[vtk-developers] changes in temporal support in VTK

[Moreland, Kenneth]

The change sounds OK to me.  Although this class seemed like a natural thing to do when implementing temporal support, it has caused problems in unexpected ways.

I recommend flipping the order in which you implement this change.  First change all filters to not use vtkTemporalDataSet and replace that with CONTINUE_EXECUTION.  Make sure that the implementation is plausible, straightforward enough for users to implement, solve the problems we see with the current implementation, and don't introduce new weird problems.  After that remove vtkTemporalDataSet and the auto pipeline iteration, which at this point should be trivial.

-Ken

From: Yuanxin Liu <leo.liu at kitware.com<mailto:leo.liu at kitware.com>>
Date: Friday, April 27, 2012 11:40 AM
To: VTK Developers <vtk-developers at vtk.org<mailto:vtk-developers at vtk.org>>
Cc: Kitware-developers <kitware-developers at kitware.com<mailto:kitware-developers at kitware.com>>
Subject: [EXTERNAL] [vtk-developers] changes in temporal support in VTK

Hi,
  We are currently considering a few backward-incompatible changes to the temporal support in the VTK pipeline and would like to hear comments.  We are also interested in hearing other suggestions to improve handling of time-dependent data.

  The main change is to remove the use of vtkTemporalDataSet and to limit the time request to be a single time step, i.e.

  *   Currently, a filter can request objects from multiple time steps by setting the key UPDATE_TIME_STEPS to a vector of doubles; the resulting objects get wrapped by the pipeline into a single vtkTemporalDataSet object.
  *   After the change, a filter can only request a single time step by setting the key UPDATE_TIME_STEP to a single double.  The "wrapping" no longer happens.

  For existing filters that depend on multiple time steps,  we will modify them to use the CONTINUE_EXECUTION key to iteratively execute the pipeline and store the objects from the iterations.   There will be super classes/utility classes to make this easy.

  The main motivation is that, by pushing the temporal functionality from the core pipeline to the filters, the execution pipeline becomes simpler and easier to maintain. Some bugs, e.g.( ParaView bug Id=6662<http://www.paraview.org/Bug/view.php?id=6662>) will go away as a result.

Leo
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