Modernize FindVTK module

This teaches the FindVTK module to use the Config mode of find_package()
to search for VTKConfig in the common case.  The old search method based
on find_path() and UseVTK is now used only to search for VTK 4.0.

This approach avoids the need to update the module for each new VTK
version because find_package(VTK) automatically searches "lib/vtk*".  It
also addresses issue #9105 since find_package searches lib64 paths too.

Modules/FindVTK.cmake

@@ -40,32 +40,41 @@
 # (To distributed this file outside of CMake, substitute the full
 #  License text for the above reference.)
 
+# Assume not found.
+SET(VTK_FOUND 0)
+
+# VTK 4.0 did not provide VTKConfig.cmake.
+IF("${VTK_FIND_VERSION}" VERSION_LESS 4.1)
+  SET(_VTK_40_ALLOW 1)
+  IF(VTK_FIND_VERSION)
+    SET(_VTK_40_ONLY 1)
+  ENDIF()
+ENDIF()
+
 # Construct consitent error messages for use below.
-SET(VTK_DIR_DESCRIPTION "directory containing VTKConfig.cmake.  This is either the root of the build tree, or PREFIX/lib/vtk for an installation.  For VTK 4.0, this is the location of UseVTK.cmake.  This is either the root of the build tree or PREFIX/include/vtk for an installation.")
+SET(VTK_DIR_DESCRIPTION "directory containing VTKConfig.cmake.  This is either the root of the build tree, or PREFIX/lib/vtk for an installation.")
+IF(_VTK_40_ALLOW)
+  SET(VTK_DIR_DESCRIPTION "${VTK_DIR_DESCRIPTION}  For VTK 4.0, this is the location of UseVTK.cmake.  This is either the root of the build tree or PREFIX/include/vtk for an installation.")
+ENDIF()
 SET(VTK_DIR_MESSAGE "VTK not found.  Set the VTK_DIR cmake cache entry to the ${VTK_DIR_DESCRIPTION}")
 
-# Search only if the location is not already known.
-IF(NOT VTK_DIR)
-  # Get the system search path as a list.
-  IF(UNIX)
-    STRING(REGEX MATCHALL "[^:]+" VTK_DIR_SEARCH1 "$ENV{PATH}")
-  ELSE(UNIX)
-    STRING(REGEX REPLACE "\\\\" "/" VTK_DIR_SEARCH1 "$ENV{PATH}")
-  ENDIF(UNIX)
-  STRING(REGEX REPLACE "/;" ";" VTK_DIR_SEARCH2 "${VTK_DIR_SEARCH1}")
+# Check whether VTK 4.0 has already been found.
+IF(_VTK_40_ALLOW AND VTK_DIR)
+  IF(EXISTS ${VTK_DIR}/UseVTK.cmake AND NOT EXISTS ${VTK_DIR}/VTKConfig.cmake)
+    SET(VTK_FOUND 1)
+    INCLUDE(UseVTKConfig40) # No VTKConfig; load VTK 4.0 settings.
+  ENDIF()
+ENDIF()
 
-  # Construct a set of paths relative to the system search path.
-  SET(VTK_DIR_SEARCH "")
-  FOREACH(dir ${VTK_DIR_SEARCH2})
-    SET(VTK_DIR_SEARCH ${VTK_DIR_SEARCH}
-      ${dir}/../lib/vtk-5.4
-      ${dir}/../lib/vtk-5.2
-      ${dir}/../lib/vtk-5.1
-      ${dir}/../lib/vtk-5.0
-      ${dir}/../lib/vtk
-      )
-  ENDFOREACH(dir)
+# Use the Config mode of the find_package() command to find VTKConfig.
+# If this succeeds (possibly because VTK_DIR is already set), the
+# command will have already loaded VTKConfig.cmake and set VTK_FOUND.
+IF(NOT _VTK_40_ONLY AND NOT VTK_FOUND)
+  FIND_PACKAGE(VTK QUIET NO_MODULE)
+ENDIF()
 
