y.layout.router.polyline
Class PathSearch

java.lang.Object
  y.layout.router.polyline.PathSearch

public class PathSearch
extends Object

A pathfinding algorithm that calculates the shortest (that means the cheapest) paths for a set of edges through a GraphPartition.

It is based on an A*-algorithm and uses PartitionCells as steps between source node and target node.
In each step, the algorithm takes a CellEntrance, that consists mainly of a PartitionCell and from where it was entered, from a queue with all seen CellEntrances, determines all possible neighbor cells and their enter intervals and enqueues the resulting CellEntrances.
To influence the order in which the CellEntrances will be processed, the path search assigns real costs (like Dijkstra) as well as heuristic costs (A*-algorithm's heuristic) to the enqueued CellEntrances. The real costs arise from entering a neighbor cell, e.g. a bend has to be created, while the heuristic costs are an estimation of how expensive it will be to reach the target node continuing the path with this neighbor cell. Therefor, the path search prefers searching in the direction where the target node lies. The CellEntrance with the lowest combined costs is processed next until a target cell is reached.

PathSearchExtensions modify the path search as they are able to add start entrances and weigh them with costs. They also add real and heuristic costs to CellEntrances that are created for the currently entered PartitionCell and calculate shorter enter intervals that are less expensive to pass.

The algorithm gets a PathSearchContext which provides information about the graph and the currently routed edge. It also stores the results of the path search that can be retrieved calling PathSearchContext.getPathSearchResult().

See Also:

addPathSearchExtension(PathSearchExtension), addAdditionalEnterIntervalCalculator(EnterIntervalCalculator)

Constructor Summary

PathSearch()
Creates a new instance

Method Summary

boolean	addAdditionalEnterIntervalCalculator(EnterIntervalCalculator enterIntervalCalculator) Adds a new interval calculator to the list of registered interval calculators.
boolean	addPathSearchExtension(PathSearchExtension extension) Adds the given extension to the list of path search extensions.
protected double[]	calculateCosts(CellEntrance currentEntrance, PartitionCell enteredCell, OrthogonalInterval[] enterIntervals, EdgeCellInfo[] lastEdgeCellInfos, PathSearchContext context, double[] maxAllowedCosts) Returns the costs for getting from the current CellEntrance to the neighboring PartitionCell using different enter intervals.
protected double	calculateHeuristicCosts(CellEntrance entrance, PathSearchContext context) Returns estimated costs for the rest of the path when using the given CellEntrance for the next step in path search.
void	clear() Resets all registered path search extensions and DataProviders added by PathSearch.
protected void	decreasePenaltySettings(PenaltySettings penaltySettings, double decreaseFactor, PathSearchContext context) Decreases the given penalty settings for the current edge.
protected void	finalizePath(Path path) Informs all registered path search extensions about completing a path by calling their finalizePath(Path) method.
void	findPaths(PathSearchContext context) Finds paths for the edges in the given context and stores them in its PathSearchResult.
protected void	findPathsForCurrentEdge(PathSearchContext context) Finds the path for the current edge in the given context.
Path	getFinalizedPath(Edge edge) Returns the path for the given edge, if it has been finalized already.
protected void	handleNeighbor(CellEntrance currentEntrance, PartitionCell neighborCell, PathSearchContext context) Adds CellEntrances for every interval through which the neighbor cell can be entered from the current entrance to the queue.
void	init(PathSearchConfiguration configuration) Initializes the path search.
boolean	removeAdditionalEnterIntervalCalculator(EnterIntervalCalculator enterIntervalCalculator) Removes the given interval calculator from the list of registered interval calculators.
boolean	removePathSearchExtension(PathSearchExtension extension) Removes the given extension from the list of path search extensions.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

PathSearch

public PathSearch()

Creates a new instance

Method Detail

addPathSearchExtension

public boolean addPathSearchExtension(PathSearchExtension extension)

Adds the given extension to the list of path search extensions.

Parameters:

extension - The extension to add to this path search.

Returns:

true, if the extension has been added, false otherwise.

removePathSearchExtension

public boolean removePathSearchExtension(PathSearchExtension extension)

Removes the given extension from the list of path search extensions.

Parameters:

extension - The extension to remove from the path search.

Returns:

true, if an extension was removed as a result of this call.

addAdditionalEnterIntervalCalculator

public boolean addAdditionalEnterIntervalCalculator(EnterIntervalCalculator enterIntervalCalculator)

Adds a new interval calculator to the list of registered interval calculators.

Parameters:

enterIntervalCalculator - The calculator to add.

Returns:

true, if the calculator could be added, false otherwise.

removeAdditionalEnterIntervalCalculator

public boolean removeAdditionalEnterIntervalCalculator(EnterIntervalCalculator enterIntervalCalculator)

Removes the given interval calculator from the list of registered interval calculators.

Parameters:

enterIntervalCalculator - The calculator to remove.

Returns:

true, if an interval calculator was removed as a result of this call.

init

public void init(PathSearchConfiguration configuration)

Initializes the path search.

This method also calls PathSearchExtension.initialize(PathSearchConfiguration) for all registered path search extensions.

Parameters:

configuration - The configuration, the path search shall use.

clear

public void clear()

Resets all registered path search extensions and DataProviders added by PathSearch. So, PathSearch is ready to calculate paths for a new layout.

See Also:

PathSearchExtension.cleanup()

getFinalizedPath

public Path getFinalizedPath(Edge edge)

Returns the path for the given edge, if it has been finalized already.

Parameters:

edge - The edge to return the path for.

