[vtk-developers] VTK 4 compatibility removal - update

[Berk Geveci]

Hi folks,

I wanted to give you an update on where I am in removing the VTK 4
compatibility layer and the issues I have encountered. For reference,
see:

http://www.vtk.org/Wiki/VTK/Remove_VTK_4_Compatibility

Specifically:

"Removal of data object's dependency on algorithm and executive"

As innocent as this sounds, it is a beast. Below is a list of some of
the functions I removed from vtkDataObject.

int ShouldIReleaseData();
vtkGetMacro(DataReleased,int);
void SetReleaseDataFlag(int);
virtual void Update();
virtual void UpdateInformation();
virtual unsigned long GetEstimatedMemorySize();
virtual void SetUpdateExtent(int piece,int numPieces, int ghostLevel);
virtual int* GetUpdateExtent();
unsigned long GetPipelineMTime();
void SetUpdatePiece(int piece);
void SetUpdateNumberOfPieces(int num);
virtual int GetUpdatePiece();
virtual int GetUpdateNumberOfPieces();
virtual int* GetWholeExtent();
void SetExtentTranslator(vtkExtentTranslator* translator);
vtkExtentTranslator* GetExtentTranslator();

Every single one of the functions above access the pipeline
information and hence depend on the algorithm and executive. So what
does this mean? It means that if you have a filter that does this:

input->GetWholeExtent();

it now has to do:

inInfo->Get(vtkStreamingDemandDrivenPipeline::WHOLE_EXTENT());

If you do:

outputData->Update();

you now have to do:

algorithm->Update();

These are all small changes but there seems to be lots of places in
VTK that need to be changed. Specially in the Imaging kit. I changed a
couple of dozens of classes already. When the entire VTK compiles, I
will commit these changes to my Gitorious repo.

Also, there are some behavior changes that may require a close look at
existing code. For example, vtkImageData::SetScalarType() and
vtkImageData::SetNumberOfScalarComponents() currently set meta-data in
the pipeline information - vtkImageData does not have a "ScalarType"
or "NumberOfScalarComponents" member. I will change these to set the
type of the actual scalars, i.e. something like:

void SetScalarType(int type)
{
  vtkDataArray* scalars = vtkDataArray::CreateDataArray(type);
  this->GetPointData()->SetScalars(scalars);
  ...
}

With the proper checks, of course. This means that these functions
should never NEVER be used in RequestInformation(). As long as they
are used in RequestData(), everything should work as before. So this
will work as before:

image->SetScalarType(VTK_FLOAT);
image->SetNumberOfScalarComponents(3);
image->SetExtent(...);
image->AllocateScalars();

-berk