[vtkusers] vtkCellArray - efficient use

[Paul Harris]

Thanks Burlen,

Another question, I checked the code for CSCS's vtkPointSpriteMapper and it
will work just fine if I put all the verticies into one cell...

Is there any reason why I should put one vertex per cell ?  EG, I imagine it
may be required when adding support for point-picking ?

thanks,
Paul


2009/1/17 Burlen Loring <burlen.loring at kitware.com>

> Here is an example using vertex cells.
>
>
>  vtkIdTypeArray *va=vtkIdTypeArray::New();
>  va->SetNumberOfTuples(2*nCells);
>  vtkIdType *verts=va->GetPointer(0);
>  vtkPoints *pts=vtkPoints::New();
>  pts->SetData(xyzArray);
>  for (int i=0; i<nCells; ++i)
>   {
>   verts[0]=1;
>   verts[1]=i;
>   verts+=2;
>   }
>  polydataset->SetPoints(pts);
>  pts->Delete();
>  vtkCellArray *cells=vtkCellArray::New();
>  cells->SetCells(static_cast<vtkIdType>(nCells),va);
>  polydataset->SetVerts(cells);
>  cells->Delete();
>  va->Delete();
>
>
> Paul Harris wrote:
>
>> Hi,
>>
>> I have the following code:
>>
>> vtkCellArray * p_cells = vtkCellArray::New();
>>
>> p_cells->Allocate( ids.size() );
>>
>> for ( vector<vtkIdType>::const_iterator id = ids.begin(), id_end =
>> ids.end(); id != id_end; ++id )
>>   p_cells->InsertNextCell(1,&*c);
>>
>>
>> But, I am not sure that my Allocate() call is correct.  Should it be:
>> Allocate(ids.size()*2);
>>
>> ... the reason I ask is that I wanted to try and use
>> p_cells->WritePointer() to do the copying with a memcpy, but it looks like
>> the format of a CellArray is something like:
>>
>> [cellid, pointid, cellid, pointid, cellid, pointid]
>>
>> if i had 2 points per cell it would be
>> [cellid, point1, point2, cellid, point1, point2, etc]
>>
>> if this is so, then in order to create a cellarray of 20 points, each in
>> their own cells, i'd need to alloc room for 40.
>>
>>
>> Am I reading the code correctly?
>> Does anyone do efficient copies, or does everyone use InsertNextEtc()
>> methods?
>>
>> thanks,
>> Paul
>>
>>
>>
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