Connect GraphViz cluster to itself

Question

This answer describes how to connect GraphViz clusters to nodes and to other clusters.

I want to connect a cluster to itself, so the arrow exits the cluster boundary and re-enters (think of a state machine that has a transition to itself).

Below is an example:

digraph example {                                                               
    compound=true;                                                              
    "B" -> "C" [ltail="cluster_s0", lhead="cluster_s1", minlen=2];              
    "D" -> "C" [ltail="cluster_s1", lhead="cluster_s1", minlen=2];              
    subgraph cluster_s0 {                                                       
        "A" -> "B";                                                             
    }                                                                           
    subgraph cluster_s1 {                                                       
        "C" -> "D";                                                             
    }                                                                           
}

This throws warnings and draws the arrow inside the cluster instead of outside:

Here's a (very rough) sketch of what I want:

Is there a way to make GraphViz draw an arrow from D to C that exits and re-enters the cluster boundary like in the above example?

I think the only solution to this would be to have the D->C edge go through an intermediate, invisible node that's outside the cluster - but I've had no luck in getting it to position that node reasonably, so you end up with lines that snake all over the place rather than forming a simple arc. You can get a bit better result by specifying the edge as `"D":n -> "C":n` - the port directions turns the line into an arc that does go outside the cluster, but it still doesn't clip correctly. — jasonharper, Oct 09 '17 at 14:49

vaettchen · Answer 1 · 2017-10-10T12:24:42.147

1

I don't think that this is possible (and would eagerly wait for a fellow enthusiast to prove the contrary). In the meantime, would you consider a workaround using shape = record? My MWE

digraph example 
{                                                               
    rankdir = LR;

    node[ shape = record ];
    x   [ label = " { <a>A | <b>B } " ];
    y   [ label = " { <c>C | <d>D } " ];

    // edge
    x -> y;
    y:d:n -> y:c:n;
}

yields

Some work could be done to make it look a little more like your requirement but after all, it's a different animal.

edited Oct 10 '17 at 12:24

answered Oct 09 '17 at 13:27

vaettchen

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Unfortunately I need a solution that scales, as I will use it in complex scenarios with large graphs and many different node types and cluster sizes. – definelicht Oct 10 '17 at 11:28

score 1 · Answer 2 · answered Dec 29 '17 at 20:50

Here is another workaround it's a bit ugly though, basically you put some additional point nodes outside the subgraph and connect with edges without arrow head, also you probably want to connect them in reverse order to avoid strange impact on layout:

digraph example {      
    rankdir=LR                                                         
    compound=true;                                                              
    "B" -> "C" [ltail="cluster_s0", lhead="cluster_s1"];              
    "C" -> "DC1" [ltail="cluster_s1", dir=none];     
    DC1[shape=point]
    DC2[shape=point]
    DC1 -> DC2 [dir=none]
    "DC2" -> "D" [lhead="cluster_s1"];              
    subgraph cluster_s0 {                                                       
        "A" -> "B";                                                             
    }                                                                           
    subgraph cluster_s1 {                                                       
        "C" -> "D";         
    }                                                                           
}

You can improve the layout a bit by adding an invisible dummy node, but that probable don't scale (my guess is you will have difficulty determin when to add dummy nodes)

digraph example {      
    rankdir=LR                                                         
    compound=true;                                                              
    "B" -> "C" [ltail="cluster_s0", lhead="cluster_s1"];              
    "C" -> "DC1" [ltail="cluster_s1", dir=back];     
    DC1[shape=point]
    "DC2" -> "D" [lhead="cluster_s1"];              
    subgraph cluster_s0 {                                                       
        "A" -> "B";                                                             
    }                                                                           
    subgraph cluster_s1 {                                                       
        "C" -> "D";         
    }    
    DD[shape=point color=none]
    {D DC2}->DD[color=none]                                                                
}

Connect GraphViz cluster to itself

2 Answers2