Change so that different flavours of VTK might be chosen by the user. See full instructions in that file.

Modules/FindVTK.cmake

@@ -1,83 +1,140 @@
 #
 # Find the native VTK includes and library
 #
-# This module defines
+# This module defines:
 #
-# VTK_INSTALL_PATH - where is the installed version of VTK
-# VTK_BINARY_PATH - where is the binary tree (only defined if SOURCE_PATH is defined)
-# USE_INSTALLED_VTK - sould an installed or source version of VTK be used
-# USE_VTK_FILE - the full path and location of the UseVTK.cmake file
+# VTK_INSTALL_PATH  - where is the installed version of VTK.
+# USE_BUILT_VTK     - should a built-from-source version of VTK be used
+#
+# VTK_BINARY_PATH   - where is (one of) the binary tree(s).
+# USE_INSTALLED_VTK - should an installed version of VTK be used
+#
+# USE_VTK_FILE      - the full path and location of the UseVTK.cmake file
+#                     ONLY SET if ONE of the USE_BUILT_VTK or 
+#                     USE_INSTALLED_VTK is set to ON.
 #
 
 #
-# Look for a binary tree
+# Look for a binary tree (built from source)
 # 
 FIND_PATH(VTK_BINARY_PATH UseVTK.cmake
-    [HKEY_CURRENT_USER\\Software\\Kitware\\CMakeSetup\\Settings\\StartPath;WhereBuild1]
-    [HKEY_CURRENT_USER\\Software\\Kitware\\CMakeSetup\\Settings\\StartPath;WhereBuild2]
-    [HKEY_CURRENT_USER\\Software\\Kitware\\CMakeSetup\\Settings\\StartPath;WhereBuild3]
-    [HKEY_CURRENT_USER\\Software\\Kitware\\CMakeSetup\\Settings\\StartPath;WhereBuild4]
-    [HKEY_CURRENT_USER\\Software\\Kitware\\CMakeSetup\\Settings\\StartPath;WhereBuild5]
-    [HKEY_CURRENT_USER\\Software\\Kitware\\CMakeSetup\\Settings\\StartPath;WhereBuild6]
-    [HKEY_CURRENT_USER\\Software\\Kitware\\CMakeSetup\\Settings\\StartPath;WhereBuild7]
-    [HKEY_CURRENT_USER\\Software\\Kitware\\CMakeSetup\\Settings\\StartPath;WhereBuild8]
-    [HKEY_CURRENT_USER\\Software\\Kitware\\CMakeSetup\\Settings\\StartPath;WhereBuild9]
-    [HKEY_CURRENT_USER\\Software\\Kitware\\CMakeSetup\\Settings\\StartPath;WhereBuild10]
-    ../VTKBIN
-    ../vtkbin
-    VTKBIN
-    vtkbin
-    $ENV{HOME}/VTKBIN
-    $ENV{HOME}/vtkbin
-    )
+  [HKEY_CURRENT_USER\\Software\\Kitware\\CMakeSetup\\Settings\\StartPath;WhereBuild1]
+  [HKEY_CURRENT_USER\\Software\\Kitware\\CMakeSetup\\Settings\\StartPath;WhereBuild2]
+  [HKEY_CURRENT_USER\\Software\\Kitware\\CMakeSetup\\Settings\\StartPath;WhereBuild3]
+  [HKEY_CURRENT_USER\\Software\\Kitware\\CMakeSetup\\Settings\\StartPath;WhereBuild4]
+  [HKEY_CURRENT_USER\\Software\\Kitware\\CMakeSetup\\Settings\\StartPath;WhereBuild5]
+  [HKEY_CURRENT_USER\\Software\\Kitware\\CMakeSetup\\Settings\\StartPath;WhereBuild6]
+  [HKEY_CURRENT_USER\\Software\\Kitware\\CMakeSetup\\Settings\\StartPath;WhereBuild7]
+  [HKEY_CURRENT_USER\\Software\\Kitware\\CMakeSetup\\Settings\\StartPath;WhereBuild8]
+  [HKEY_CURRENT_USER\\Software\\Kitware\\CMakeSetup\\Settings\\StartPath;WhereBuild9]
+  [HKEY_CURRENT_USER\\Software\\Kitware\\CMakeSetup\\Settings\\StartPath;WhereBuild10]
+  ../VTKBIN
+  ../vtkbin
+  VTKBIN
+  vtkbin
+  $ENV{HOME}/VTKBIN
+  $ENV{HOME}/vtkbin
+)
+
+#
+# Look for an installed tree
+#
+FIND_PATH(VTK_INSTALL_PATH include/vtk/UseVTK.cmake
+  /usr/local
+  /usr
+  [HKEY_LOCAL_MACHINE\\SOFTWARE\\Kitware\\VTK\\Nightly]
+  [HKEY_LOCAL_MACHINE\\SOFTWARE\\Kitware\\VTK\\43]
+  [HKEY_LOCAL_MACHINE\\SOFTWARE\\Kitware\\VTK\\42]
+  [HKEY_LOCAL_MACHINE\\SOFTWARE\\Kitware\\VTK\\41]
+  [HKEY_LOCAL_MACHINE\\SOFTWARE\\Kitware\\VTK\\40]
+)
 
