VTK/Remove vtkTemporalDataSet

Previously, VTK pipeline supports multiple time steps in the pipeline: Filters can request data sets of multiple time steps from upstream using the key vtkStreamingDemandDrivenPipeline::UPDATE_TIME_STEPS(); Upstream sources then fulfil the request by wrapping the data sets in a vtkTemporalDataSet object and setting the key vtkDataObject::DATA_TIME_STEPS on the object. Over time, we found that the logic in the pipeline code to handle the multiple time steps is too complicated to maintain, epecially considering the limited use of it. Therefore, the temporal support has been reduced to support only single time step requets. Filters that need multiple steps still work by using the key vtkStreamingDemandPipeline::CONTINUE_EXECUTION() to loop the upstream pipeline and cache the resulting data sets. We have created a convenience super class vtkMultipleTimeStepAlgorithm that does exactly that.

In more details, the multiple time request keys:

• <source lang="cpp"> vtkInformationDoubleVectorKey* vtkStreamingDemandPipeline::UPDATE_TIME_STEPS() </source>
• <source lang="cpp"> vtkInformationDoubleVectorKey* vtkDataObject::DATA_TIME_STEPS() </source>

are replaced by single time request keys:

• <source lang="cpp"> vtkInformationDoubleKey* vtkStreamingDemandPipeline::UPDATE_TIME_STEP() </source>
• <source lang="cpp"> vtkInformationDoubleKey* vtkDataObject::DATA_TIME_STEP()</source>

As a consequence of the changes, the following constructs are no longer used and depreicated:

• <source lang="cpp"> #define VTK_TIME_EXTENT 2 </source>
• <source lang="cpp"> class vtkTemporalDataSet </source>
• <source lang="cpp"> class vtkTemporalDataSetAlgorithm </source>

After the changes, to request data sets of multiple time steps, a filter can loop the upstream pipeline by setting the key vtkStreamingDemandPipeline::CONTINUE_EXECUTION(). The simplest usage example for the key can be found in the class vtkTemporalStatistics. Another example is the class vtkMultipleTimeStepAlgorithm, which can request multiple time steps, cache the multiple data sets in a vtkMultiBlockDataSet and pass it to the child class when all the data sets are received. A filter that wants to request multiple time step data can simply inherit this class and set the key vtkMultipleTimeStepAlgorithm::UPDATE_TIME_STEPS(). An example is the class vtkTemporalInterpolator. We note that this is no more work than before the pipeline changes.