[vtkusers] Update on VTK 4 compatibility removal

[Berk Geveci]

Hi folks,

I made some more progress on removing the VTK 4 compatibility layer. The
goals of this work are described here:

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

I am going to regularly send updates to mailing list so that folks can
try out these changes and see if they need to update their own software. For
now,  I am publishing a branch called remove-vtk-4-compatibility to
https://gitorious.org/~berkgeveci/kitware/berkgevecis-vtk. In the
future, there will be a branch in the VTK stage as well. As of my last
changes, the entire VTK compiles on my Mac. There are plenty of test failures
so I wouldn't consider it stable. I would not use it for anything other than
gauge the progress of the work and to see the changes that are coming.

For a description of my first pass, see my previous e-mail to this list
title "Started on VTK 4 compatibility removal". My changes in this pass
(commits 5de4d8854f7e - 4672b5607613a) include:

- I removed the following methods from vtkDataObject (omitting methods
that are not very relevant):

Update()
UpdateInformation()
PropagateUpdateExtent()
SetUpdateExtent() (all variations)
SetUpdateXXX() (all variations)
GetUpdateExtent() (all variations)
GetUpdateXXX() (all variations)
SetWholeExtent()
GetWholeExtent()
SetMaximumNumberOfPieces()
GetMaximumNumberOfPieces()
GetExtentTranslator()
GetPipelineMTime()

The first 3 of these were the most popular and caused me to update most
code in VTK. The fixes are pretty simple. This:

filter->GetOutput()->Update()

changed to:

filter->Update()

This applies to Update(), UpdateInformation() and PropagateUpdateExtent().

There was also a lot of this:

filter->GetInput()->Update()

which can now be rewritten as

filter->GetInputAlgorithm()->Update()

The second most popular set was SetUpdateExtent() and GetWholeExtent().
They are also pretty easy to fix. However, be warned that how to fix it
depends on the context. If you are in a RequestXXX() method (where XXX
can be any of Information, UpdateExtent or Data), do NOT call

this->GetInput()->GetWholeExtent()

Instead, do

vtkInformation* inInfo = inputVector[0]->GetInformationObject(0);
const int* wext = inInfo->Get(
  vtkStreamingDemandDrivenPipeline::WHOLE_EXTENT());

Similarly, if you are in RequestUpdateExtent or RequestData, do NOT do:

this->GetInput()->SetUpdateExtent()

instead do:

vtkInformation* inInfo = inputVector[0]->GetInformationObject(0);
inInfo->Set(vtkStreamingDemandDrivenPipeline::UPDATE_EXTENT(), ...);

Alternatively, use the convenience functions defined in
vtkStreamingDemandDrivenPipeline (look for SetUpdateXXX).

If you are not inside a Request methods, this

filter->GetOutput()->SetUpdateExtent(...)

can now be written as

vtkStreamingDemandDrivenPipeline(filter->GetOutputInformation(), ...)

or
filter->GetOutputInformation()->Set(
  vtkStreamingDemandDrivenPipeline::UPDATE_EXTENT(), ...)

This

filter->GetOutput()->GetWholeExtent()

is now

filter->GetOutputInformation()->Get(
  vtkStreamingDemandDrivenPipeline::WHOLE_EXTENT())

Hopefully, the trend is clear by now. All meta-data and request information
have to go through information objects using various keys. All methods dealing
with meta-data and request information were removed from vtkDataObject.

- I changed the signature of all functions dealing directly with
pipeline information in
vtkImageData. These include:

SetScalarType()
GetScalarType()
SetNumberOfScalarComponents()
SetAxisUpdateExtent()
GetAxisUpdateExtent()
GetScalarTypeMin()
GetScalarTypeMax()
GetScalarSize()
Crop()

These now all take vtkInformation as an argument and made some of
these static. The most
common use of SetScalarType() and SetNumberOfScalarComponents() was:

image->SetScalarTypeToFloat();
image->SetNumberOfScalarComponents(3);
image->AllocateScalars();

I added a new version of AllocateScalars() to make this easier:

image->AllocateScalars(VTK_FLOAT, 3)

In RequestInformation, you can use the new signatures as follows:

int XXX:RequestInformation(..., vtkInformationVector* outVec)
{
  vtkInformation *outInfo = outVec->GetInformationObject(0);
  vtkImageData::SetScalarType(VTK_FLOAT, outInfo);
  vtkImageData::SetNumberOfScalarComponents(3, outInfo);
  ...
}

This is much easier then setting the values directly in outInfo since
the keys are
somewhat elaborate for array meta-data.

Again, the idea is to separate functions that deal with meta-data from functions
that directly manipulate data.

NOTE: GetScalarType() and GetNumberOfScalarComponents() are still
available but they
now work on actual data rather than meta-data. If there are no scalars
available,
they will not work correctly. I am comfortable with this change
because this seems
to be the only way these methods are used. Please let me know if you disagree.