 #
-# If we found a binary tree then set use_installed_vtk to 0
+# If we found a built tree, USE_BUILT_VTK allows the user to 
+# use it or not.
+#
+# Important: it *has* to be set to OFF first in order to allow
+# the user to change the VTK_BINARY_PATH value *before* the USE_VTK_FILE
+# is set (and the cache created). 
+#
+# For example, CMake could have picked-up the wrong VTK binary path, and if 
+# the related VTK cache was immediately loaded there would not be any way
+# to overwrite these cache values (even by changing the binary path or
+# USE_VTK_FILE).
 #
 IF (VTK_BINARY_PATH)
-  SET (USE_INSTALLED_VTK 0 CACHE BOOL "Is an installed (versus source) version of VTK used")
-ELSE (VTK_BINARY_PATH)
-  # look for installed path
-  FIND_PATH(VTK_INSTALL_PATH include/vtk/UseVTK.cmake
-    /usr/local
-    /usr
-    [HKEY_LOCAL_MACHINE\\SOFTWARE\\Kitware\\VTK\\Nightly]
-    [HKEY_LOCAL_MACHINE\\SOFTWARE\\Kitware\\VTK\\43]
-    [HKEY_LOCAL_MACHINE\\SOFTWARE\\Kitware\\VTK\\42]
-    [HKEY_LOCAL_MACHINE\\SOFTWARE\\Kitware\\VTK\\41]
-    [HKEY_LOCAL_MACHINE\\SOFTWARE\\Kitware\\VTK\\40]
-    )
-  IF (VTK_INSTALL_PATH)
-    SET (USE_INSTALLED_VTK 1 CACHE BOOL "Is an installed (versus source) version of VTK used")
-  ENDIF (VTK_INSTALL_PATH)
+  SET (USE_BUILT_VTK 0 CACHE BOOL 
+       "Use a built (versus installed) version of VTK. Be sure VTK_BINARY_PATH is correct before setting it to ON.")
 ENDIF (VTK_BINARY_PATH)
 
