Extremity constraints (HL)

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To force a node to the first level, you can specify:

layout.setSpecNodeLevelIndex(node, 0);

However, you cannot specify a level index for the last level because it is unknown at the beginning of layout how many levels are created. It is unwise to specify:

layout.setSpecNodeLevelIndex(node, java.lang.Integer.MAX_VALUE);

because it creates many empty levels between the levels used and the last one. Even though these empty levels are removed in postprocessing steps, it influences the speed and quality of the layout. (In fact, the algorithm runs out of memory if you set the specified level index unreasonably high.)

By using constraints you can achieve the same effect more efficiently.

To force a node to the first level:

In CSS

In the constraint file, specify:

ExtremityConstraint {
  node: node
  side: NORTH
}

In Java

In Java™ , call:

layout.addConstraint(
    new IlvExtremityConstraint(node, IlvHierarchicalLayout.NORTH));

To force a node to the last level:

In CSS

In the constraint file, specify:

ExtremityConstraint {
  node: node
  side: SOUTH
}

In Java

Call:

layout.addConstraint(
    new IlvExtremityConstraint(node, IlvHierarchicalLayout.SOUTH));

With compass directions as a convenient reference (see Port sides parameter (HL)), the first level indicates the north pole and the last level indicates the south pole. You can also specify extremity constraints for the east and west sides:

layout.addConstraint(
    new IlvExtremityConstraint (node1, IlvHierarchicalLayout.EAST));
layout.addConstraint(
    new IlvExtremityConstraint (node2, IlvHierarchicalLayout.WEST));

The west extremity constraint forces the node to the lowest position index within its level, and the east extremity constraint forces the node to the highest position index within its level. The position indexes specify the relative position within the level. For instance, a node with west extremity constraint is the leftmost node within its level, if the flow direction is towards the bottom. However, it does not affect other levels; there can be a node in another level that is still placed farther to the left.

The following figure illustrates some extremity constraints.

Example
of Hierarchical Layout illustrating the extremity contraint

Sketch of Extremity Constraints

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Hierarchical Layout (HL)