doc/doxygen/dot/x-architecture.gv

digraph arch_x {
    edge[
        fontname="DejaVu Sans",
        dir="both",
        arrowtail="dot",
        arrowsize=.5,
        fontname="DejaVu Sans",
        fontsize="18",
    ]

    node[
        shape="none",
        color=none,
        margin=0,
        fontname="DejaVu Sans",
        fontsize="18",
    ]

    {
        rank=same;
        c1 [label=<<TABLE STYLE="rounded" BGCOLOR="#ffbc00"><TR><TD>X Client</TD></TR></TABLE>>, URL="#c1"]
        c3 [label=<<TABLE STYLE="rounded" BGCOLOR="#ffbc00"><TR><TD>X Client</TD></TR></TABLE>>, URL="#c3"]
    }
    c2 [label=<<TABLE STYLE="rounded" BGCOLOR="#ffbc00"><TR><TD>X Client</TD></TR></TABLE>>, URL="#c2"]

    {
        rank=same;
        xserver [tooltip="X Server", label=<<TABLE STYLE="rounded" BGCOLOR="#ffbc00"><TR><TD><BR/>X Server<BR/><BR/></TD></TR></TABLE>>, URL="#xserver"]
        comp [tooltip="Compositor", label=<<TABLE STYLE="rounded" BGCOLOR="#ffbc00"><TR><TD><BR/>Compositor<BR/><BR/></TD></TR></TABLE>>, URL="#comp"]
    }

    impl [tooltip="KMS evdev Kernel", label=<<TABLE STYLE="rounded" BGCOLOR="#ffbc00"><TR><TD>KMS</TD><TD>evdev</TD></TR><TR><TD COLSPAN="2">Kernel</TD></TR></TABLE>>, URL="#impl"]

    c1 -> xserver [taillabel="③", labeldistance=2, URL="#step_3"];
    c2 -> xserver;
    c3 -> xserver;

    xserver -> c1 [taillabel="②", labeldistance=2, URL="#step_2"];
    xserver -> c2;
    xserver -> c3;

    xserver -> impl [taillabel="⑥", labeldistance=1.75, URL="#step_6"];
    xserver -> impl [style=invis, label="    "];
    impl -> xserver [taillabel="①", labeldistance=1.75, URL="#step_1"];

    xserver -> comp [style=invis];
    xserver -> comp [taillabel="④", labeldistance=1.75, labelangle=-45, URL="#step_4"];
    comp -> xserver [taillabel="⑤", URL="#step_5"];
    comp -> xserver [style=invis]

    c1 -> c2 [style=invis];
    c3 -> c2 [style=invis];
 }