Getting the number of components (or the number of flattened components)
from an `ArrayHandle` is usually trivial. However, if the `ArrayHandle` is
special in that the number of components is specified at runtime, then it
becomes much more difficult to determine.
Getting the number of components is most important when extracting
component arrays (or reconstructions using component arrays) with
`UnknownArrayHandle`. Previously, `UnknownArrayHandle` used a hack to get
the number of components, which mostly worked but broke down when wrapping
a runtime array inside another array such as `ArrayHandleView`.
To prevent this issue, the ability to get the number of components has been
added to `ArrayHandle` proper. All `Storage` objects for `ArrayHandle`s now
need a method named `GetNumberOfComponentsFlat`. The implementation of this
method is usually trivial. The `ArrayHandle` template now also provides a
`GetNumberOfComponentsFlat` method that gets this information from the
`Storage`. This provides an easy access point for the `UnknownArrayHandle`
to pull this information.
The `VecTraits` class allows templated functions, methods, and classes to
treat type arguments uniformly as `Vec` types or to otherwise differentiate
between scalar and vector types. This only works for types that `VecTraits`
is defined for.
The `VecTraits` templated class now has a default implementation that will
be used for any type that does not have a `VecTraits` specialization. This
removes many surprise compiler errors when using a template that, unknown
to you, has `VecTraits` in its implementation.
One potential issue is that if `VecTraits` gets defined for a new type, the
behavior of `VecTraits` could change for that type in backward-incompatible
ways. If `VecTraits` is used in a purely generic way, this should not be an
issue. However, if assumptions were made about the components and length,
this could cause problems.
Fixes#589
The `UnknownArrayHandle` has been updated to allow
`ArrayHandleRuntimeVec` to work interchangeably with basic
`ArrayHandle`. If an `ArrayHandleRuntimeVec` is put into an
`UnknownArrayHandle`, it can be later retrieved as an `ArrayHandleBasic`
as long as the base component type matches and it has the correct amount
of components. This means that an array can be created as an
`ArrayHandleRuntimeVec` and be used with any filters or most other
features designed to operate on basic `ArrayHandle`s. Likewise, an array
added as a basic `ArrayHandle` can be retrieved in an
`ArrayHandleRuntimeVec`. This makes it easier to pull arrays from VTK-m
and place them in external structures (such as `vtkDataArray`).
The new `ArrayHandleRuntimeVec` is a fancy `ArrayHandle` allows you to
specify a basic array of `Vec`s where the number of components of the `Vec`
are not known until runtime. (It can also optionally specify scalars.) The
behavior is much like that of `ArrayHandleGroupVecVariable` except that its
representation is much more constrained. This constrained representation
allows it to be automatically converted to an `ArrayHandleBasic` with the
proper `Vec` value type. This allows one part of code (such as a file
reader) to create an array with any `Vec` size, and then that array can be
fed to an algorithm that expects an `ArrayHandleBasic` of a certain value
type.
