Method Orient

Filters/General/vtkIntersectionPolyDataFilter.cxx:1753–1800

//------------------------------------------------------------------------------

void vtkIntersectionPolyDataFilter::Impl ::Orient(
  vtkPolyData* pd, vtkTransform* transform, vtkPolyData* boundary, vtkPolygon* boundarypoly)
{
  // Orient this loop in a counter clockwise direction in preparation for
  // cell splitting. For delaunay2d, the polygon should be in CCW order, but
  // also for ear clipping method, it is nice to have also in CCW order.
  vtkSmartPointer<vtkTransformPolyDataFilter> transformer =
    vtkSmartPointer<vtkTransformPolyDataFilter>::New();
  vtkSmartPointer<vtkPolyData> transformedpd = vtkSmartPointer<vtkPolyData>::New();

  transformer->SetInputData(pd);
  transformer->SetTransform(transform);
  transformer->Update();
  transformedpd = transformer->GetOutput();

  double area = 0;
  double tedgept1[3];
  double tedgept2[3];
  vtkIdType nextPt;
  for (nextPt = 0; nextPt < pd->GetNumberOfPoints() - 1; nextPt++)
  {
    transformedpd->GetPoint(nextPt, tedgept1);
    transformedpd->GetPoint(nextPt + 1, tedgept2);
    area = area + (tedgept1[0] * tedgept2[1]) - (tedgept2[0] * tedgept1[1]);
  }
  transformedpd->GetPoint(nextPt, tedgept1);
  transformedpd->GetPoint(0, tedgept2);
  area = area + (tedgept1[0] * tedgept2[1]) - (tedgept2[0] * tedgept1[1]);

  if (area < 0)
  {
    for (nextPt = pd->GetNumberOfPoints() - 1; nextPt > -1; nextPt--)
    {
      boundarypoly->GetPointIds()->InsertNextId(nextPt);
    }
  }
  else
  {
    for (nextPt = 0; nextPt < pd->GetNumberOfPoints(); nextPt++)
    {
      boundarypoly->GetPointIds()->InsertNextId(nextPt);
    }
  }
  vtkSmartPointer<vtkCellArray> cellarray = vtkSmartPointer<vtkCellArray>::New();
  cellarray->InsertNextCell(boundarypoly);
  boundary->SetPoints(pd->GetPoints());
  boundary->SetPolys(cellarray);
}

//------------------------------------------------------------------------------