Straight edge between clusters in Graphviz

Question

I'm trying to have an edge between clusters in Graphviz where the edge does not affect the ranking.

This looks fine:

digraph {
  subgraph clusterX {
    A    
    B
  }

  subgraph clusterY {
    C
    D
  } 

  A -> B
  B -> C [constraint=false]
  C -> D
}

However when I add a label to the C -> D edge the B -> C edge tries to circumvent said label (which looks ugly).

digraph {
  subgraph clusterX {
    A    
    B
  }

  subgraph clusterY {
    C
    D
  } 

  A -> B
  B -> C [constraint=false]
  C -> D [label=yadda]
}

Any idea how I can keep the edge from B to C straight?

Answer 1

You can use this version :

digraph G { 
  subgraph cluster_X {
    A [ pos = "0,1!" ]; 
    B [ pos = "0,0!" ];
  } 
  subgraph cluster_Y {
    C [ pos = "1,1!" ]; 
    D [ pos = "1,0!" ];
  } 
  A -> B
  B -> C[label="yadda"]
  C -> D;
}

Then you use neato (not dot)

neato -Tpng -oyadda.png yadda.dot

And the result is :

Answer 2

The easiest way to achieve this is to add splines=false to the dot file - this forces the rendering of the edges to be straight lines:

digraph {
 splines=false;
 subgraph clusterX {
    A;
    B;
 }

 subgraph clusterY {
    C;
    D;
 } 

 A -> B;
 B -> C [constraint=false];
 C -> D [label=yadda];
}

Output:

Answer 3

Instead of the label attribute, you can use the attributes xlabel or headlbel or taillabel.

• Result with xlabel:
  
  Script:

  digraph {
      subgraph clusterX { A B }
      subgraph clusterY { C D } 
      A -> B
      B -> C [constraint=false]
      C -> D [xlabel=yadda]
  }
  

• Result with headlabel:
  
  Script:

  digraph {
      subgraph clusterX { A B }
      subgraph clusterY { C D } 
      A -> B
      B -> C [constraint=false]
      C -> D [headlabel=yadda]
  }
  

• Result with taillabel:
  
  Script:

  digraph {
      subgraph clusterX { A B }
      subgraph clusterY { C D } 
      A -> B
      B -> C [constraint=false]
      C -> D [taillabel=yadda]
  }