Returns:

The finalized path for the given edge or null if no path has been found and finalized.

findPathsForCurrentEdge

protected void findPathsForCurrentEdge(PathSearchContext context)

Finds the path for the current edge in the given context. This method:

• calls PathSearchExtension.initializeCurrentEdge(PathSearchContext) for all extensions
• collects and enqueues all start entrances
• iteratively processes the next cheapest cell entrance and
  • adds a Path result after a finalizePath(Path) call if it is a valid target entrance and/or
  • calls handleNeighbor(CellEntrance, PartitionCell, PathSearchContext) for all neighbor cells of the entered cell
• calls PathSearchExtension.finalizeCurrentEdge(PathSearchContext) for all extensions

decreasePenaltySettings

protected void decreasePenaltySettings(PenaltySettings penaltySettings,
                                       double decreaseFactor,
                                       PathSearchContext context)

Decreases the given penalty settings for the current edge.

If finding a path for the current edge takes too long according to the maximum duration of the edge router, the path search for the current edge is canceled and restarted using decreased penalties. The decreaseFactor indicates, how strong the penalties shall be reduced.

If overriding this method please note that the penalty for creating bends should not be reduced as this results in more possible turns of the edge path and therefore a longer runtime of the path search. Furthermore not all penalties should be decreased equally as these decreases would neutralize each other.

Parameters:

penaltySettings - The penalty settings whose penalties shall be reduced.

decreaseFactor - A factor with values between 0 and 1 that indicates how strong to reduce the penalties. 0 means no reduction while 1 means to strongest reduction.

context - The context of the current path search.

findPaths

public void findPaths(PathSearchContext context)

Finds paths for the edges in the given context and stores them in its PathSearchResult.

It initializes its extensions using PathSearchExtension.initializeEdges(PathSearchContext) and delegates the path search for each edge to findPathsForCurrentEdge(PathSearchContext).

The paths calculations for all edges are finalized by calling the extensions' PathSearchExtension.finalizeEdges(PathSearchContext) method and after that the path search result if filled with the path for each edge.

At last the extensions are asked to finalize the path search result using their PathSearchExtension.finalizePathSearchResult(PathSearchResult) callback.

Parameters:

context - The context to use during the path search.

See Also:

PathSearchContext.getEdges(), PathSearchContext.getPathSearchResult()

finalizePath

protected void finalizePath(Path path)

Informs all registered path search extensions about completing a path by calling their finalizePath(Path) method. That way, extensions can collect data about this path to use it later in path search.

Parameters:

path - The path to finalize.

handleNeighbor

protected void handleNeighbor(CellEntrance currentEntrance,
                              PartitionCell neighborCell,
                              PathSearchContext context)

Adds CellEntrances for every interval through which the neighbor cell can be entered from the current entrance to the queue. The algorithm calls this method in every step for every neighbor of the current cell to collect all next possible entrances for the current path. This path consists of several entrances where each knows the entrance they were entered through.

After calculating all possible enter intervals to the given neighbor cell, each interval gets rated with costs.
If there already is an entrance for the neighbor cell whose interval is the same as one of these intervals, this entrance will be used and re-enqueued, so the path search can still reach it. The current entrance is set as its predecessor within the current path and its enter interval and costs will be updated.
If there is an entrance for the neighbor cell whose interval is intersected by a current interval, new entrances will be created with the new enter intervals and enqueued. The same happens if there is no entrance that matches one of the current intervals, yet. Costs will be added.
If there are some entries afterwards, that are intersected by the current interval and have higher costs, they will be removed from the queue.

Parameters:

currentEntrance - the current cell entrance

neighborCell - the neighbor cell that is handled.

context - context information

See Also:

calculateCosts(CellEntrance, PartitionCell, OrthogonalInterval[], EdgeCellInfo[], PathSearchContext, double[]), calculateHeuristicCosts(CellEntrance, PathSearchContext)

calculateCosts

protected double[] calculateCosts(CellEntrance currentEntrance,
                                  PartitionCell enteredCell,
                                  OrthogonalInterval[] enterIntervals,
                                  EdgeCellInfo[] lastEdgeCellInfos,
                                  PathSearchContext context,
                                  double[] maxAllowedCosts)

Returns the costs for getting from the current CellEntrance to the neighboring PartitionCell using different enter intervals. It is called by handleNeighbor(CellEntrance, PartitionCell, PathSearchContext) to determine the costs for all CellEntrances that it will create and enqueue afterwards.

The costs for the given enter intervals are retrieved from all registered PathSearchExtensions. The calculation stops when it reaches the given maximum cost value.

Parameters:

currentEntrance - the current cell entrance.

enteredCell - the cell to enter.

enterIntervals - the different entering intervals of the entered cell.

lastEdgeCellInfos - information about how the last cell was crossed.

context - context information.

maxAllowedCosts - the maximum costs an enter interval may induce. If this cost is exceeded, no further additional costs for this interval are calculated.

Returns:

the costs for getting from the current cell to the entered cell using the different enter intervals.

See Also:

PathSearchExtension.calculateCosts(CellEntrance, PartitionCell, OrthogonalInterval, EdgeCellInfo, double)

calculateHeuristicCosts

protected double calculateHeuristicCosts(CellEntrance entrance,
                                         PathSearchContext context)

Returns estimated costs for the rest of the path when using the given CellEntrance for the next step in path search. It is called by handleNeighbor(CellEntrance, PartitionCell, PathSearchContext) to determine the heuristic part of the costs the entrance will be enqueued with.

The heuristic costs for the given entrance are retrieved from all registered PathSearchExtensions.

Parameters:

entrance - The current entrance.

context - Context information.

Returns:

the heuristic costs for the rest of the past if using the given entrance.

See Also:

PathSearchExtension.calculateHeuristicCosts(CellEntrance)