Doxygen/html/Examples_2DataRepresentation_2Mesh_2MeshCellVisitor_8cxx-example.html

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//  Software Guide : BeginLatex

//

//  In order to facilitate access to particular cell types, a convenience

//  mechanism has been built-in on the \doxygen{Mesh}. This mechanism is

//  based on the \emph{Visitor Pattern} presented  in \cite{Gamma1995}. The

//  visitor pattern is designed to facilitate the process of walking through

//  an heterogeneous list of objects sharing a common base class.

//

//  The first requirement for using the \code{CellVisitor} mechanism it to

//  include the \code{CellInterfaceVisitor} header file.

//

//  \index{itk::Mesh!CellVisitor}

//  \index{itk::Mesh!CellInterfaceVisitor}

//  \index{CellVisitor}

//  \index{CellInterfaceVisitor}

//

//  Software Guide : EndLatex


#include "itkMesh.h"

#include "itkLineCell.h"

#include "itkTetrahedronCell.h"


// Software Guide : BeginCodeSnippet

#include "itkCellInterfaceVisitor.h"

// Software Guide : EndCodeSnippet


//  Software Guide : BeginLatex

//

//  The typical mesh types are now declared.

//

//  Software Guide : EndLatex


// Software Guide : BeginCodeSnippet

using PixelType = float;

using MeshType = itk::Mesh<PixelType, 3>;


using CellType = MeshType::CellType;


using VertexType = itk::VertexCell<CellType>;

using LineType = itk::LineCell<CellType>;

using TriangleType = itk::TriangleCell<CellType>;

using TetrahedronType = itk::TetrahedronCell<CellType>;

// Software Guide : EndCodeSnippet


//  Software Guide : BeginLatex

//

//  Then, a custom CellVisitor class should be declared. In this particular

//  example, the visitor class is intended to act only on \code{TriangleType}

//  cells. The only requirement on the declaration of the visitor class is

//  that it must provide a method named \code{Visit()}. This method expects as

//  arguments a cell identifier and a pointer to the \emph{specific} cell type

//  for which this visitor is intended. Nothing prevents a visitor class from

//  providing \code{Visit()} methods for several different cell types.  The

//  multiple methods will be differentiated by the natural C++ mechanism of

//  function overload. The following code illustrates a minimal cell visitor

//  class.

//

//  \index{itk::Mesh!CellInterfaceVisitor}

//  \index{CellInterfaceVisitor!requirements}

//  \index{CellInterfaceVisitor!Visit()}

//

//  Software Guide : EndLatex


#ifndef CustomTriangleVisitorDefine

#  define CustomTriangleVisitorDefine

// Software Guide : BeginCodeSnippet

class CustomTriangleVisitor

{

public:

  using TriangleType = itk::TriangleCell<CellType>;

  void

  Visit(unsigned long cellId, TriangleType * t)

  {

    std::cout << "Cell # " << cellId << " is a TriangleType ";

    std::cout << t->GetNumberOfPoints() << std::endl;

  }

  CustomTriangleVisitor() = default;

  virtual ~CustomTriangleVisitor() = default;

};

// Software Guide : EndCodeSnippet

#endif // CustomTriangleVisitorDefine


int

main(int, char *[])

{

  auto mesh = MeshType::New();


  // Creating the points and inserting them in the mesh

  //

  MeshType::PointType point0;

  MeshType::PointType point1;

  MeshType::PointType point2;

  MeshType::PointType point3;


  point0[0] = -1;

  point0[1] = -1;

  point0[2] = -1;

  point1[0] = 1;

  point1[1] = 1;

  point1[2] = -1;

  point2[0] = 1;

  point2[1] = -1;

  point2[2] = 1;

  point3[0] = -1;

  point3[1] = 1;

  point3[2] = 1;


  mesh->SetPoint(0, point0);

  mesh->SetPoint(1, point1);

  mesh->SetPoint(2, point2);

  mesh->SetPoint(3, point3);


  // Creating and associating the Tetrahedron

  //

  CellType::CellAutoPointer cellpointer;


  cellpointer.TakeOwnership(new TetrahedronType);

  cellpointer->SetPointId(0, 0);

  cellpointer->SetPointId(1, 1);

  cellpointer->SetPointId(2, 2);

  cellpointer->SetPointId(3, 3);

  mesh->SetCell(0, cellpointer);


  // Creating and associating the Triangles

  //

  cellpointer.TakeOwnership(new TriangleType);

  cellpointer->SetPointId(0, 0);

  cellpointer->SetPointId(1, 1);

  cellpointer->SetPointId(2, 2);

  mesh->SetCell(1, cellpointer);


  cellpointer.TakeOwnership(new TriangleType);

  cellpointer->SetPointId(0, 0);

  cellpointer->SetPointId(1, 2);

  cellpointer->SetPointId(2, 3);

  mesh->SetCell(2, cellpointer);


  cellpointer.TakeOwnership(new TriangleType);

  cellpointer->SetPointId(0, 0);

  cellpointer->SetPointId(1, 3);

  cellpointer->SetPointId(2, 1);

  mesh->SetCell(3, cellpointer);


  cellpointer.TakeOwnership(new TriangleType);

  cellpointer->SetPointId(0, 3);

  cellpointer->SetPointId(1, 2);

  cellpointer->SetPointId(2, 1);

  mesh->SetCell(4, cellpointer);


