// SPDX-FileCopyrightText: Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
// SPDX-FileCopyrightText: Copyright 2008 Sandia Corporation
// SPDX-License-Identifier: LicenseRef-BSD-3-Clause-Sandia-USGov
/**
 * @class   vtkSpanTreeLayoutStrategy
 *
 * vtkSpanTreeLayout is a strategy for drawing directed graphs that
 * works by first extracting a spanning tree (more accurately, a
 * spanning forest), and using this both to position graph vertices
 * and to plan the placement of non-tree edges.  The latter are drawn
 * with the aid of edge points to produce a tidy drawing.
 *
 * The approach is best suited to "quasi-trees", graphs where the number
 * of edges is of the same order as the number of nodes; it is less well
 * suited to denser graphs.  The boolean flag DepthFirstSpanningTree
 * determines whether a depth-first or breadth-first strategy is used to
 * construct the underlying forest, and the choice of strategy affects
 * the output layout significantly.  Informal experiments suggest that
 * the breadth-first strategy is better for denser graphs.
 *
 * Different layouts could also be produced by plugging in alternative
 * tree layout strategies.  To work with the method of routing non-tree
 * edges, any strategy should draw a tree so that levels are equally
 * spaced along the z-axis, precluding for example the use of a radial
 * or balloon layout.
 *
 * vtkSpanTreeLayout is based on an approach to 3D graph layout first
 * developed as part of the "tulip" tool by Dr. David Auber at LaBRI,
 * U.Bordeaux: see www.tulip-software.org
 *
 * This implementation departs from the original version in that:
 * (a) it is reconstructed to use Titan/VTK data structures;
 * (b) it uses a faster method for dealing with non-tree edges,
 *     requiring at most two edge points per edge
 * (c) allows for plugging in different tree layout methods
 * (d) allows selection of two different strategies for building
 *     the underlying layout tree, which can yield significantly
 *     different results depending on the data.
 *
 * @par Thanks:
 * Thanks to David Duke from the University of Leeds for providing this
 * implementation.
 */

#ifndef vtkSpanTreeLayoutStrategy_h
#define vtkSpanTreeLayoutStrategy_h

#include "vtkGraphLayoutStrategy.h"
#include "vtkInfovisLayoutModule.h" // For export macro

VTK_ABI_NAMESPACE_BEGIN
class VTKINFOVISLAYOUT_EXPORT vtkSpanTreeLayoutStrategy : public vtkGraphLayoutStrategy
{
public:
  static vtkSpanTreeLayoutStrategy* New();

  vtkTypeMacro(vtkSpanTreeLayoutStrategy, vtkGraphLayoutStrategy);
  void PrintSelf(ostream& os, vtkIndent indent) override;

  ///@{
  /**
   * If set, base the layout on a depth-first spanning tree,
   * rather than the default breadth-first spanning tree.
   * Switching between DFT and BFT may significantly change
   * the layout, and choice must be made on a per-graph basis.
   * Default value is off.
   */
  vtkSetMacro(DepthFirstSpanningTree, bool);
  vtkGetMacro(DepthFirstSpanningTree, bool);
  vtkBooleanMacro(DepthFirstSpanningTree, bool);
  ///@}

  /**
   * Perform the layout.
   */
  void Layout() override;

protected:
  vtkSpanTreeLayoutStrategy();
  ~vtkSpanTreeLayoutStrategy() override;

  vtkGraphLayoutStrategy* TreeLayout;
  bool DepthFirstSpanningTree;

private:
  vtkSpanTreeLayoutStrategy(const vtkSpanTreeLayoutStrategy&) = delete;
  void operator=(const vtkSpanTreeLayoutStrategy&) = delete;
};

VTK_ABI_NAMESPACE_END
#endif
