ENH: Restore ELASTIX_BUILD_EXECUTABLE CMake option

Added support for `ELASTIX_BUILD_EXECUTABLE`, allowing to switch off building the elastix and transformix executables, while still building the libraries.

Basically reverts pull request #232 commit a0c161a "STYLE: Remove ELASTIX_BUILD_EXECUTABLE option -- always build lib + exe" (August 25, 2020).

The ability to suppress building the executables appears necessary for WebAssembly support, as requested by Matt McCormick at pull request #920

CMakeLists.txt

@@ -15,6 +15,10 @@ cmake_policy(SET CMP0042 NEW) # "MACOSX_RPATH is enabled by default."
 #---------------------------------------------------------------------
 include(CTest)
 
+#---------------------------------------------------------------------
+# Allow specifying whether or not the executables are built. 
+option( ELASTIX_BUILD_EXECUTABLE "Build elastix and transformix as executable? (The libraries are always built as well anyway.)" ON )
+
   # The following may make smaller and quicker loading libraries,
   # that hides unnecessary symbols. Available from CMake 3.0.0.
   #set(CMAKE_C_VISIBILITY_PRESET hidden)

Core/CMakeLists.txt

@@ -179,20 +179,23 @@ endif()
 
 #---------------------------------------------------------------------
 # Create the elastix executable and library.
-add_executable(elastix_exe
-  Main/elastix.cxx
-  Main/elastix.h
-  Main/elxMainExeUtilities.cxx
-  Main/elxMainExeUtilities.h
-  Kernel/elxMainBase.cxx
-  Kernel/elxMainBase.h
-  Kernel/elxElastixMain.cxx
-  Kernel/elxElastixMain.h
-  ${InstallFilesForExecutables}
-)
-set_target_properties(elastix_exe PROPERTIES OUTPUT_NAME elastix)
-target_compile_definitions(elastix_exe PRIVATE ELX_CMAKE_VERSION="${CMAKE_VERSION}")
-target_link_libraries(elastix_exe ${ELASTIX_TARGET_LINK_LIBRARIES})
+
+if(ELASTIX_BUILD_EXECUTABLE)
+  add_executable(elastix_exe
+    Main/elastix.cxx
+    Main/elastix.h
+    Main/elxMainExeUtilities.cxx
+    Main/elxMainExeUtilities.h
+    Kernel/elxMainBase.cxx
+    Kernel/elxMainBase.h
+    Kernel/elxElastixMain.cxx
+    Kernel/elxElastixMain.h
+    ${InstallFilesForExecutables}
+  )
+  set_target_properties(elastix_exe PROPERTIES OUTPUT_NAME elastix)
+  target_compile_definitions(elastix_exe PRIVATE ELX_CMAKE_VERSION="${CMAKE_VERSION}")
+  target_link_libraries(elastix_exe ${ELASTIX_TARGET_LINK_LIBRARIES})
+endif()
 
 # The library type (STATIC or SHARED) is determined by the parameter
 # BUILD_SHARED_LIBS.
@@ -216,20 +219,22 @@ target_link_libraries(elastix_lib ${ELASTIX_TARGET_LINK_LIBRARIES})
 #---------------------------------------------------------------------
 # Create the transformix executable.
 
-add_executable(transformix_exe
-  Main/transformix.cxx
-  Main/elastix.h
-  Main/elxMainExeUtilities.cxx
-  Main/elxMainExeUtilities.h
-  Kernel/elxMainBase.cxx
-  Kernel/elxMainBase.h
-  Kernel/elxTransformixMain.cxx
-  Kernel/elxTransformixMain.h
-  ${InstallFilesForExecutables}
-)
-set_target_properties(transformix_exe PROPERTIES OUTPUT_NAME transformix)
-target_compile_definitions(transformix_exe PRIVATE ELX_CMAKE_VERSION="${CMAKE_VERSION}")
-target_link_libraries(transformix_exe ${ELASTIX_TARGET_LINK_LIBRARIES})
+if(ELASTIX_BUILD_EXECUTABLE)
+  add_executable(transformix_exe
+    Main/transformix.cxx
+    Main/elastix.h
+    Main/elxMainExeUtilities.cxx
+    Main/elxMainExeUtilities.h
+    Kernel/elxMainBase.cxx
+    Kernel/elxMainBase.h
+    Kernel/elxTransformixMain.cxx
+    Kernel/elxTransformixMain.h
+    ${InstallFilesForExecutables}
+  )
+  set_target_properties(transformix_exe PROPERTIES OUTPUT_NAME transformix)
+  target_compile_definitions(transformix_exe PRIVATE ELX_CMAKE_VERSION="${CMAKE_VERSION}")
+  target_link_libraries(transformix_exe ${ELASTIX_TARGET_LINK_LIBRARIES})
+endif()
 
 # The library type (STATIC or SHARED) is determined by the parameter
 # BUILD_SHARED_LIBS.
@@ -254,13 +259,13 @@ set(ELASTIX_LIBRARIES elastix_lib transformix_lib PARENT_SCOPE)
 #---------------------------------------------------------------------
 # Define the install directory for elastix and transformix.
 
-if(NOT WIN32)
+if(ELASTIX_BUILD_EXECUTABLE AND NOT WIN32)
   # Tell the executables where to find the required .so files.
   set_target_properties(elastix_exe transformix_exe
     PROPERTIES INSTALL_RPATH "${CMAKE_INSTALL_PREFIX}/lib:${ITK_DIR}")
 endif()
 
-if(NOT ELASTIX_NO_INSTALL_EXECUTABLES)
+if(ELASTIX_BUILD_EXECUTABLE AND NOT ELASTIX_NO_INSTALL_EXECUTABLES)
   install(TARGETS elastix_exe transformix_exe
     ARCHIVE DESTINATION ${ELASTIX_ARCHIVE_DIR}
     LIBRARY DESTINATION ${ELASTIX_LIBRARY_DIR}

ElastixConfig.cmake.in

@@ -36,6 +36,7 @@ endif()
 
 
 # Set some variables that the user might want to use
+set( ELASTIX_BUILD_EXECUTABLE @ELASTIX_BUILD_EXECUTABLE@ )
 set( ELASTIX_USE_OPENMP @ELASTIX_USE_OPENMP@ )
 set( ELASTIX_USE_OPENCL @ELASTIX_USE_OPENCL@ )
 set( ELASTIX_USE_MEVISDICOMTIFF @ELASTIX_USE_MEVISDICOMTIFF@ )