Mathematica GraphPlot and the EdgeRenderingFunction

Question

While I'm waiting for the sorting to finish, I would like to adjust a part of Mathematica graph I'm working on. The problem is that nodes are on top of edges, I wonder if there is a way to reverse that. In the image you can see that arrows are not showing proper...

I'm doing a GraphPlot[] with custom VertexRenderingFunction and EdgeRenderingFunction paramaters. It looks something like this:

As you can see, it would be as they say cool if the arrows were on top of the nodes. Is there an easy way to hax it in?

Answer 1

I don't know if there is a way to do this directly with GraphPlot options or not but you could manipulate the Graphics object produced by GraphPlot directly. For example, here's a graph whose features are similar to yours.

bg = GraphPlot[Table[i -> Mod[3 i + 1, 9],
  {i, 0, 8}], DirectedEdges -> True,
  VertexRenderingFunction -> (
  {{White, Disk[#, 0.15]}, Circle[#, 0.15]} &),
  EdgeRenderingFunction -> (Arrow[#1] &)]

You can examine the structure of the Graphics primitives and directives as follows:

  bg // InputForm

You can see that the arrows are placed down before the vertices. Simply reverse this as follows.

  MapAt[Reverse, bg, {1, 1}]

Of course, your Graphics object will likely have a different structure.

Mark McClure

Answer 2

Mark's answer does exactly what you asked for -- and you could write your own function that automates the Reverse.

A less direct solution might be to just draw the arrow heads back from the end a little:

GraphPlot[Table[i -> Mod[3 i + 1, 9], {i, 0, 8}], 
 VertexRenderingFunction -> ({{White, Disk[#, 0.15]}, 
     Circle[#, 0.15]} &), DirectedEdges -> True, 
 EdgeRenderingFunction -> ({Arrowheads[{{.05, .8}}], Red, 
     Arrow[#]} &)]

This would also reduce the congestion at the nodes.