Getting position of nodes in graphviz

Question

I am using graphviz as library in C#. I found a solution that helps importing functions from gvc.dll and cgraph.dll here.

What I want to do is to get position of nodes in my rendered graph. After researching in library guide I used this solution in RenderImage function:

if (gvLayout(gvc, g, layout) != SUCCESS)
    throw new Exception("Layout failed.");
if (gvRender(gvc, g, "dot", IntPtr.Zero) != SUCCESS)
    throw new Exception("Render failed.");

IntPtr np = agnode(g, "1", 0);
if (np == IntPtr.Zero)
    throw new Exception("Node not found.");
string pos = agget(np, "pos");

I defined agget function as follows:

[DllImport(LIB_GRAPH, CallingConvention = CallingConvention.Cdecl)]
public static extern string agget(IntPtr node, string attribute);

Everything seems fine, however after executing agget function, the debugging is aborted with infromation: the execution process exited unexpectedly. But no exception was thrown.

What is wrong with my code? Maybe I could use macro like: ND_pos? But I couldn't find it and I don't know how to declare it (use DllImport) in C#. Or maybe after rendering graph I can retrieve the information from dot file? If so, how can I do it?

Answer 1

I manged to solve it using gvRenderFile. I export rendered dot file to another dot file, and I read from it.

if (gvRenderFilename(gvc, g, "dot", path) != SUCCESS)
    throw new Exception("Render failed.");
string text = File.ReadAllText(path);