[vtkusers] Bug (?? + solution) in vtkPolyData::GetCell(int cellId, vtkGeneri cCell *cell)

[Schaap, J.A. (LKEB)]

Hi,

I'm not sure if this is a bug, or if my filter generates corrupt polydata
output...
But, I think the following piece of code is not correct. (Copied from
vtkPolyData.cxx dated 2-2-2001)

//-------------------------
//Begin Code snippet
//-------------------------

void vtkPolyData::GetCell(int cellId, vtkGenericCell *cell)
{
  int             i, loc, numPts, *pts;
  unsigned char   type;
  float           x[3];

  if ( !this->Cells )
    {
    this->BuildCells();
    }

  type = this->Cells->GetCellType(cellId);
  loc = this->Cells->GetCellLocation(cellId);

  switch (type)
    {
    case VTK_VERTEX:
      cell->SetCellTypeToVertex();
      this->Verts->GetCell(loc,numPts,pts);
      break;

    case VTK_POLY_VERTEX:
      cell->SetCellTypeToPolyVertex();
      this->Verts->GetCell(loc,numPts,pts);
      cell->PointIds->SetNumberOfIds(numPts); //reset number of points
      cell->Points->SetNumberOfPoints(numPts);
      break;

    case VTK_LINE: 
      cell->SetCellTypeToLine();
      this->Lines->GetCell(loc,numPts,pts);
      break;

    case VTK_POLY_LINE:
      cell->SetCellTypeToPolyLine();
      this->Lines->GetCell(loc,numPts,pts);
      cell->PointIds->SetNumberOfIds(numPts); //reset number of points
      cell->Points->SetNumberOfPoints(numPts);
      break;

    case VTK_TRIANGLE:
      cell->SetCellTypeToTriangle();
      this->Polys->GetCell(loc,numPts,pts);
      break;

    case VTK_QUAD:
      cell->SetCellTypeToQuad();
      this->Polys->GetCell(loc,numPts,pts);
      break;

    case VTK_POLYGON:
      cell->SetCellTypeToPolygon();
      this->Polys->GetCell(loc,numPts,pts);
      cell->PointIds->SetNumberOfIds(numPts); //reset number of points
      cell->Points->SetNumberOfPoints(numPts);
      break;

    case VTK_TRIANGLE_STRIP:
      cell->SetCellTypeToTriangleStrip();
      this->Strips->GetCell(loc,numPts,pts);
      cell->PointIds->SetNumberOfIds(numPts); //reset number of points
      cell->Points->SetNumberOfPoints(numPts);
      break;

    default:
      cell->SetCellTypeToEmptyCell();
    }

  for (i=0; i < numPts; i++)
    {
    cell->PointIds->SetId(i,pts[i]);
    this->Points->GetPoint(pts[i], x);
    cell->Points->SetPoint(i, x);
    }
}

//-------------------------
//End Code snippet
//-------------------------


If the variable cell is set to EmptyCell (in the default case in the switch)
then it crashes in the following for-loop. 

The solution is to either test is the cell is an EmptyCell before the for
loop, or to set numPts = 0 in the default case.

Best Regards, Jorrit.

--
Jorrit Schaap
Division of Image Processing
Leiden University Medical Center
+31 71 5266206