Render arrowheads always horizontally

Help
1

I am playing around with Floorplan which uses graphviz under the hood and trying to figure out how to get this kind of edges. The edges seems cuved (spline=cuved/true) but the arrows are merged into one, they always start and end horizontally but can curve in the middle.
Here is an example from floorplan output:
here

I am trying to do this myself directly in graphviz (python) but no dice so far:
here
the edge arrows are at some kind of 45 degree angle

any suggestions are appreciated!

edit: just found an example on graphviz gallery, looks like i have to use dot engine and splines=true instead of curved… and rankdir=LR

[dot]

digraph g {
fontname="Helvetica,Arial,sans-serif"
node [fontname="Helvetica,Arial,sans-serif"]
edge [fontname="Helvetica,Arial,sans-serif"]
graph [
rankdir = "LR"
];
node [
fontsize = "16"
shape = "plaintext"
];
edge [
];
"node0" [
label = "<f0> 0x10ba8| <f1>"
shape = "record"
];
"node1" [
label = "<f0> 0xf7fc4380| <f1> | <f2> |-1"
shape = "record"
];
"node2" [
label = "<f0> 0xf7fc44b8| | |2"
shape = "record"
];
"node3" [
label = "<f0> 3.43322790286038071e-06|44.79998779296875|0"
shape = "record"
];
"node4" [
label = "<f0> 0xf7fc4380| <f1> | <f2> |2"
shape = "record"
];
"node5" [
label = "<f0> (nil)| | |-1"
shape = "record"
];
"node6" [
label = "<f0> 0xf7fc4380| <f1> | <f2> |1"
shape = "record"
];
"node7" [
label = "<f0> 0xf7fc4380| <f1> | <f2> |2"
shape = "record"
];
"node8" [
label = "<f0> (nil)| | |-1"
shape = "record"
];
"node9" [
label = "<f0> (nil)| | |-1"
shape = "record"
];
"node10" [
label = "<f0> (nil)| <f1> | <f2> |-1"
shape = "record"
];
"node11" [
label = "<f0> (nil)| <f1> | <f2> |-1"
shape = "record"
];
"node12" [
label = "<f0> 0xf7fc43e0| | |1"
shape = "record"
];
"node0":f0 -> "node1":f0 [
id = 0
];
"node0":f1 -> "node2":f0 [
id = 1
];
"node1":f0 -> "node3":f0 [
id = 2
];
"node1":f1 -> "node4":f0 [
id = 3
];
"node1":f2 -> "node5":f0 [
id = 4
];
"node4":f0 -> "node3":f0 [
id = 5
];
"node4":f1 -> "node6":f0 [
id = 6
];
"node4":f2 -> "node10":f0 [
id = 7
];
"node6":f0 -> "node3":f0 [
id = 8
];
"node6":f1 -> "node7":f0 [
id = 9
];
"node6":f2 -> "node9":f0 [
id = 10
];
"node7":f0 -> "node3":f0 [
id = 11
];
"node7":f1 -> "node1":f0 [
id = 12
];
"node7":f2 -> "node8":f0 [
id = 13
];
"node10":f1 -> "node11":f0 [
id = 14
];
"node10":f2 -> "node12":f0 [
id = 15
];
"node11":f2 -> "node1":f0 [
id = 16
];
}

[/dot]

2

That would be a cool feature. The spline router API already supports this and it’s used to make concentrators. Look for start.theta and end.theta in for example lib/common/splines.c (the layer that calls the basic spline router).

Someone noticed recently there was a hook in the graphviz grammar intended for setting the angle of edge endpoints, e.g.
a@0 -> b@180. This was never thought through or implemented. Anyway, the point isn’t to give absolute values - it’s to ask for horizontal or vertical slopes. This could also be controlled by an edge attribute. It seems like a nice little introductory intern-level project.

3
  • setting splines=ortho will guarantee (pretty sure) horizontal/vertical arrowheads
  • setting splines=false will guarantee a minimum of horizontal/vertical arrowheads
  • setting splines=true is so/so for horizontal/vertical arrowheads

@scnorth’s solution would provide this feature to all

Or you might be able to accomplish it with some Python post-processing code - the tail of an arrowhead is well defined, so tweaking that value and then getting the line itself to match up is doable. Hmmm.