A sample custom layout algorithm

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If the layout algorithms provided with Rogue Wave® JViews Diagrammer do not meet your needs, you can develop your own layout algorithms by subclassing IlvGraphLayout.

When a subclass of IlvGraphLayout is created, it automatically fits into the generic Rogue Wave JViews Diagrammer layout framework and benefits from its infrastructure:

Generic parameters: see Base class parameters and features
Notification of progress: see Using event listeners
Capability to lay out any graph object using the generic graph model: see Using the graph model
Capability to apply the layout separately for the connected components of a disconnected graph: see Laying out connected components of a disconnected graph
Capability to lay out nested graphs (see Nested layouts), and so on.

Example

To illustrate the basic ideas for defining a new layout, the following simple example shows a possible implementation of the simplest layout algorithm, the Random Layout. The new layout class is called MyRandomLayout .

The following code shows the skeleton of the class:

public class MyRandomLayout
  extends IlvGraphLayout
{
  public MyRandomLayout()
  {
  }

  public MyRandomLayout(MyRandomLayout source)
  {
    super.source(source);
  }

  public IlvGraphLayout copy()
  {
    return new MyRandomLayout(this);
  }

  protected void layout(boolean redraw)
  {
    ...
  }
}

The constructor with no arguments is empty.

The copy constructor and the copy method are implemented, because they are used when laying out a nested graph (see Nested layouts).

Then, the abstract method layout(boolean) of the base class is implemented as follows:

 protected void layout(boolean redraw) 
  { 
    // obtain the graph model
    IlvGraphModel graphModel = getGraphModel();
 
    // obtain the layout report 
    IlvGraphLayoutReport layoutReport = getLayoutReport(); 
 
    // obtain the layout region 
    IlvRect rect = getCalcLayoutRegion(); 
    float xMin = rect.x; 
    float yMin = rect.y; 
    float xMax = rect.x + rect.width; 
    float yMax = rect.y + rect.height; 
 
    // initialize the random generator 
    Random random = (isUseSeedValueForRandomGenerator()) ? 
        new Random(getSeedValueForRandomGenerator()) :
        new Random(); 
 
    // browse the objects in the grapher 
    Enumeration nodes = graphModel.getNodes(); 
    while (nodes.hasMoreElements()) { 
        Object node = nodes.nextElement(); 
 
        // skip fixed nodes
        if (isPreserveFixedNodes() && isFixed(node)))
            continue; 
 
        // compute coordinates 
        float x = xMin + (xMax - xMin) * random.nextFloat(); 
        float y = yMin + (yMax - yMin) * random.nextFloat(); 
 
        // move the node to the computed position 
        graphModel.moveNode(node, x, y, redraw); 
 
        // notify listeners on layout events 
        callLayoutStepPerformedIfNeeded(); 
    } 
 
    // set the layout report code 
    layoutReport.setCode(IlvGraphLayoutReport.LAYOUT_DONE); 
} 
...

The layout method is protected , which is the access type of the method in the base class. This does not prevent a user outside the package that contains the class from performing the layout, because it is started by using the public method performLayout .

Current section

Defining your own type of layout