CMAKE: Migrate to ITK 6 modern interface library targets

CMake/ElastixITKDeps.cmake

@@ -0,0 +1,102 @@
+#
+# ElastixITKDeps.cmake
+#
+# Provides a helper macro and convenience variables for linking ITK dependencies
+# using modern CMake interface library targets (ITK 6+) or the legacy
+# ${ITK_LIBRARIES} variable (ITK 5.x), maintaining backward compatibility.
+#
+# Must be included AFTER find_package(ITK ...) and, for ITK 6+, after
+# itk_generate_factory_registration() has been called so that factory
+# meta-module target properties are properly configured.
+#
+# Variables set by this file
+# --------------------------
+#
+#   ELASTIX_ITK_EXECUTABLE_LIBRARIES
+#     For executables that already carry ITK processing module dependencies
+#     transitively via elxCommon (e.g. elastix_exe, transformix_exe, GTest targets).
+#     ITK 6+: IO factory meta-module targets (ITK::ITKImageIO, etc.) that provide
+#             the factory registration include directories and compile definitions.
+#     ITK 5.x: ${ITK_LIBRARIES} (factory registration handled globally by UseITK.cmake).
+#
+#   ELASTIX_ITK_ALL_LIBRARIES
+#     For standalone executables that do NOT link elxCommon/elxCore and therefore
+#     need explicit ITK processing module dependencies as well as IO factories
+#     (e.g. elxComputeOverlap, elxImageCompare, external project examples).
+#     ITK 6+: ${ITK_INTERFACE_LIBRARIES} (all requested module interface libs)
+#             plus IO factory meta-module targets.
+#     ITK 5.x: ${ITK_LIBRARIES}.
+#
+# Macro provided
+# --------------
+#
+#   elastix_link_itk(<target> [PUBLIC|PRIVATE|INTERFACE] MODULES <mod1> [<mod2> ...])
+#
+#   Links <target> to specific ITK modules using:
+#     ITK 6+: ITK::<mod>Module interface library targets
+#     ITK 5.x: ${ITK_LIBRARIES} (all loaded modules)
+#
+#   The optional scope keyword (PUBLIC / PRIVATE / INTERFACE) controls CMake
+#   link visibility and may be omitted for old-style plain linkage.
+#
+#   Example (library that exposes ITK types in its public headers):
+#     elastix_link_itk(elxCommon PUBLIC MODULES
+#       ITKCommon ITKTransform ITKOptimizers ITKRegistrationCommon)
+#
+#   Example (internal library with no public ITK API):
+#     elastix_link_itk(param MODULES ITKCommon)
+#
+
+if(ITK_VERSION_MAJOR GREATER_EQUAL 6)
+  # Collect IO factory meta-module targets configured by itk_generate_factory_registration().
+  # These carry INTERFACE_INCLUDE_DIRECTORIES pointing to the generated factory
+  # registration headers and INTERFACE_COMPILE_DEFINITIONS enabling the managers.
+  set(ELASTIX_ITK_EXECUTABLE_LIBRARIES "")
+  foreach(_elx_meta ITKImageIO ITKTransformIO ITKMeshIO)
+    if(TARGET ITK::${_elx_meta})
+      list(APPEND ELASTIX_ITK_EXECUTABLE_LIBRARIES ITK::${_elx_meta})
+    endif()
+  endforeach()
+  unset(_elx_meta)
+
+  # ITKTestKernel provides test utilities (itkTestingComparisonImageFilter.h, etc.).
+  # Linked only to test targets; not added to production libraries.
+  if(TARGET ITK::ITKTestKernelModule)
+    set(ELASTIX_ITK_TEST_LIBRARIES ITK::ITKTestKernelModule)
+  else()
+    set(ELASTIX_ITK_TEST_LIBRARIES "")
+  endif()
+
+  # Full ITK: all requested module interface libraries + IO factory meta-modules.
+  # ITK_INTERFACE_LIBRARIES is set by itk_module_config() in ITKConfig.cmake
+  # and contains one ITK::<mod>Module target per loaded ITK module.
+  set(ELASTIX_ITK_ALL_LIBRARIES ${ITK_INTERFACE_LIBRARIES} ${ELASTIX_ITK_EXECUTABLE_LIBRARIES})
+
+else()
+  # ITK 5.x: the single ${ITK_LIBRARIES} variable covers all requested modules
+  # and IO factories (factory registration is done globally by UseITK.cmake).
+  set(ELASTIX_ITK_EXECUTABLE_LIBRARIES ${ITK_LIBRARIES})
+  set(ELASTIX_ITK_TEST_LIBRARIES "")
+  set(ELASTIX_ITK_ALL_LIBRARIES ${ITK_LIBRARIES})
+endif()
+
+#
+# elastix_link_itk(<target> [PUBLIC|PRIVATE|INTERFACE] MODULES <mod1> [<mod2> ...])
+#
+macro(elastix_link_itk _elt_target)
+  cmake_parse_arguments(_elt "" "" "MODULES" ${ARGN})
+  # _elt_UNPARSED_ARGUMENTS holds an optional scope keyword (PUBLIC/PRIVATE/INTERFACE).
+  if(ITK_VERSION_MAJOR GREATER_EQUAL 6)
+    set(_elt_itk_link_targets "")
+    foreach(_elt_mod ${_elt_MODULES})
+      list(APPEND _elt_itk_link_targets ITK::${_elt_mod}Module)
+    endforeach()
+    target_link_libraries(${_elt_target} ${_elt_UNPARSED_ARGUMENTS} ${_elt_itk_link_targets})
+    unset(_elt_itk_link_targets)
+    unset(_elt_mod)
+  else()
+    target_link_libraries(${_elt_target} ${_elt_UNPARSED_ARGUMENTS} ${ITK_LIBRARIES})
+  endif()
+  unset(_elt_MODULES)
+  unset(_elt_UNPARSED_ARGUMENTS)
+endmacro()

