[CMake] find_package issues with ITK and VTK (and SlicerExecution Model)

[Williams, Norman K]

This is a problem that has been cropping up in our projects that use ITK, VTK and SlicerExecutionModel.

You won’t see it UNLESS you turn on the ITKVTK/ITKVtkGlue modules.

The problem is this: if you find packages in this order:

find_package(VTK REQUIRED)
find_package(ITK REQUIRED)

You can’t real compile anything that needs VTK, because down in the ITK deployment stuff, it calls find_package(VTK) like this:
find_package(VTK COMPONENTS
  vtkCommonCore
  vtkRenderingCore
  vtkRenderingOpenGL
  vtkRenderingFreeType
  vtkInteractionStyle
  vtkIOImage
  vtkImagingSources
  REQUIRED)

Which blows away the larger list of include directories and libraries that the first find_package(VTK REQUIRED) built.

Even better — or worse — Modules/Segmentation/LevelSetsv4Visualization/CMakeLists.txt also include find_package(VTK) — so ITK tries to import VTK twice, with different module lists.

It doesn’t even help to reverse the order:
find_package(ITK REQUIRED)
find_package(VTK REQUIRED)

because apparently there’s some hangover from the find_package(VTK) inside the ITK CMake deployment files.  The only thing that works is to use COMPONENTS, i.e.

find_package(ITK REQUIRED)
find_package(VTK COMPONENTS vtkCommonCore vtkRenderingAnnotation … REQUIRED)

Which seems to trigger a proper re-scan and build of the library/include lists.

It gets even worse if you use find_package(SlicerExecutionModel) after find_package(ITK), for the same reason — SlicerExecutionModel depends on ITK, so it clobbers the include/library lists from the first find_package(ITK).




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