Prefuse : Adding edge weights to the GraphView Demo

Question

I am using the prefuse visualization toolkit, The GraphView Demo in the toolkit is amazing providing a variety of controls to visualize the data.

I am able to generate GraphML for my dataset and visualize it using GraphView, One additional thing that i would love to have is to label the edges with weights or color coding to demonstrate the strength between two nodes.

Any input about the same are greatly appreciated..Thanks..

Answer 1

Disclaimer: I haven't worked with the API just checked the documentation:) It seems that the API has an EdgeRenderer interface that you should implement to achieve the desired behaviour.

Ref: http://prefuse.org/doc/manual/introduction/example/, http://prefuse.org/doc/api/prefuse/render/DefaultRendererFactory.html

Update: First a correction: in fact EdgeRenderer is not an iterface but a class. I've made a simple demo to illustrate how to implement custom edge rendering.

Feature

Add label to edges containing the initials of the node labels

Method

I made a quick and dirty solution, that is copied LabelRenderer and modified in order to handle edges.

Code

I named the class as MyEdgeRenderer:

public class MyEdgeRenderer extends AbstractShapeRenderer {

use the original EdgeRenderer to draw edge lines (see render() below for the renderer in action):

protected EdgeRenderer m_edgeRenderer = new EdgeRenderer();

modify getText() to get the initials from nodes:

protected String getText(VisualItem item) {
    EdgeItem edge = (EdgeItem)item;
    VisualItem item1 = edge.getSourceItem();
    VisualItem item2 = edge.getTargetItem();    

    String t1 = null, t2 = null;
    if ( item1.canGetString(m_labelName) ) {
        t1 = item1.getString(m_labelName).substring(0,1);            
    };
    if ( item2.canGetString(m_labelName) ) {
        t2 = item2.getString(m_labelName).substring(0,1);            
    };
    if (t1 != null && t2 != null)
        return t1 + "-" + t2;
    else
        return null;
}

modified getAlignedPoint() to position the label half way on the edge:

protected void getAlignedPoint(Point2D p, VisualItem item, 
        double w, double h, int xAlign, int yAlign)
{
    double x=0, y=0;                

    EdgeItem edge = (EdgeItem)item;
    VisualItem item1 = edge.getSourceItem();
    VisualItem item2 = edge.getTargetItem();

    // label is positioned to the center of the edge
    x = (item1.getX()+item2.getX())/2;
    y = (item1.getY()+item2.getY())/2;      
    ...

modify render() to (I) first draw the line and (II) use black color:

public void render(Graphics2D g, VisualItem item) {         
    m_edgeRenderer.render(g, item);
    ...

    // render text
    int textColor = ColorLib.color(Color.BLACK); // item.getTextColor() 
    if ( text != null && ColorLib.alpha(textColor) > 0 ) {
    ...

For testing I modified the sample found on the Prefuse website (http://prefuse.org/doc/manual/introduction/example/Example.java):

    // -- 3. the renderers and renderer factory ---------------------------

    // draw the "name" label for NodeItems
    LabelRenderer ir = new LabelRenderer("name");
    ir.setRoundedCorner(8, 8); // round the corners

    // draw the "name" initials for EdgeItems
    MyEdgeRenderer er = new MyEdgeRenderer("name");
    er.setRoundedCorner(8, 8); // round the corners

    // create a new default renderer factory
    // return our name label renderer as the default for all non-EdgeItems
    // includes straight line edges for EdgeItems by default
    vis.setRendererFactory(new DefaultRendererFactory(ir, er));

This is just a demo to illustrate custom rendering. In real you would probably retrieve label text and color from the graph model, ie: EdgeItem.getString(), getTextColor(). I guess both attribute could come from the GraphML data. Also the example code shows how to set colors for nodes, it might be adapted for edges as well (though I haven't tried):

    // -- 4. the processing actions ---------------------------------------
    ...
    // use black for node text
    ColorAction text = new ColorAction("graph.nodes",
            VisualItem.TEXTCOLOR, ColorLib.gray(0));