How to control subgraphs' layout in dot?

Question

i have a digraph composed of many independant and simple subgraphs of various sizes. dot lays all these subgraphs horizontally, so i e

Answer 1

The steps to achieve this uses multiple graphviz tools which can be piped together.

The following line is a possible configuration, graph.dot being the file which contains your graph(s). You may have to fiddle with the options.

ccomps -x graph.dot | dot | gvpack -array3 | neato -Tpng -n2 -o graph.png

And here's the explanation:

---

1. Separate disconnected graphs

Tool: ccomps

decomposes graphs into their connected components

The -x option (Only the connected components are printed, as separate graphs) is probably all that is needed.

---

2. Layout each graph

Tool: dot

Each directed graph is layed out, one by one. This step is needed to get the position of the nodes and edges.

---

3. Pack all layed out graphs into one

Tool: gvpack

reads in a stream of graphs, combines the graphs into a single layout, and produces a single graph serving as the union of the input graphs.

You should read the documentation of the options for this tool and play with the options. For example, -array is used to lay out the graphs in a grid like manner, and offers several flags to control the layout.

---

4. Create the output

Tool: neato

The option -n2 tells neato to not layout the input graphs but to use the existing position attributes.

---

Example graph:

digraph G {
 subgraph G1 {
    a->{b; c;};
 }
 subgraph G2 {
    d -> {e; f;};
 }
 subgraph G3 {
    g -> h;
 }
 subgraph G4 {
    i -> j;
 }
 subgraph G5 {
    {k; l;} -> m;
 }
}

---

Edit: Sorting the digraphs in gvpack

In order to determine the order of appearance od the subgraphs in the combined layout created by gvpack, each subgraph will need a sortv attribute.

For example, the following graphs:

digraph G1 {
 sortv=1;
 a->{b; c;};
}
digraph G2 {
 sortv=2;
 d -> {e; f;};
}
digraph G3 {
 sortv=3;
 g -> h;
}
digraph G4 {
 sortv=4;
 i -> j;
}
digraph G5 {
 sortv=5;
 {k; l;} -> m;
}

can be transformed using

dot graph.dot | gvpack -array_u | neato -Tpng -n2 -o graph.png

resulting in