[vtk-developers] potential speedup for the vtkpolydatatoimagestencil

[David Gobbi]

Out of curiosity, how much of a performance difference does it make?

 - David

On Wed, Feb 29, 2012 at 3:04 PM, Mark Roden <mmroden at gmail.com> wrote:
> OK, I got it to work.
>
> For people who are following this thread, converting rtstructs from
> vtkgdcmpolydata reader into a binary image but wanting to avoid
> extrusion, this code will convert the data from polys to lines:
>
>
> //just want lines returned, nothing else, for fast stenciling.
> vtkPolyData* ConvertToLines(vtkPolyData * const data) {
>    vtkPolyData* returnedData = vtkPolyData::New();
>    returnedData->DeepCopy(data);
>
>    vtkPoints* newPoints = vtkPoints::New();
>
>    int theNumPoints = returnedData->GetNumberOfPoints();
>
>    if (theNumPoints == 1){
>        double* pt = data->GetPoint(0);
>        newPoints->InsertNextPoint(pt);
>        returnedData->SetPoints(newPoints);
>    } else {
>
>        int i;
>        //borrowed this code from the polydatatostencil code
>        //we know that each polygon is coplanar, so do that here.
>        //also, closes the polygon, but should check to see if that's necessary.
>        vtkMergePoints* theMerge = vtkMergePoints::New();
>        double bounds[6];
>        data->GetBounds(bounds);
>        theMerge->InitPointInsertion(newPoints, bounds);
>        vtkCellArray* polys = (data->GetPolys());
>        vtkCellArray* lines = vtkCellArray::New();
>        returnedData->SetLines(lines);//blank them out, just in case
>        //each cell in the poly array is a polyline, I contend.
>        int theNumPolys = polys->GetNumberOfCells();
>        lines->Allocate(theNumPolys);
>        polys->InitTraversal();
>        vtkPoints* oldPoints = data->GetPoints();
>        for (int j = 0; j < theNumPolys; j++){
>            vtkIdType numPoints;
>            vtkIdType* ptIds;
>            polys->GetNextCell(numPoints, ptIds);
>            lines->InsertNextCell(numPoints+1);//close the end of the poly
>            int zeroPtId = 0;
>            double zeroPt[3];
>            for (i = 0; i < numPoints; i++){
>              vtkIdType ptId;
>              double point[3];
>              oldPoints->GetPoint(ptIds[i], point);
>              theMerge->InsertUniquePoint(point, ptId);
>              lines->InsertCellPoint(ptId);
>              newPoints->InsertNextPoint(point);
>              if (i == 0){
>                zeroPtId = ptId;
>                zeroPt[0] = point[0];
>                zeroPt[1] = point[1];
>                zeroPt[2] = point[2];
>              }
>            }
>            newPoints->InsertNextPoint(zeroPt);
>            theMerge->InsertUniquePoint(zeroPt, zeroPtId);
>            lines->InsertCellPoint(zeroPtId);//start from the beginning
>        }
>        returnedData->SetPoints(newPoints);
>        returnedData->SetLines(lines);
>        vtkCellArray* blank = vtkCellArray::New();
>        returnedData->SetPolys(blank);
>        blank->Delete();
>        lines->Delete();
>    }
>    newPoints->Delete();
>
>    return returnedData;
> }