vtk-m/docs/changelog/simplify-specifying-filter-allowed-value-types.md

Provide a simplified way to state allowed value types for VTK-m filters

Previously VTK-m filters used a specialization of vtkm::filter::FilterTraits<> to control the acceptable input value types. For example if the WarpVector filter want to only allow vtkm::Vec3f_32 and vtkm::Vec3f_64 it would use:

namespace vtkm { namespace filter {
template <>
class FilterTraits<WarpVector>
{
public:
  // WarpVector can only applies to Float and Double Vec3 arrays
  using InputFieldTypeList = vtkm::TypeListTagFieldVec3;
};
}}

This increase the complexity of writing filters. To make this easier VTK-m now looks for a SupportedTypes define on the filter when a vtkm::filter::FilterTraits specialization doesn't exist. This allows filters to succinctly specify supported types, such as seen below for the WarpVector filter.

class WarpVector : public vtkm::filter::FilterField<WarpVector>
{
public:
  using SupportedTypes = vtkm::TypeListTagFieldVec3;
...
};