Method ComputeCellsBounds

Common/DataModel/vtkPolyData.cxx:305–406

------------------------------------------------------------------------------ This method only considers points that are used by one or more cells. Thus unused points make no contribution to the bounding box computation. This is more costly to compute than using just the points, but for rendering and historical reasons, produces preferred results.

// is more costly to compute than using just the points, but for rendering
// and historical reasons, produces preferred results.
void vtkPolyData::ComputeCellsBounds()
{
  if (this->GetMeshMTime() > this->CellsBoundsTime)
  {
    // If there are no cells, uninitialize the bounds.
    const vtkIdType numPts = this->GetNumberOfPoints();
    const vtkIdType numPDCells = this->GetNumberOfCells();
    if (numPDCells <= 0)
    {
      vtkMath::UninitializeBounds(this->CellsBounds);
      return;
    }

    // We are going to compute the bounds
    this->CellsBoundsTime.Modified();

    // Make sure this vtkPolyData has points.
    if (this->Points == nullptr || numPts <= 0 || numPDCells <= 0)
    {
      vtkMath::UninitializeBounds(this->CellsBounds);
      return;
    }

    // With cells available, loop over the cells of the polydata.
    // Mark points that are used by one or more cells. Unmarked
    // points do not contribute.
    vtkCellArray* cellArrays[4] = { this->GetVerts(), this->GetLines(), this->GetPolys(),
      this->GetStrips() };

    // Process each cell array separately. Note that threading is only used
    // if the model is big enough (since there is a cost to spinning up the
    // thread pool).

    // Create uses array initialized to 0
    vtkSMPThreadLocalObject<vtkIdList> tlCellPointIds;
    if (numPDCells > vtkSMPTools::THRESHOLD)
    {
      // Create uses array initialized to 0 and supporting threaded access
      std::atomic<unsigned char>* ptUses = new std::atomic<unsigned char>[numPts]();
      for (const auto& cellArray : cellArrays)
      {
        const auto numCells = cellArray->GetNumberOfCells();
        if (numCells <= 0)
        {
          continue;
        }
        // Lambda to threaded mark used points
        vtkSMPTools::For(0, numCells,
          [&](vtkIdType beginCellId, vtkIdType endCellId)
          {
            auto cellPointIds = tlCellPointIds.Local();
            vtkIdType npts, ptIdx;
            const vtkIdType* pts;
            for (vtkIdType cellId = beginCellId; cellId < endCellId; ++cellId)
            {
              cellArray->GetCellAtId(cellId, npts, pts, cellPointIds);
              for (ptIdx = 0; ptIdx < npts; ++ptIdx)
              {