Drawing a DAG

Question

I need advice on how to go about drawing a DAG (directional acyclic graph). Alot of stuff on the Internet about traversing a DAG and analyzing a DAG but I couldn't find any info about a algorithm to actually draw the graph. Anyone know any resources that can help ?

Answer 1

Try the following. You almost had it correct.
import java.awt.*;
import javax.swing.*;
import com.ibm.graph.*;
import com.ibm.graph.layout.*;
import com.ibm.graph.draw.*;
import com.ibm.graph.ext.visual.*;
import com.ibm.research.util.*;
import java.util.*;
public class GraphDraw  extends Canvas{
  private Graph graph;
  private int xOrigin = 200;
  private int yOrigin = 200;
  private int layout = 0;
  public GraphDraw(int layout)
    // create graph
    this.graph = new Graph();
    this.layout = layout;
  public void setup() {
    try {
      // set up the graph
      Vertex v1 = new Vertex();
      v1.setName("A");
      Vertex v2 = new Vertex();
      v2.setName("B");
      Vertex v3 = new Vertex();
      v3.setName("C");
      Vertex v4 = new Vertex();
      v4.setName("D");
      Edge e12 = new Edge(v1, v2);
      Edge e13 = new Edge(v1, v3);
      Edge e14 = new Edge(v1,v4);
      Edge e23 = new Edge(v2,v3);
      Edge e24 = new Edge(v2,v4);
      Edge e34 = new Edge(v3,v4);
      graph.add(v1);
      graph.add(v2);
      graph.add(v3);
      graph.add(v4);
      graph.add(e12);
      graph.add(e13);
      graph.add(e14);
      graph.add(e23);
      graph.add(e24);
      graph.add(e34);
      // tell graph how to lay itself out
      graph.setRoot(v1, true);
     if(layout==1)
       System.out.println("Using Glow97 layout");
       LayoutGlow97 manager = new LayoutGlow97();
       manager.setOptimalEdgeLength(100.0);
       manager.setRepulsionConstant(10.0);
       manager.setIterationsImproveVertexLocation(100);
       graph.setGraphLayoutManager(manager);
     } else {  // default layout
       System.out.println("Using DAG layout");
     // the set x and y of the root does not appear to work.
     // thats a bit strange, however a work around exists in the paint method
       LayoutDAG manager = new LayoutDAG();
       manager.setX0(xOrigin);
       manager.setY0(yOrigin);
       manager.setXSpaceMultiplier(2);
       manager.setYSpaceMultiplier(2);
       graph.setGraphLayoutManager(manager);
     // The following has to be done after the edges/vertices are added to the
     // graph. (does not work otherwise)
      // you were on the correct path here. Set up a method of drawing
     // say how graph will be drawn
     DrawNetEdgesThenVertices dn = new DrawNetEdgesThenVertices();    
     graph.setDrawable(dn);
     // say how vertices will be drawn
     Draw3VertexRectangleKeyText dv = new Draw3VertexRectangleKeyText();
     dv.setColorOutline(java.awt.Color.BLUE);
     graph.setDrawableVertices(graph,dv);
     // say how edges will be drawn
     Draw2EdgeLine de = new Draw2EdgeLine();
     de.setColorPath(java.awt.Color.RED);
     graph.setDrawableEdges(graph,de);
    graph.layout();
  } catch (Exception e) {
    e.printStackTrace();
this.setSize(600, 400);
this.setVisible(true);
public void paint (Graphics g) {
  try {
    super.paint(g);
    // quick hack to make the origin of the root work (translate the graphics to
    // the required offset) This may not work with other Layouts
    g.translate(xOrigin,yOrigin);
    graph.draw(g);
  } catch (Exception e) { e.printStackTrace(); }
public static void main(String[] args) {
  if(args.length!=1) {
    System.out.println("please enter a layout to use");
    System.exit(1); 
  int layout = 0;
  try{
    layout = Integer.parseInt(args[0]);
  }catch(NumberFormatException nfe) {
     System.out.println("Error. You did not enter an integer");
     System.exit(2);
  JFrame f = new JFrame();
  f.setSize(800,600);
  GraphDraw gd = new GraphDraw(layout);
  gd.setup();
  f.getContentPane().add(gd);
  f.show();
}The LayoutDAG layout method does not seem to honour the root positions
that you specify. Don't know why but the easy work around is to
translate the graphics context before you draw to it. (see the paint
method).
The Glow97 algorithm is a bit more tricky to use. It is an iterative
optimisation technique. This means that the graphics can appear almost
anywhere on the screen. So you will have to find where they are before
you attempt to draw them or they may well be off screen.
The Glow97 does allow you to refine the layout if you arn't satisfied.
I'm still trying to figure out the best way of drawing buttons instead
of vertices. It will probably involve subclassing one of the Draw?Vertex
classes to draw a button rather then a rectangle or oval.
matfud