Some layout algorithms use random numbers (or randomly chosen parameters) for which they accept a user-defined seed value. For example, the Random Layout uses the random generator to compute the coordinates of the nodes.

Subclasses of IlvGraphLayout that are designed to support this mechanism allow the user to choose one of three ways of initializing the random generator:

The user chooses the initialization option depending on what happens when the layout algorithm is performed again on the same graph. If the same seed value is used, the same layout is produced, which may be the desired result. In other situations, the user may want to produce different layouts in order to select the best one. This can be achieved by performing the layout several times using different seed values.

Here is an example of how this parameter can be used in combination with the IlvRandomLayout class in your implementation of the method IlvGraphLayout::layout():

To specify the seed value, use the method:

and to obtain the current value:

The default value is 0.

You can read the current option using the method:

To indicate whether a subclass of IlvGraphLayout supports this parameter, the following method is provided:

The default implementation returns IlFalse. A subclass can override this method in order to return IlTrue to indicate that this parameter is supported.