  // Creating and associating the Edges

  //

  cellpointer.TakeOwnership(new LineType);

  cellpointer->SetPointId(0, 0);

  cellpointer->SetPointId(1, 1);

  mesh->SetCell(5, cellpointer);


  cellpointer.TakeOwnership(new LineType);

  cellpointer->SetPointId(0, 1);

  cellpointer->SetPointId(1, 2);

  mesh->SetCell(6, cellpointer);


  cellpointer.TakeOwnership(new LineType);

  cellpointer->SetPointId(0, 2);

  cellpointer->SetPointId(1, 0);

  mesh->SetCell(7, cellpointer);


  cellpointer.TakeOwnership(new LineType);

  cellpointer->SetPointId(0, 1);

  cellpointer->SetPointId(1, 3);

  mesh->SetCell(8, cellpointer);


  cellpointer.TakeOwnership(new LineType);

  cellpointer->SetPointId(0, 3);

  cellpointer->SetPointId(1, 2);

  mesh->SetCell(9, cellpointer);


  cellpointer.TakeOwnership(new LineType);

  cellpointer->SetPointId(0, 3);

  cellpointer->SetPointId(1, 0);

  mesh->SetCell(10, cellpointer);


  // Creating and associating the Vertices

  //

  cellpointer.TakeOwnership(new VertexType);

  cellpointer->SetPointId(0, 0);

  mesh->SetCell(11, cellpointer);


  cellpointer.TakeOwnership(new VertexType);

  cellpointer->SetPointId(0, 1);

  mesh->SetCell(12, cellpointer);


  cellpointer.TakeOwnership(new VertexType);

  cellpointer->SetPointId(0, 2);

  mesh->SetCell(13, cellpointer);


  cellpointer.TakeOwnership(new VertexType);

  cellpointer->SetPointId(0, 3);

  mesh->SetCell(14, cellpointer);


  // Simple verification of the number of points and cells inserted

  //

  std::cout << "# Points= " << mesh->GetNumberOfPoints() << std::endl;

  std::cout << "# Cell  = " << mesh->GetNumberOfCells() << std::endl;


  //  Software Guide : BeginLatex

  //

  // \index{itk::Mesh!Cell\-Interface\-Visitor\-Implementation}

  // \index{itk::Mesh!CellInterfaceVisitor}

  // \index{itk::Mesh!CellVisitor}

  // \index{CellVisitor}

  //

  //  This newly defined class will now be used to instantiate a cell visitor.

  //  In this particular example we create a class

  //  \code{CustomTriangleVisitor} which will be invoked each time a triangle

  //  cell is found while the mesh iterates over the cells.

  //

  //  Software Guide : EndLatex


  // Software Guide : BeginCodeSnippet

  using TriangleVisitorInterfaceType =

    itk::CellInterfaceVisitorImplementation<PixelType,

                                            MeshType::CellTraits,

                                            TriangleType,

                                            CustomTriangleVisitor>;

  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex

  //

  //  Note that the actual \code{CellInterfaceVisitorImplementation} is

  //  templated over the PixelType, the CellTraits, the CellType to be visited

  //  and the Visitor class that defines with will be done with the cell.

  //

  //  A visitor implementation class can now be created using the normal

  //  invocation to its \code{New()} method and assigning the result to a

  //  \doxygen{SmartPointer}.

  //

  //  Software Guide : EndLatex


  // Software Guide : BeginCodeSnippet

  auto triangleVisitor = TriangleVisitorInterfaceType::New();

  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex

  //

  //  Many different visitors can be configured in this way. The set of all

  //  visitors can be registered with the MultiVisitor class provided for the

  //  mesh. An instance of the MultiVisitor class will walk through the cells

  //  and delegate action to every registered visitor when the appropriate

  //  cell type is encountered.

  //

  //  Software Guide : EndLatex


  // Software Guide : BeginCodeSnippet

  using CellMultiVisitorType = CellType::MultiVisitor;

  auto multiVisitor = CellMultiVisitorType::New();

  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex

  //

  //  The visitor is registered with the Mesh using the \code{AddVisitor()}

  //  method.

  //

  //  \index{itk::Mesh!AddVisitor()}

  //

  //  Software Guide : EndLatex


  // Software Guide : BeginCodeSnippet

  multiVisitor->AddVisitor(triangleVisitor);

  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex

  //

  //  Finally, the iteration over the cells is triggered by calling the method

  //  \code{Accept()} on the \code{itk::Mesh}.

  //

  //  \index{itk::Mesh!Accept()}

  //

  //  Software Guide : EndLatex


  // Software Guide : BeginCodeSnippet

  mesh->Accept(multiVisitor);

  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex

  //

  //  The \code{Accept()} method will iterate over all the cells and for each

  //  one will invite the MultiVisitor to attempt an action on the cell. If no

  //  visitor is interested on the current cell type the cell is just ignored

  //  and skipped.

  //

  //  MultiVisitors make it possible to add behavior to the cells without

  //  having to create new methods on the cell types or creating a complex

  //  visitor class that knows about every CellType.

  //

  //  Software Guide : EndLatex


  return EXIT_SUCCESS;

}