Nesting nodes in GraphViz - graphviz

Question

I'm trying to draw bigraphs in GraphViz (something like this)
Is it possible to nest nodes directly in GraphViz?
If not is it possible to change the shape of a subgraph/cluster?
I have found a post about how to import images of graphs into nodes but that seems like more effort than drawing them in powerpoint.
I can also make clusters visible, but they will include nodes from outside the cluster and as far as I can tell have a fixed shape.
Thanks for your help.

Answer 1

Nest nodes is impossible, but nest clusters is possible.
Subgraph/cluster has some predefined styles. Also nodes has predefines shapes. I don't know about manual editing path of border shapes for nodes in graphviz in different layouts (or alternatives like representing the border as a chain of nodes), maybe someone else can tell us.
You can get nested nodes in neato layout engine, but in fact they will be nested only visually, because you just set their coordinates with pos attribute, which means they overlap each other.
Example image:
and script:
graph {
layout=neato
node [shape=circle pin=true ]
foo [height=0.6 pos="0.7,1.5" ]
bar [height=2 pos="1,2" ]
baz [height=1 pos="2,2" ]
}
You can import images as backgrounds into nodes as described in this answer. For example for Windows you can use this official archive, it comes with a cairo.dll, which will avoid errors like Warning: No loadimage plugin for "jpeg:cairo" when you run the command $ dot -Tpng input.dot -o output.png.
The image from your question can be drawn like this:
Script:
digraph {
graph [
layout=dot,
ranksep=1,
overlap=false,
compound=true, // to enable `lhead`, `ltail` features
newrank=true, // to enable ranking between nodes in clusters
splines=true,
splines=curved]
edge[color=lime arrowhead=none]
node[shape=plaintext]
y0 [label=<<FONT><I>y</I><SUB>0</SUB></FONT>>]
y1 [label=<<FONT><I>y</I><SUB>1</SUB></FONT>>]
y2 [label=<<FONT><I>y</I><SUB>2</SUB></FONT>>]
x0 [label=<<FONT><I>x</I><SUB>0</SUB></FONT>>]
x1 [label=<<FONT><I>x</I><SUB>1</SUB></FONT>>]
subgraph cluster_r0{
style="rounded, dashed"
margin=20
label=<<FONT><I>r</I><SUB>0</SUB></FONT>>
v2 [shape=circle]
noname_dot[shape=point height=0]
subgraph cluster_v0{
style="rounded"
label=<<FONT><I>v</I><SUB>0</SUB></FONT>>
invis_dot_1 [style=invis shape=point]
subgraph cluster_v1{
style="rounded";
label=<<FONT><I>v</I><SUB>1</SUB></FONT>>
subgraph cluster_s0{
label=<<FONT><I>s</I><SUB>0</SUB></FONT>>
fillcolor=lightgrey
style="filled, rounded"
invis_dot_2 [style=invis shape=point]
}
}
}
}
y0 -> noname_dot
noname_dot -> invis_dot_2 [lhead="cluster_v1"]
noname_dot -> invis_dot_1 [lhead="cluster_v0"]
noname_dot -> v2 [constraint=false]
y1 -> v2
subgraph cluster_r1{
style="rounded, dashed"
margin=20
label=<<FONT><I>r</I><SUB>1</SUB></FONT>>
noname_dot_2 [shape=point height=0]
subgraph cluster_s3{
label=<<FONT><I>s</I><SUB>3</SUB></FONT>>
fillcolor=lightgrey
style="filled, rounded"
invis_dot_s3 [style=invis shape=point]
}
subgraph cluster_v3{
style="rounded"
label=<<FONT><I>v</I><SUB>3</SUB></FONT>>
subgraph cluster_s2{
label=<<FONT><I>s</I><SUB>2</SUB></FONT>>
fillcolor=lightgrey
style="filled, rounded"
invis_dot_s2 [style=invis shape=point]
}
}
}
y2 -> noname_dot_2
noname_dot_2 -> x0
v2 -> noname_dot_2 [weight=0]
noname_dot_2 -> invis_dot_s2 [lhead="cluster_v3"]
invis_dot_s2 -> x1 [ltail="cluster_v3"]
// Vertical alignment (`rank`) of the desired nodes:
{rank=same; noname_dot; noname_dot_2; v2 }
{rank=same; invis_dot_s3; invis_dot_s2 }
{rank=same; x0; x1;}
{rank=same; y0; y1; y2;}
}