CMakeLists.txt

@@ -86,7 +86,20 @@ find_package(ITK 5.4.1 REQUIRED COMPONENTS
     ${_GPU_depends}
     ${_ITK_io_depends}
     )
-include(${ITK_USE_FILE})
+
+if(ITK_VERSION_MAJOR GREATER_EQUAL 6)
+  # ITK 6+: use modern interface library targets.
+  # itk_generate_factory_registration() configures the factory registration
+  # headers and sets INTERFACE properties on the factory meta-module targets
+  # (ITK::ITKImageIO, ITK::ITKTransformIO, ITK::ITKMeshIO).
+  # Must be called before any add_subdirectory() so the target properties are
+  # ready when subdirectory CMakeLists.txt files reference them.
+  itk_generate_factory_registration()
+else()
+  # ITK 5.x: UseITK.cmake sets global include/link directories and calls
+  # itk_generate_factory_registration() internally.
+  include(${ITK_USE_FILE})
+endif()
 
 #---------------------------------------------------------------------
 # Add the CMake dir as an additional module path,
@@ -100,6 +113,10 @@ include(elastixVersion)
 # Function for exporting targets
 include(elastixExportTarget)
 
+# ITK dependency helper: provides elastix_link_itk() macro and
+# ELASTIX_ITK_EXECUTABLE_LIBRARIES / ELASTIX_ITK_ALL_LIBRARIES variables.
+include(ElastixITKDeps)
+
 if (MSVC)
   add_compile_options(/W3)
 else()

Common/CMakeLists.txt

@@ -214,8 +214,32 @@ endif()
 #---------------------------------------------------------------------
 # Link against other libraries.
 
-target_link_libraries(elxCommon
-  ${ITK_LIBRARIES}
+elastix_link_itk(elxCommon PUBLIC MODULES
+  ITKCommon
+  ITKDisplacementField
+  ITKDistanceMap
+  ITKImageCompose
+  ITKImageFilterBase
+  ITKImageFunction
+  ITKImageGradient
+  ITKImageGrid
+  ITKImageIntensity
+  ITKImageStatistics
+  ITKIOImageBase
+  ITKIOMeshBase
+  ITKIOMeta
+  ITKIOTransformBase
+  ITKIOXML
+  ITKMathematicalMorphology
+  ITKMesh
+  ITKOptimizers
+  ITKRegistrationCommon
+  ITKSmoothing
+  ITKSpatialObjects
+  ITKStatistics
+  ITKThresholding
+  ITKTransform
+  ITKTransformFactory
 )
 
 target_include_directories(elxCommon PUBLIC

Common/GTesting/CMakeLists.txt

@@ -39,14 +39,14 @@ if (ITK_VERSION VERSION_LESS_EQUAL 5.4.5)
   target_link_libraries(CommonGTest
     GTest::GTest
     GTest::Main
-    ${ITK_LIBRARIES}
+    ${ELASTIX_ITK_EXECUTABLE_LIBRARIES}
     elastix_lib
   )
 else()
   target_link_libraries(CommonGTest
     GTest::gtest
     GTest::gtest_main
-    ${ITK_LIBRARIES}
+    ${ELASTIX_ITK_EXECUTABLE_LIBRARIES}
     elastix_lib
   )
 endif()

Common/MevisDicomTiff/CMakeLists.txt

@@ -24,7 +24,11 @@ if(NOT ELASTIX_NO_INSTALL_DEVELOPMENT)
     COMPONENT Development)
 endif()
 
