The `From` and `To` nomenclature for topology mapping has been confusing for
both users and developers, especially at lower levels where the intention of
mapping attributes from one element to another is easily conflated with the
concept of mapping indices (which maps in the exact opposite direction).
These identifiers have been renamed to `VisitTopology` and `IncidentTopology`
to clarify the direction of the mapping. The order in which these template
parameters are specified for `WorkletMapTopology` have also been reversed,
since eventually there may be more than one `IncidentTopology`, and having
`IncidentTopology` at the end will allow us to replace it with a variadic
template parameter pack in the future.
Other implementation details supporting these worklets, include `Fetch` tags,
`Connectivity` classes, and methods on the various `CellSet` classes (such as
`PrepareForInput` have also reversed their template arguments. These will need
to be cautiously updated.
The convenience implementations of `WorkletMapTopology` have been renamed for
clarity as follows:
```
WorkletMapPointToCell --> WorkletVisitCellsWithPoints
WorkletMapCellToPoint --> WorkletVisitPointsWithCells
```
The `ControlSignature` tags have been renamed as follows:
```
FieldInTo --> FieldInVisit
FieldInFrom --> FieldInMap
FromCount --> IncidentElementCount
FromIndices --> IncidentElementIndices
```
These changes now allow VTK-m to compile on CUDA 7.5 by using const arrays,
when compiling with CUDA 8+ support we upgrade to static const arrays, and
lastly when CUDA is disabled we fully elevate to static constexpr.
If a global static array is declared with VTKM_EXEC_CONSTANT and the code
is compiled by nvcc (for multibackend code) then the array is only accesible
on the GPU. If for some reason a worklet fails on the cuda backend and it is
re-executed on any of the CPU backends, it will continue to fail.
We couldn't find a simple way to declare the array once and have it available
on both CPU and GPU. The approach we are using here is to declare the arrays
as static inside some "Get" function which is marked as VTKM_EXEC_CONT.
Sandia National Laboratories recently changed management from the
Sandia Corporation to the National Technology & Engineering Solutions
of Sandia, LLC (NTESS). The copyright statements need to be updated
accordingly.
