -> BB2PV -> BB2P -> BB2P2;
    BB1P1 -> BB2P1[style=invis]; 
}

Or, even simpler, just change rankdir to LR:

digraph G {
    graph [center, rankdir=LR, bgcolor=black];
    edge [arrowsize=1, color=red, dir=none];

    node [penwidth=1, color=red, fontcolor=white, labelloc=b, shape=point, width=0.01];

    BB1P[color=white, width=0.1];
    BB2P[color=white, width=0.1];

    BB1P1 -> BB1P -> BB1PV -> BB1P2;
    BB2P1 -> BB2PV -> BB2P -> BB2P2;
}