如何防止 Graphviz 移动节点以容纳边缘

Question

I'm trying to reproduce the following figure using Graphviz:

Here's what I came up with so far:

digraph
{
  rankdir="LR";
  splines=polyline;

  b [shape=circle, label="", style=filled, color=gray, width=0.2, height=0.2];
  c [shape=box, label="C(s)", style=filled, color=gray, xlabel=controller];
  d [shape=box, label="P(s)", style=filled, color=gray, xlabel=plant];
  a [shape=point, color=transparent, label="a"];
  e [shape=point, color=transparent, label="e"];
  f [shape=point, color=transparent, label="f"];

  c -> d [label="u"]
  b -> c [label="e"]
  a -> b [label="r"]
  d -> e [dir=none]
  e -> f [label="y"]
  e -> b
}

This gets me close but not quite there yet, as dot seems to move the nodes to accomodate the edge from e to b and not the other way round:

How do I get it so that the edge from e to b bends around the nodes rather than displacing them?

Answer 1

(lots of trial-and-error)

• used html records to contrail external label positioning
• constraint=false & dir=back for e->b edge
• turned off edge clipping as needed to improve edges

digraph {
  // lines were rearranged just to simplify my comprehension
  rankdir="LR";
  splines=polyline;
  //splines=ortho;  // might work, if edges use xlabels
 
  a [shape=point, color=transparent, label="a"];
  b [shape=circle, label="", style=filled, fillcolor=gray, width=0.2, height=0.2];

  // c & d use html tables to better position exterior labels
  c [shape=plaintext label=<<TABLE BORDER="0" >
    <TR>   <TD>controller</TD>   </TR>
    <TR>   <TD border="1" port="p0" bgcolor="grey">C(s)</TD>   </TR>
    </TABLE>>];

  d [shape=plaintext label=<<TABLE BORDER="0">
    <TR>   <TD>plant</TD>   </TR>
    <TR>   <TD border="1" port="p0" bgcolor="grey">C(s)</TD>   </TR>
    </TABLE>>];
  
  e [shape=point width=.01 label=""];
  f [shape=point width=.00  label="" color=white];

  a -> b [label="r"]
  b -> c:p0 [label="e"]
  c:p0:e -> d:p0:w [label="u"]
  d:p0 -> e [dir=none headclip=false]
  e -> f [label="y" tailclip=false headclip=false]

  b -> e [dir=back constraint=false]
}

Giving:

Answer 2

Based on the above, wouldn't changing:

  e -> b

into

  e -> b [dir=none constraint=false]

ie

digraph
{
  rankdir="LR";
  splines=polyline;

  b [shape=circle, label="", style=filled, color=gray, width=0.2, height=0.2];
  c [shape=box, label="C(s)", style=filled, color=gray, xlabel=controller];
  d [shape=box, label="P(s)", style=filled, color=gray, xlabel=plant];
  a [shape=point, color=transparent, label="a"];
  e [shape=point, color=transparent, label="e"];
  f [shape=point, color=transparent, label="f"];

  c -> d [label="u"]
  b -> c [label="e"]
  a -> b [label="r"]
  d -> e [dir=none]
  e -> f [label="y"]
  e -> b [dir=none constraint=false]
}

as on: http://www.webgraphviz.com/

I get:

(Disadvantage we still have a small gap at the line labeled y ).