Combining graph layout and edge labeling can either be done using generic labeling, or integrated labeling. Generic labeling means edge label placement that is performed as a postprocessing step after the actual graph layout has been calculated. Integrated labeling, in contrast, is directly provided by certain major layout algorithms as an integrated part of the layout calculation.

More on generic and integrated labeling can be found in the yFiles Developer's Guide: Automatic Label Placement.

Edge Label Setup for Automatic Placement

More on label models can be found in the yFiles Developer's Guide:

• Label Models
• Label Support

What the sample code snippet does:

• Creates an edge label and adds it early on to the edge realizer. If the edge realizer is properly associated an edge, and the edge in turn resides in a graph, this provides subsequently performed label settings access to the edge's proper environment.
• Sets the edge label's model. 'CENTER_SLIDER' has a dynamic number of label positions that lie on the edge's path.
• Sets the edge label's preferred placement to be close to the source node. Interface y.layout.LabelLayoutConstants defines a number of symbolic parameters for label positions, which are used by the automatic edge label placement algorithms.

// 'er' is of type y.view.EdgeRealizer. 

EdgeLabel el = er.createEdgeLabel();
er.addLabel(el);

el.setText("At the source side");

// Set an edge label model. 'CENTER_SLIDER' has a dynamic number of label 
// positions that lie on the edge's path.
el.setModel(EdgeLabel.CENTER_SLIDER);
// Choose a label position near the source node. 
el.setPreferredPlacement(LabelLayoutConstants.PLACE_AT_SOURCE);

Integrated Edge Labeling Capabilities

• Hierarchical: classes HierarchicLayouter, HierarchicGroupLayouter, and IncrementalHierarchicLayouter
• Orthogonal: class OrthogonalLayouter

setLabelLayouter(y.layout.LayoutStage)

setLabelLayouterEnabled(boolean)

What the sample code snippet does:

• Sets class y.layout.LabelLayoutTranslator as being responsible for automatic edge labeling. This specific setting is used to indicate that a graph layout algorithm's integrated edge labeling capabilities should be used. Actually, class LabelLayoutTranslator only converts label layout information so that it is understood by a graph layout algorithm.
• Explicitly enables automatic (edge) label placement.

// 'layout' is of type y.layout.Layouter. 

// Use integrated labeling support, and let class LabelLayoutTranslator do the 
// conversion of information held by an edge label's EdgeLabelLayout object 
// to data provider-based information that is understood by the algorithm. 
// (Either hierarchical or orthogonal layout.) 
layout.setLabelLayouter(new LabelLayoutTranslator());
layout.setLabelLayouterEnabled(true);

Refining Edge Label Positions

LabelLayoutDataRefinement

What the sample code snippet does:

• Instantiates a new LabelLayoutDataRefinement object that postprocesses edge label placement for certain edge labels.
• Tells the refinement process to also use (rather than completely ignore) label position candidates that overlap with other edge paths.
• Builds a composite layout stage that incorporates LabelLayoutTranslator and LabelLayoutDataRefinement.
• Sets the compound as being responsible for automatic edge labeling.
• Explicitly enables automatic (edge) label placement.

// Instantiate edge label position refinement postprocessing. 
LabelLayoutDataRefinement lldr = new LabelLayoutDataRefinement();
// As an option, the refinement process can be told to only penalize (rather than 
// completely ignore) label position candidates that overlap with other edge 
// paths. 
lldr.getInternalLabelingAlgorithm().setRemoveEdgeOverlaps(false);

// Create a layout stage that represents a composition of integrated labeling 
// with subsequent refinement on the calculated positions. 
CompositeLayoutStage cls = new CompositeLayoutStage();
cls.appendStage(new LabelLayoutTranslator());
cls.appendStage(lldr);

// Use the composed layout stage for automatic edge labeling. 
layout.setLabelLayouter(cls);
layout.setLabelLayouterEnabled(true);

Generic Labeling

What the sample code snippet does:

• Instantiates one of the available generic labeling algorithms and sets it as being responsible for automatic edge labeling.
• Explicitly enables automatic (edge) label placement.

// Instantiate a generic labeling algorithm. 
layout.setLabelLayouter(new GreedyMISLabeling());
layout.setLabelLayouterEnabled(true);

Improving Generic Labeling

y.layout.ProfitModel

LabelRanking

What the sample code snippet does:

• Instantiates a generic labeling algorithm.
• Tells the labeling algorithm to process only edge labels. (This is optional.)
• Sets class LabelRanking as the ProfitModel implementation to be used with this labeling algorithm.
• Sets the labeling algorithm as being responsible for automatic edge labeling.
• Explicitly enables automatic (edge) label placement.

// Instantiate a generic labeling algorithm. 
GreedyMISLabeling la = new GreedyMISLabeling();
// Process only edge labels. 
la.setPlaceNodeLabels(false);
la.setPlaceEdgeLabels(true);

// Set another ProfitModel to be used for rating label position candidates. 
la.setProfitModel(new LabelRanking());

layout.setLabelLayouter(la);
layout.setLabelLayouterEnabled(true);