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LayerSweepCrossingMinimizer
is still the main class and implements the layer-sweep approach to crossing minimization. However, it does not know anymore how to do the actual crossing minimization step for a given pair of layers. However, it implements the cross counting algorithms, since these are not affected by the actual crossing minimization algorithm used.- The
CompoundGraphLayerCrossingMinimizer
is used to implement the actual crossing minimization step for a given pair of layers. For flat graphs, it just takes the set of nodes in the layer and uses anICrossingMinimizationHeuristic
to compute their order. For compound graphs, it works its way from the nodes contained in the innermost compound node up to the outermost compound node, computing an order for each and treating them as an atomic set of nodes afterwards. - An
ICrossingMinimizationHeuristic
is used to determine the ordering of a given set of nodes. The result is expected to adhere to any constraints, such as node successor constraints and layout unit constraints. The usual heuristic would be theBarycenterHeuristic
. - The
IPortDistributor
is used by theLayerSweepCrossingMinimizer
to calculate port ranks needed to determine node barycenters, and to handle the final port distribution. The standard implementation is theNodeRelativePortDistributor
. We're planning to add aSimplePortDistributer
as well that calculates port ranks as KLoDD did back in the day. - If a heuristic doesn't know how to handle constraints, it can make use of an
IConstraintResolver
to resolve any constraints after it has determined an initial node ordering. The standard implementation is theForsterConstraintResolver
, which implements a constraint resolving heuristic proposed by Michael Forster. NodeGroup
s are used by theCompoundGraphLayerCrossingMinimizer
to encapsulate sets of nodes contained in a single compound node, to treat them as an atomic group with fixed ordering.
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