-target_link_libraries(mevisdcmtiff ${ITK_LIBRARIES})
+elastix_link_itk(mevisdcmtiff MODULES
+  ITKCommon
+  ITKGDCM
+  ITKIOImageBase
+)
 target_include_directories(mevisdcmtiff PUBLIC
   $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
   $<INSTALL_INTERFACE:${ELASTIX_INCLUDE_DIR}/Common/MevisDicomTiff>)

Common/OpenCL/CMakeLists.txt

@@ -56,10 +56,15 @@ set(OpenCL_Files
 add_library(elxOpenCL STATIC ${OpenCL_Files})
 
 # Link it against the necessary libraries.
-target_link_libraries(elxOpenCL
-  ${ITK_LIBRARIES}
-  ${OPENCL_LIBRARIES}
+elastix_link_itk(elxOpenCL MODULES
+  ITKCommon
+  ITKGPUCommon
+  ITKTransform
+  ITKImageGrid
+  ITKSmoothing
+  ITKImageFunction
 )
+target_link_libraries(elxOpenCL ${OPENCL_LIBRARIES})
 
 target_include_directories(elxOpenCL PUBLIC ${OPENCL_INCLUDE_DIRS})
 target_compile_definitions(elxOpenCL PUBLIC ELASTIX_USE_OPENCL)

Common/ParameterFileParser/CMakeLists.txt

@@ -17,7 +17,9 @@ if(NOT ELASTIX_NO_INSTALL_DEVELOPMENT)
     COMPONENT Development)
 endif()
 
-target_link_libraries(param ${ITK_LIBRARIES})
+elastix_link_itk(param MODULES
+  ITKCommon
+)
 target_include_directories(param PUBLIC
   $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
   $<INSTALL_INTERFACE:${ELASTIX_INCLUDE_DIR}/Common/ParameterFileParser>)

Components/CMakeLists.txt

@@ -5,10 +5,22 @@ project(elxComponents)
 
 #---------------------------------------------------------------------
 # Set the libraries to be linked.
-
-set(elxLinkLibs
-  elxCore
-  ${ITK_LIBRARIES})
+#
+# For ITK 6+, component libraries inherit all ITK processing module dependencies
+# transitively via elxCore -> elxCommon (PUBLIC link). No additional direct
+# ITK module link is needed here.
+# For ITK 5.x, ${ITK_LIBRARIES} provides full coverage (factory registration
+# is handled globally by UseITK.cmake).
+if(ITK_VERSION_MAJOR GREATER_EQUAL 6)
+  set(elxLinkLibs
+    elxCore
+  )
+else()
+  set(elxLinkLibs
+    elxCore
+    ${ITK_LIBRARIES}
+  )
+endif()
 
 #--------------------------------------------------------------------
 # Prepare elxInstallComponentFunctionDeclarations.h and

Components/Metrics/KNNGraphAlphaMutualInformation/KNN/CMakeLists.txt

@@ -36,7 +36,12 @@ add_subdirectory(ann_1.1)
 add_library(KNNlib STATIC ${KNN_Files})
 
 # Link it against the necessary libraries.
-target_link_libraries(KNNlib ANNlib ${ITK_LIBRARIES})
+elastix_link_itk(KNNlib MODULES
+  ITKCommon
+  ITKStatistics
+  ITKSpatialObjects
+)
+target_link_libraries(KNNlib ANNlib)
 
 # Group in IDE's like Visual Studio
 set_property(TARGET KNNlib PROPERTY FOLDER "libraries")

Core/CMakeLists.txt

@@ -185,13 +185,20 @@ elastix_export_target(param)
 # Define the mevis dcm tiff lib to which we should link.
 set(mevisdcmtifflib mevisdcmtiff)
 
+# For ITK 6+: executables link to the IO factory meta-module targets which carry
+# INTERFACE_INCLUDE_DIRECTORIES pointing to the generated factory registration
+# headers (itkImageIOFactoryRegisterManager.h, etc.) and INTERFACE_COMPILE_DEFINITIONS
+# enabling the registration managers. ELASTIX_ITK_EXECUTABLE_LIBRARIES is set
+# by CMake/ElastixITKDeps.cmake (included from the top-level CMakeLists.txt).
+# For ITK 5.x: ${ITK_LIBRARIES} is used (factory registration handled globally
+# by UseITK.cmake via directory-scoped COMPILE_DEFINITIONS).
 set(ELASTIX_TARGET_LINK_LIBRARIES
   param
   elxCommon
   elxCore
   ${mevisdcmtifflib}
   ${AllComponentLibs}
-  ${ITK_LIBRARIES}
+  ${ELASTIX_ITK_EXECUTABLE_LIBRARIES}
 )
 if(ELASTIX_USE_OPENCL)
   set(ELASTIX_TARGET_LINK_LIBRARIES  ${ELASTIX_TARGET_LINK_LIBRARIES} elxOpenCL)

