Interactive Constraint Generation

As discussed earlier the IPSep-CoLa layout algorithm presented in [24] improves on the force-directed layout model by the addition of separation constraints. These constraints force the algorithm to layout the graph according the the placing and solving of equality/inequality equations. In an interactive context it is necessary to provide the following functionality within the editor.

1. Receive constraint input from the user.
2. Display the constraints in the editor to provide feedback to the user.
3. Convert the internal constraint model to equality/inequality separation constraints for IPSep-CoLa.

The tool used to implement this functionality is an interactive diagramming tool called Dunnart[16]. Dunnart was developed by Wybrow to investigate user interface and human-computer interaction issues for constraint based diagram creation and editing.

Figure: The process of laying out a graph in Dunnart with IPSep-CoLa.

The process of receiving constraint input from the user differs between the different constraint options, but the general architecture of the layout process is shown in Fig. . The diagram was drawn in Dunnart and uses directed edge constraints as discussed later. An example showing how constraints are generated and used in the layout process will be examined next through the use of containment constraints.