Node and Label Placement in a Layered Layout Algorithm - About ...

3.3. ImplementationFigure 3.14. Some layout options for KLay Layered, especially the node placement selectionand some other relevant options.3.3.1 Implementation in the context of KLay LayeredBeing a part of the KLay Layered layout algorithm, the newly created node placerhas to be integrated into its source code structure. The choice of the right packagein the Java source tree is fortunately obvious, due to the clear structure of KLayLayered. Every phase of the algorithm, as listed in subsection 2.4.1, has its ownsub package. The new node placer is thus included in the package for phase four,de.cau.cs.kieler.klay.layered.p4nodes.The implementing class itself is called BKNodePlacer, in reference to the authorsof the basic approach, Ulrik Brandes and Boris Köpf. It extends AbstractAlgorithm,the abstract base class of algorithms in the KIELER project offering a reference tothe currently used progress monitor. The progress monitor can be used to give theuser visible feedback on the steps already done and steps to follow for the currenttask. Furthermore, the ILayoutPhase interface is implemented which is required byevery phase of the KLay Layered algorithm. It declares methods for the layout itselfand the required intermediate processors.This node placer can be chosen by the user via a so called layout option in theKIELER tool. The node placer has to be selected from a list of other implementationsfor phase four, as shown in Figure 3.14. Additionally, the results of the nodeplacement can also be influenced by these options. For example, a balanced orunbalanced layout can be chosen, or the minimum separation constraint δ (calledspacing in KIELER) can be changed.On the code level, the implementation has to differ slightly from the pseudocode given in Section 3.2. Normally, these differences are only small; for example,the position of a port in the graph data structure, the so called LGraph, is relative to49