As a programming convenience, all `vtkm::cont::DataSet` written by
`vtkm::io::VTKDataSetWriter` were written as a structured grid. Although
technically correct, it changed the structure of the data. This meant that
if you wanted to capture data to run elsewhere, it would run as a different
data type. This was particularly frustrating if the data of that structure
was causing problems and you wanted to debug it.
Now, `VTKDataSetWriter` checks the type of the `CoordinateSystem` to
determine whether the data should be written out as `STRUCTURED_POINTS`
(i.e. a uniform grid), `RECTILINEAR_GRID`, or `STRUCTURED_GRID`
(curvilinear).
Updated the image writer classes to better follow VTK-m naming
convention (i.e. use `ImageWriterPNG` instead of `PNGWriter`). The
structure of the image writer class now also better matches the
interface for the VTK writer.
Also put the implementation of the image writers into the `vtkm_io`
library so that it only has to be compiled once.
Updated the image reader classes to better follow VTK-m naming
convention (i.e. use `ImageReaderPNG` instead of `PNGReader`).
The structure of the image reader class now also better matches
the interface for the VTK reader.
Also put the implementation of the image readers into the `vtkm_io`
library so that it only has to be compiled once.
Most of this code is not templated methods. Rather, it implements over
several types to call templated functions, which creates quite a bit of
code. Rather than have all code using a reader recompile the code, just
compile it once and put it in a library.