Core/Main/GTesting/CMakeLists.txt

@@ -18,15 +18,15 @@ if (ITK_VERSION VERSION_LESS_EQUAL 5.4.5)
     GTest::Main
     elastix_lib
     transformix_lib
-    ${ITK_LIBRARIES}
+    ${ELASTIX_ITK_EXECUTABLE_LIBRARIES}
   )
 else()
   target_link_libraries(ElastixLibGTest
     GTest::gtest
     GTest::gtest_main
     elastix_lib
     transformix_lib
-    ${ITK_LIBRARIES}
+    ${ELASTIX_ITK_EXECUTABLE_LIBRARIES}
   )
 endif()
 

ElastixConfig.cmake.in

@@ -25,6 +25,16 @@ if(NOT ITK_CONFIG_TARGETS_FILE)
   find_package(ITK "@ITK_VERSION@" EXACT REQUIRED)
 endif()
 
+# For ITK 6+: generate factory registration headers and configure factory
+# meta-module target properties in the downstream project's build scope.
+# Guards against double-invocation if the downstream project also calls this.
+if(NOT ELASTIX_ITK_FACTORY_REGISTRATION_DONE)
+  set(ELASTIX_ITK_FACTORY_REGISTRATION_DONE TRUE)
+  if(ITK_VERSION_MAJOR GREATER_EQUAL 6 AND COMMAND itk_generate_factory_registration)
+    itk_generate_factory_registration()
+  endif()
+endif()
+
 
 # Import ELASTIX targets.
 set( ELASTIX_CONFIG_TARGETS_FILE "${_ELASTIXConfig_DIR}/ElastixTargets.cmake")

Testing/CMakeLists.txt

@@ -73,7 +73,8 @@ macro(elx_add_test_core executable_name source_name test_name group)
       param               # some test use the CommandLineArgumentParser
       elxCommon            # provides Common headers (Transforms, CostFunctions, etc.)
       ${mevisdcmtifflib}  # is empty if not selected in CMake
-      ${ITK_LIBRARIES}
+      ${ELASTIX_ITK_EXECUTABLE_LIBRARIES}
+      ${ELASTIX_ITK_TEST_LIBRARIES}
     )
 
     if(ELASTIX_USE_OPENCL)
@@ -420,22 +421,22 @@ endmacro()
 
 # Create elxComputeOverlap
 add_executable(elxComputeOverlap elxComputeOverlap.cxx itkCommandLineArgumentParser.cxx)
-target_link_libraries(elxComputeOverlap ${ITK_LIBRARIES})
+target_link_libraries(elxComputeOverlap ${ELASTIX_ITK_ALL_LIBRARIES})
 set_property(TARGET elxComputeOverlap PROPERTY FOLDER "tests/Executable")
 
 # Create elxImageCompare
 add_executable(elxImageCompare elxImageCompare.cxx itkCommandLineArgumentParser.cxx)
-target_link_libraries(elxImageCompare ${ITK_LIBRARIES})
+target_link_libraries(elxImageCompare ${ELASTIX_ITK_ALL_LIBRARIES})
 set_property(TARGET elxImageCompare PROPERTY FOLDER "tests/Executable")
 
 # Create elxTransformParametersCompare
 add_executable(elxTransformParametersCompare elxTransformParametersCompare.cxx itkCommandLineArgumentParser.cxx)
-target_link_libraries(elxTransformParametersCompare elxCore param ${ITK_LIBRARIES})
+target_link_libraries(elxTransformParametersCompare elxCore param ${ELASTIX_ITK_EXECUTABLE_LIBRARIES})
 set_property(TARGET elxTransformParametersCompare PROPERTY FOLDER "tests/Executable")
 
 # Create elxInvertTransform
 add_executable(elxInvertTransform elxInvertTransform.cxx itkCommandLineArgumentParser.cxx)
-target_link_libraries(elxInvertTransform elxCore param ${ITK_LIBRARIES})
+target_link_libraries(elxInvertTransform elxCore param ${ELASTIX_ITK_EXECUTABLE_LIBRARIES})
 set_property(TARGET elxInvertTransform PROPERTY FOLDER "tests/Executable")
 
 #---------------------------------------------------------------------

UseElastix.cmake.in

@@ -6,6 +6,12 @@
 # find_package( Elastix REQUIRED )
 # include( ${ELASTIX_USE_FILE} )
 #
+# Note: for ITK 6+, prefer linking directly to the 'elastix_lib' or
+# 'transformix_lib' CMake targets instead of using this file.  Modern
+# targets carry include directories, compile definitions, and all ITK
+# interface library dependencies as transitive INTERFACE properties,
+# so include_directories() and link_directories() are no longer needed.
+#
 
 # Add include dirs
 include_directories( ${ELASTIX_INCLUDE_DIRS} )