Originally, most of the sources used constructor parameters to set the
various options of the source. Although convenient, it was difficult to
keep track of what each parameter meant. To make the code more clear,
source parameters are now set with accessor functions (e.g.
`SetPointDimensions`). Although this makes code more verbose, it helps
prevent mistakes and makes the changes more resilient to future changes.
The `Tangle` source would create a point field generically named
`nodevar`. This name was not indicitive of the data or its source. Thus,
the output point field has been renamed `tangle`.
The `Tangle` source was also creating a cell field (named `cellvar`).
This field was really just a mirror of the cell indices (counting from 0
on up). This field has been removed from the input. If you want such a
field, you can now use the `GenerateIds` filter to add it to any data
set.
By leveraging WorkletVisitPointsWithCells we can get already
pre-computed i,j,k locations helping with performance
In addition we have made the algorithm easier to read by
leveraging VTK-m Vec types.
`vtkm::source::Source` now uses virtual inheritance for
the `Execute` method. This will allow us to enforce that
all vtkm::source have a consistent calling convention.
To make the code inside filters and sources more similar the
base `vtkm::source::Source` class has a `vtkm::cont::Invoker`
as a member variable. This will allow sources to use the
`this->Invoke()` pattern that filters use to launch worklets.
