Graph Management

Graphic objects representing graphs are stored in instances of the IlvGrapher class. This class derives from the IlvManager class and inherits all its features. The constructors of IlvManager (the base class) and IlvGrapher have the same parameters:


IlvGrapher(IlvDisplay* display, int layers = 2, IlBoolean useacc = IlTrue, IlvUShort maxInList = IlvMaxObjectsInList, IlvUShort maxInNode = IlvMaxObjectsInList);

In addition to the IlvManager concepts, the IlvGrapher class introduces a distinction between three types of graphic objects:

Nodes - Nodes are the visual reference points in a hierarchy of information. A node is a graphic object—a subtype of the IlvGraphic class—that takes on a particular functionality when added to the grapher with the addNode method. This functionality allows links and nodes to stay connected when a node is moved.

Links - Links are the visual representation of connections between nodes. A link is an instance of the IlvLinkImage class or one of its subclasses. It is added to the grapher with the IlvGrapher::addLink method. Since links can only exist between two existing nodes, you must create them with two graphic objects that are known as nodes by the grapher. You can use ghost nodes (added with the IlvGrapher::addGhostNode method) to create free-end links.

Ordinary graphic objects - As is the case in a regular IlvManager instance, you can incorporate in your graph any IlvGraphic objects that represent neither nodes nor links.

The IlvGrapher class provides a set of member functions to manage links and nodes. You can, for example, replace a link with another one through a call to the changeLink method.

You can also transform a graphic object stored in the grapher into a node by calling the makeNode method. You can apply this method to a grapher link. This allows you to connect the link to other nodes. When dealing with a link that has a node behavior, you must make sure that there is no cycle in the geometric dependencies that govern the position of this link. Similarly, you can transform a graphic object into a grapher link with the makeLink method. The created link will be an instance of the IlvLinkHandle class, which is described in section Grapher Links.

Once objects are stored in an IlvGrapher, you can make a distinction between nodes, links, and ordinary graphic instances by using the isNode and isLink methods.

The IlvGrapher API also provides several methods to query the topology of your graph. For example, you can test whether two given nodes are connected by using the isLinkBetween method. You can also retrieve all the outgoing or incoming links of a node by using the getLinks method.

The sample code below shows how to use the IlvGrapher::mapLinks method to select all the outgoing links of a node:

Finally, the IlvGrapher class provides two predefined layout methods to arrange nodes in a vertical or horizontal tree structure. These layouts are implemented in the nodeXPretty and nodeYPretty methods.

An example showing how to create a simple grapher is provided in the <ILVHOME>/samples/grapher/simple directory. Also, you can refer to the Rogue Wave Views Grapher Reference Manual for more information on the member functions of the IlvGrapher class.

The IlvGrapher class reads graphs by using the IlvGraphInputFile class, and saves graphs by using the IlvGraphOutputFile class.

The IlvGraphOutputFile class is a subclass of IlvManagerOutputFile. In this subclass, the virtual method IlvGraphOutputFile::writeObject has been redefined to add specific information about each object before its description block. In our case, this information is the layer index, the type of the object (node, link, both, or an ordinary object), as well as the connection pins. Connection pins are described in section Grapher Links.

The IlvGraphInputFile class is a subclass of IlvManagerInputFile. In this subclass the virtual method IlvGraphInputFile::readObject has been redefined to read the specific information written by the IlvGraphOutputFile::writeObject method.