Segment operations

Complete or incomplete segment tree

Each end of a hyperedge has a segment that is directly incident to the hyperedge end. You can obtain this segment by calling:

seghyperedge.getEndSegment(hyperedgeEnd);

The segment tree is complete, if each end of the hyperedge is reachable from each other end through a segment traversal. See the method visit in section Method for traversal of incident segments in any direction.

If this is not the case, the segment tree is incomplete. For example, you have a disconnected forest of segment trees.

To test whether a segment tree is complete, call:

seghyperedge.isSegmentSetComplete();

Hyperedges with incomplete segment trees can be displayed. Incomplete segment trees look wrong when displayed. They do not convey information on which nodes are connected by the hyperedge. Therefore, you are usually interested only in complete segment trees.

The API of IlvSegmentedHyperEdge is flexible enough to allow incomplete segment trees, which simplifies the task of restructuring the segments of a hyperedge.

The segment tree can be made incomplete temporarily, but for the final drawing you are recommended to make the segment tree complete.

Therefore, it is necessary to distinguish between primitive segment operations and safe segment operations.

Primitive operations can make the segment tree incomplete.

Safe segment operations, when applied to a complete segment tree, result in a complete segment tree.

Primitive segment operations

The API on IlvSegmentedHyperEdge.Segment allows you to query the information of the segment, but not to manipulate the segments. The manipulation must be done by the API on the hyperedge itself. Any manipulation of the segment tree may change the bounding box of the hyperedge. Therefore, an applyToObject session is usually necessary.

The following primitive segment operations allow you to change the segment tree so that it becomes incomplete. The API of IlvSegmentedHyperEdge includes the methods listed in the following table.

Methods of IlvSegmentedHyperEdge for making the segment tree incomplete

Method	Description
addSegment	Creates a new segment that is incident to the hyperedge end. The new segment has a fixed angle.
addSegment	Creates a new segment that is incident to the hyperedge end. The new segment has a variable angle. As long as the segment is not terminated by any other segment, it uses the point (x, y) as the other termination point of the segment.
addSegment	Creates a new segment that is incident to both hyperedge ends. The new segment has a variable angle.
addSegment	Creates a new segment that is incident to the existing segment. The new segment has a fixed angle. The input point (x,y) determines the position of the segment.
addSegment	Creates a new segment that is incident to the existing segment. The new segment has a variable angle. The input points (x1,y1) and (x2,y2) determine the start and end coordinates of the new segment.
removeSegment	Removes a segment from the segment tree. This makes the segment tree incomplete. Returns the segments that were formerly incident to the removed segment.
connectSegments	Connects two segments so that they become incident. It is not possible to connect segments in a way that would form a cycle in the segment tree. The constraints on variable and fixed angle segments must be observed.
disconnectSegments	Disconnects two segments so that they are no longer incident. This makes the segment tree incomplete.
isConnected	Tests whether two segments are connected.

Safe segment operations

When hyperedge ends are added to or removed from the hyperedge, the segment tree must change to remain complete. The hyperedge has an autoconnect mode that does this automatically.

The following code example shows how to keep the segment tree complete.

Keeping the segment tree complete

IlvSegmentedHyperEdge seghyperedge = ...
seghyperedge.setAutoConnect(true);
// ... this will add segments automatically as necessary
seghyperedge.addFrom(node);
seghyperedge.addTo(node);
// ... now the segment tree is complete
// seghyperedge.isSegmentSetComplete() == true

The following code example shows how to make the segment tree incomplete.

Making the segment tree incomplete

IlvSegmentedHyperEdge seghyperedge = ...
seghyperedge.setAutoConnect(false);
// ... this will not add any segments automatically
seghyperedge.addFrom(node);
seghyperedge.addTo(node);
// ... now the segment tree is incomplete, since the new hyperedge ends
//     are not connected ...
// seghyperedge.isSegmentSetComplete() == false

The autoconnect mode is enabled by default.

The API of IlvSegmentedHyperEdge contains further operations that keep the segment tree complete.

Methods of IlvSegmentedHyperEdge for keeping the segment tree complete

Method	Description
splitSegment	Variants of this operation exist. They split a segment into a sequence of segments, that is, a bend will occur at the position where the segment was split. See the Java™ API reference manual for information about the variants.
joinSegments	This is the inverse of the split operation. It joins two segments, so that instead of two, only one segment is used. This operation removes a bend in the shape of the hyperedge.
setSegmentAngle	Changes the angle of the input segment. If the input segment is connected, this will work only if no incident segment is colinear with the new angle.
setEndSegmentAngle	Changes the angle of the segment that is incident to the input hyperedge end. It reorganizes the segment tree so that the desired angle is possible for the segment at the input end.

See IlvSegmentedHyperEdge for more information on segmented hyperedges.