Question

I am building a .dot file to represent a directed acyclic graph.

I need to generate an image from this graph.dot file (using C#) so that I can show the image in a Picture Box in my application. What library should I use?

Using GraphViz’s command in the command prompt:

dot -Tpng graph.dot -o graph.png 

I am able to generate the image fine, so I know that the formatting of my .dot file is correct.

Thank you.

Answer 1

Thank you @marapet for pointing me to David Brown’s project.

I have downloaded the sample at: David Brown’s Implicit Operator

The sample works well.

I copied the required code to my project. I had to change my .NET Target Framework from 4.0 to 3.5, but that isn’t a problem.

So far, the code has never crashed. (Even though other people have reported issues.)

UPDATE

David Brown’s website seems to be down so I have updated this answer with the code I’d taken from the website.

//Code for this Class downloaded from http://implicitoperator.com/blog/2010/4/11/graphviz-c-sample.html

public class GraphViz
{

    public const string LIB_GVC = "gvc.dll";
    public const string LIB_GRAPH = "graph.dll";
    public const int SUCCESS = 0;

    /// <summary> 
    /// Creates a new Graphviz context. 
    /// </summary> 
    [DllImport(LIB_GVC)]
    public static extern IntPtr gvContext();

    /// <summary> 
    /// Reads a graph from a string. 
    /// </summary> 
    [DllImport(LIB_GRAPH)]
    public static extern IntPtr agmemread(string data);

    /// <summary> 
    /// Renders a graph in memory. 
    /// </summary> 
    [DllImport(LIB_GVC)]
    public static extern int gvRenderData(IntPtr gvc, IntPtr g,
        string format, out IntPtr result, out int length);

    /// <summary> 
    /// Applies a layout to a graph using the given engine. 
    /// </summary> 
    [DllImport(LIB_GVC)]
    public static extern int gvLayout(IntPtr gvc, IntPtr g, string engine);

    /// <summary> 
    /// Releases the resources used by a layout. 
    /// </summary> 
    [DllImport(LIB_GVC)]
    public static extern int gvFreeLayout(IntPtr gvc, IntPtr g);

    /// <summary> 
    /// Releases a context's resources. 
    /// </summary> 
    [DllImport(LIB_GVC)]
    public static extern int gvFreeContext(IntPtr gvc);

    /// <summary> 
    /// Releases the resources used by a graph. 
    /// </summary> 
    [DllImport(LIB_GRAPH)]
    public static extern void agclose(IntPtr g);

    public static Image RenderImage(string source, string layout, string format)
    {
        // Create a Graphviz context 
        IntPtr gvc = gvContext();
        if (gvc == IntPtr.Zero)
            throw new Exception("Failed to create Graphviz context.");

        // Load the DOT data into a graph 
        IntPtr g = agmemread(source);
        if (g == IntPtr.Zero)
            throw new Exception("Failed to create graph from source. Check for syntax errors.");

        // Apply a layout 
        if (gvLayout(gvc, g, layout) != SUCCESS)
            throw new Exception("Layout failed.");

        IntPtr result;
        int length;

        // Render the graph 
        if (gvRenderData(gvc, g, format, out result, out length) != SUCCESS)
            throw new Exception("Render failed.");

        // Create an array to hold the rendered graph
        byte[] bytes = new byte[length];

        // Copy the image from the IntPtr 
        Marshal.Copy(result, bytes, 0, length);

        // Free up the resources 
        gvFreeLayout(gvc, g);
        agclose(g);
        gvFreeContext(gvc);

        using (MemoryStream stream = new MemoryStream(bytes))
        {
            return Image.FromStream(stream);
        }
    }
}