+# Special search for VTK 4.0.
+IF(_VTK_40_ALLOW AND NOT VTK_DIR)
   # Old scripts may set these directories in the CMakeCache.txt file.
   # They can tell us where to find VTKConfig.cmake.
   SET(VTK_DIR_SEARCH_LEGACY "")
@@ -77,22 +86,16 @@ IF(NOT VTK_DIR)
         ${VTK_INSTALL_PATH}/lib/vtk)
   ENDIF(VTK_INSTALL_PATH AND USE_INSTALLED_VTK)
 
-  #
-  # Look for an installation or build tree.
-  #
-  FIND_PATH(VTK_DIR UseVTK.cmake
-    # Support legacy cache files.
-    ${VTK_DIR_SEARCH_LEGACY}
-
-    # Look for an environment variable VTK_DIR.
-    $ENV{VTK_DIR}
+  # Look for UseVTK.cmake in build trees or under <prefix>/include/vtk.
+  FIND_PATH(VTK_DIR
+    NAMES UseVTK.cmake
+    PATH_SUFFIXES vtk-4.0 vtk
+    HINTS $ENV{VTK_DIR}
 
-    # Look in places relative to the system executable search path.
-    ${VTK_DIR_SEARCH}
+    PATHS
 
-    # Look in standard UNIX install locations.
-    /usr/local/lib/vtk
-    /usr/lib/vtk
+    # Support legacy cache files.
+    ${VTK_DIR_SEARCH_LEGACY}
 
     # Read from the CMakeSetup registry entries.  It is likely that
     # VTK will have been recently built.
@@ -109,34 +112,18 @@ IF(NOT VTK_DIR)
 
     # Help the user find it if we cannot.
     DOC "The ${VTK_DIR_DESCRIPTION}"
-  )
-ENDIF(NOT VTK_DIR)
-
-# If VTK was found, load the configuration file to get the rest of the
-# settings.
-IF(VTK_DIR)
-  # Make sure the VTKConfig.cmake file exists in the directory provided.
-  IF(EXISTS ${VTK_DIR}/VTKConfig.cmake)
-
-    # We found VTK.  Load the settings.
-    SET(VTK_FOUND 1)
-    INCLUDE(${VTK_DIR}/VTKConfig.cmake)
+    )
 
-  ELSE(EXISTS ${VTK_DIR}/VTKConfig.cmake)
-    IF(EXISTS ${VTK_DIR}/UseVTK.cmake)
-      # We found VTK 4.0 (UseVTK.cmake exists, but not VTKConfig.cmake).
+  IF(VTK_DIR)
+    IF(EXISTS ${VTK_DIR}/UseVTK.cmake AND NOT EXISTS ${VTK_DIR}/VTKConfig.cmake)
       SET(VTK_FOUND 1)
-      # Load settings for VTK 4.0.
-      INCLUDE(UseVTKConfig40)
-    ELSE(EXISTS ${VTK_DIR}/UseVTK.cmake)
-      # We did not find VTK.
-      SET(VTK_FOUND 0)
-    ENDIF(EXISTS ${VTK_DIR}/UseVTK.cmake)
-  ENDIF(EXISTS ${VTK_DIR}/VTKConfig.cmake)
-ELSE(VTK_DIR)
-  # We did not find VTK.
-  SET(VTK_FOUND 0)
-ENDIF(VTK_DIR)
+      INCLUDE(UseVTKConfig40) # No VTKConfig; load VTK 4.0 settings.
+    ELSE()
+      # We found the wrong version.  Pretend we did not find it.
+      SET(VTK_DIR "VTK_DIR-NOTFOUND" CACHE PATH "The ${VTK_DIR_DESCRIPTION}" FORCE)
+    ENDIF()
+  ENDIF()
+ENDIF()
 
 #-----------------------------------------------------------------------------
 IF(VTK_FOUND)