Add Qt5 support for VTK.

Only VTK >= 6 is supported.

CMakeExternals/VTK.cmake

@@ -54,6 +54,19 @@ if(NOT DEFINED VTK_DIR AND NOT ${CMAKE_PROJECT_NAME}_USE_SYSTEM_${proj})
       )
   endif()
 
+  if(CTK_QT_VERSION VERSION_LESS "5")
+    list(APPEND additional_vtk_cmakevars
+      -DVTK_QT_VERSION:STRING=4
+      -DDESIRED_QT_VERSION:STRING=4
+      )
+  else()
+    list(APPEND additional_vtk_cmakevars
+      -DVTK_QT_VERSION:STRING=5
+      -DDESIRED_QT_VERSION:STRING=5
+      -DCMAKE_PREFIX_PATH:STRING=${CMAKE_PREFIX_PATH}
+      )
+  endif()
+
   ExternalProject_Add(${proj}
     ${${proj}_EXTERNAL_PROJECT_ARGS}
     SOURCE_DIR ${CMAKE_BINARY_DIR}/${proj}
@@ -69,10 +82,10 @@ if(NOT DEFINED VTK_DIR AND NOT ${CMAKE_PROJECT_NAME}_USE_SYSTEM_${proj})
       -DVTK_WRAP_PYTHON:BOOL=${CTK_LIB_Scripting/Python/Core_PYTHONQT_USE_VTK}
       -DVTK_WRAP_JAVA:BOOL=OFF
       -DBUILD_SHARED_LIBS:BOOL=ON
-      -DDESIRED_QT_VERSION:STRING=4
       -DVTK_USE_GUISUPPORT:BOOL=ON
       -DVTK_USE_QVTK_QTOPENGL:BOOL=ON
-      -DVTK_USE_QT:BOOL=ON
+      -DVTK_USE_QT:BOOL=ON # VTK 5
+      -DVTK_Group_Qt:BOOL=ON # VTK 6
       -DVTK_LEGACY_REMOVE:BOOL=ON
       -DQT_QMAKE_EXECUTABLE:FILEPATH=${QT_QMAKE_EXECUTABLE}
     DEPENDS

CMakeLists.txt

@@ -502,13 +502,11 @@ ctk_lib_option(Scripting/Python/Widgets
                "Build the Python Widgets library" OFF)
 
 # VTK libraries have not yet been tested with Qt5
-if(CTK_QT_VERSION VERSION_LESS "5")
 ctk_lib_option(Visualization/VTK/Core
                "Build the VTK Core library" OFF)
 
 ctk_lib_option(Visualization/VTK/Widgets
                "Build the VTK Widgets library" OFF)
-endif()
 
 ctk_lib_option(CommandLineModules/Core
                "Build the Command Line Module core library" OFF)