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
Whan an `UnknownArrayHandler` is constructed from an `ArrayHandle`, it uses
the `VecTraits` of the component type to construct its internal functions.
This meant that you could not put an `ArrayHandle` with a component type
that did not have `VecTraits` into an `UnknownArrayHandle`.
`UnknownArrayHandle` now no longer needs the components of its arrays to
have `VecTraits`. If the component type of the array does not have
`VecTraits`, it treats the components as if they are a scalar type.
Before, `ArrayExtractComponent` only worked with `Vec` types. Anything
that was not specifically a `Vec` was assumed to be a basic component
even if it had `VecTraits`. This was changed to extract components out
of anything that has `VecTraits`. The assumption is that all components
of the Vec-like object are packed tightly in the object.
This allows `ArrayExtractComponent` to work with objects like
`vtkm::Range` and `vtkm::Bounds` and extract their parts as expected.
Many arrays decorate other arrays but still allow an efficient component
extraction. However, the component can only be extracted if it can be
efficiently extracted from the array being decorated. In this case, the
array reported that it could efficiently extract even though it could
not.
Fixed this by having the `ArrayExtractComponentImpl` classes inherit
from the respective superclass. This will in turn inhert the
`ArrayExtractComponentImplInefficient` if it is the base class.
To avoid having to use a device compiler every time you wish to use
`ArrayGetValue`, the actual implementation is compiled into the `vtkm_cont`
library. To allow this to work for all the templated versions of
`ArrayHandle`, the implementation uses the extract component features of
`UnknownArrayHandle`. This works for most common arrays, but not all
arrays.
For arrays that cannot be directly represented by an `ArrayHandleStride`,
the fallback is bad. The entire array has to be pulled to the host and then
copied serially to a basic array.
For `ArrayGetValue`, this is just silly. So, for arrays that cannot be
simply represented by `ArrayHandleStride`, make a fallback that just uses
`ReadPortal` to get the data. Often this is not the most efficient method,
but it is better than the current alternative.
The typical use case of `ArrayHandleStride` is to flexibly point into
another array, often looking at a single component in an array. It is
typical that multiple things will be accessing the same array, and bad
things could happen as they all try to resize. There was some code to
try to figure out what the size of the original array was, but it was
fragile.
It is safer for now to disable the behavior altogether. If a use case
pops up, we can reintroduce the code.
`ArrayExtractComponent` allows you to get a component of an array.
Unlike `ArrayHandleExtractComponent`, the type you get is always the
same: an `ArrayHandleStride`. This way, you can get an array that
contains the data of an extracted component with less templating and
potentially dramatically reduce the amount of code generated (although
some runtime integer arithmetic is added).
