public static extern int GvRenderData(GraphvizHandle gvc, CgraphHandle cgraph, string format, out IntPtr result, out int length);
public static extern int GvFreeLayout(GraphvizHandle gvc, CgraphHandle cgraph);
public static extern IntPtr GvcBuildDate(GraphvizHandle gvc);
public static extern int GvLayout(GraphvizHandle gvc, CgraphHandle cgraph, string engine);
public static extern IntPtr GvcVersion(GraphvizHandle gvc);