-IF (USE_INSTALLED_VTK)
-  # look for the vtk header files in installed places
-  FIND_PATH(VTK_INSTALL_PATH include/vtk/UseVTK.cmake
-    /usr/local
-    /usr
-    [HKEY_LOCAL_MACHINE\\SOFTWARE\\Kitware\\VTK\\Nightly]
-    [HKEY_LOCAL_MACHINE\\SOFTWARE\\Kitware\\VTK\\43]
-    [HKEY_LOCAL_MACHINE\\SOFTWARE\\Kitware\\VTK\\42]
-    [HKEY_LOCAL_MACHINE\\SOFTWARE\\Kitware\\VTK\\41]
-    [HKEY_LOCAL_MACHINE\\SOFTWARE\\Kitware\\VTK\\40]
-    )
-  IF (VTK_INSTALL_PATH)
-    SET (USE_INSTALLED_VTK 1 CACHE BOOL "Is an installed (versus source) version of VTK used")
-  ENDIF (VTK_INSTALL_PATH)
-ENDIF (USE_INSTALLED_VTK)
-
+#
+# If we found an installed tree, USE_INSTALLED_VTK allows the user to 
+# use it or not.
+#
+# Important: it *has* to be set to OFF first in order to allow
+# the user to change the VTK_INSTALL_PATH value before the USE_VTK_FILE
+# is set (and the cache created).
+#
+# For example, you might have simultaneously installed different major
+# versions like VTK 3.2, 4.0, 5.1, etc.
+#
+# Moreover, USE_INSTALLED_VTK has to be OFF since USE_BUILT_VTK has to be OFF
+# too (see above). If USE_INSTALLED_VTK was ON by default, then USE_VTK_FILE
+# would be set immediately (since one of them is ON) in favor of the 
+# installed tree.
+#
+IF (VTK_INSTALL_PATH)
+  SET (USE_INSTALLED_VTK 0 CACHE BOOL 
+       "Use an installed (versus built from source) version of VTK. Be sure VTK_INSTALL_PATH is correct before setting it to ON.")
+ENDIF (VTK_INSTALL_PATH)
 
-IF (USE_INSTALLED_VTK)
-  IF (VTK_INSTALL_PATH)
-    SET (USE_VTK_FILE ${VTK_INSTALL_PATH}/include/vtk/UseVTK.cmake)
-  ENDIF (VTK_INSTALL_PATH)
-ELSE (USE_INSTALLED_VTK)
-  IF (VTK_BINARY_PATH)
+#
+# Set the USE_VTK_FILE only if one of USE_BUILT_VTK or USE_INSTALLED_VTK
+# is ON, i.e. if the user has decided if he wants to use either the built
+# or the installed VTK. Even if only one of the VTK flavor was found,
+# this also enable the user to change the path to his VTK (in case the
+# wrong installed or built VTK was automatically found).
+#
+# Once this decision has been made, there is no way to go back except by
+# erasing the cache. Mark these useless vars as ADVANCED to reflect this.
+#
+IF (USE_BUILT_VTK)
+  IF (NOT USE_INSTALLED_VTK)
     FIND_FILE(USE_VTK_FILE UseVTK.cmake ${VTK_BINARY_PATH})
-  ENDIF (VTK_BINARY_PATH)
-ENDIF (USE_INSTALLED_VTK)
-
-
+    MARK_AS_ADVANCED(
+      USE_BUILT_VTK
+      USE_INSTALLED_VTK
+      USE_VTK_FILE 
+      VTK_INSTALL_PATH
+    )
+  ENDIF (NOT USE_INSTALLED_VTK)
+ELSE (USE_BUILT_VTK)
+  IF (USE_INSTALLED_VTK)
+    SET (USE_VTK_FILE ${VTK_INSTALL_PATH}/include/vtk/UseVTK.cmake)
+    MARK_AS_ADVANCED(
+      USE_BUILT_VTK
+      USE_INSTALLED_VTK
+      USE_VTK_FILE 
+      VTK_BINARY_PATH
+    )
+  ENDIF (USE_INSTALLED_VTK)
+ENDIF (USE_BUILT_VTK)
 
+# Note:
+#
+# If you use that module then you are probably relying on VTK to be found
+# on your system. As said before, it might be found as different flavours: 
+# installed VTK, or (multiple) built VTK. Moreover, even if it is found
+# automatically, CMake might have picked the wrong path/version.
+#
+# Here is the CMake code you might probably want to use to work hand-in-hand
+# with that module:
+#
+# INCLUDE (${CMAKE_ROOT}/Modules/FindVTK.cmake)
+#
+# IF (USE_VTK_FILE)
+#   INCLUDE (${USE_VTK_FILE})
+# ELSE (USE_VTK_FILE)
+#   MESSAGE("Warning. This project is supposed to work with VTK, which might be found on your system as different flavours: installed VTK, or (multiple) built VTK. Please, make sure that the VTK_INSTALL_PATH or VTK_BINARY_PATH setting reflect which VTK you are planning to use, then set one of the USE_INSTALLED_VTK or USE_BUILT_VTK to ON.")
+#   SET (CAN_BUILD 0)
+# ENDIF (USE_VTK_FILE)