WIP: ENH: Adjust RTK applications and example to modern CMake interface

[SimonRit]

See
https://docs.itk.org/en/latest/migration_guides/itk_6_migration_guide.html#migration-for-itk-modules for a detailed explanation.

[SimonRit]

This currently does not work, it does not register ITK factories for an unknown reason. When executing rtkfdk with an .mha output, I get

ExceptionObject caught with itk::WriteImage(streamerBP->GetOutput(), args_info.output_arg) in file /home/srit/src/rtk/rtk/applications/rtkfdk/rtkfdk.cxx line 207

itk::ImageFileWriterException (0x60b925e7f650)
Location: "unknown" 
File: /home/srit/src/itk/itk/Modules/IO/ImageBase/include/itkImageFileWriter.hxx
Line: 117
Description:  Could not create IO object for writing file fdk.mha
  Tried to create one of the following:
    HndImageIO
    HncImageIO
    XimImageIO
    HisImageIO
    ImagXImageIO
    DCMImagXImageIO
    EdfImageIO
    XRadImageIO
    OraImageIO
    HndImageIO
    HncImageIO
    XimImageIO
    HisImageIO
    ImagXImageIO
    DCMImagXImageIO
    EdfImageIO
    XRadImageIO
    OraImageIO
    GDCMImageIO
  You probably failed to set a file suffix, or
    set the suffix to an unsupported type.

If I rollback to using include(${ITK_USE_FILE}) in applications/CMakeLists.txt, it does work so there must be something in UseITK.cmake missing in my code. Any pointer is welcome @blowekamp.

[SimonRit]

In the latest force push, I added this code copy pasted from UseITK.cmake. Then, RTK's applications work. However, the examples (external applications using RTK) still fail due to missing factories so something's not right and I don't know what.

[blowekamp]

Thank you for trying out the latest changed in ITK right away.

You may want to create a linking function or some variables to avoid the duplicated conditionings.

I was uncertain what to run to reproduce your error messages.

[blowekamp]

You were previously linking to all loaded ITK modules, and presumably using them with "UseITK".

Using ITK_INTERFACE_LIBRARIES will apply properties and line to all the ITK::{module-name}Module loaded in the find_package. This may include additional modules no specified as dependents of just the RTK Module.

[blowekamp]

The migration guide contains some information on "Factory Registration with Meta Modules": https://docs.itk.org/en/latest/migration_guides/itk_6_migration_guide.html#application-configuration

The docs are missing that an application should also link to the meta-module "ITK::ITKImageIO". These meta-module have the properties of the include and compile definitions in them so they don't need to be set in at a directory/global level.

[SimonRit]

Thanks, I have just force-pushed a new version which works. I am not entirely convinced though. Can I make the target RTKModule dependent on ITK::ITKImageIO and ITK::ITKFFTImageFilterInit to avoid having to specify it in each application and example?

By the way, the doc mentions ITKIOFFT which does not exist, I have used ITKFFTImageFilterInit instead.

Thanks again for you support!