The original design of the filter base class required several specialized
base classes to control what information was pulled from the input
`DataSet` and provided to the derived class. Since the filter base class was
redesigned, the derived classes all get a `DataSet` and pull their own
information from it. Thus, most specialized filter base classes became
unnecessary and removed.
The one substantial exception was the `FilterField`. This filter base class
managed input and output arrays. This was kept separate from the base
`Filter` because not all filters need the ability to select this
information.
That said, this separation has not been particularly helpful. There are
several other features of `Filter` that does not apply to all subclasses.
Furthermore, there are several derived filters that are using `FilterField`
merely to pick a single part, like selecting a coordinate system, and
ignoring the rest of the abilities.
Thus, it makes more sense to deprecate `FilterField` and have these classes
inherit directly from `Filter`.
While updating the user's guide, I noticed a couple of minor problems
with how filters map fields. First, if a filter was using
`CreateResultCoordinateSystem`, it did not respect the
`PassCoordinateSystems` flag. Second, if both an `initializer_list` and
a mode was given to `SetFieldsToPass`, the mode was captured
incorrectly. Both problems are corrected.
During the VTK-m 1.8 and 1.9 development, the filter infrastructure was
overhauled. Part of this created a completely new set of base classes. To
avoid confusion with the original filter base classes and ease transition,
the new filter base classes were named `NewFilter*`. Eventually after all
filters were transitioned, the old filter base classes were deprecated.
With the release of VTK-m 2.0, the old filter base classes are removed. The
"new" filter base classes are no longer new. Thus, they have been renamed
simply `Filter` (and `FilterField`).
