FindOpenSceneGraph: Update documentation

- Extended examples section and changed example to use a locally created
  imported target showing how to add usage requirements to project.
- Mention of CMake 2.x removed as these version notes are now being
  cleaned in the CMake 4 documentation (CMake docs are at this point
  considering the 2.8.12.2 as the initial state upon which new and
  changed items are documented through versions).
- Extended components section.
- Added See Also section.
- Removed internal comment about naming conventions. Find modules
  distributed with CMake ideally should follow standard find modules
  naming conventions for variables and to have it synced with
  other find modules shipped with CMake.
- Used the OpenSceneGraph_FOUND variable (CMake 3.3). The uppercased
  OPENSCENEGRAPH_FOUND is also set to the same value.
- Added note in introduction how to include headers.

Modules/FindOpenSceneGraph.cmake

@@ -5,112 +5,256 @@
 FindOpenSceneGraph
 ------------------
 
-Find OpenSceneGraph (3D graphics application programming interface)
+Finds `OpenSceneGraph`_ (OSG), a 3D graphics application programming interface.
 
-This module searches for the OpenSceneGraph core "osg" library as well
-as :module:`FindOpenThreads`, and whatever additional ``COMPONENTS``
-(nodekits) that you specify.
+.. note::
 
-::
+  OpenSceneGraph development has largely transitioned to its successor project,
+  VulkanSceneGraph, which should be preferred for new code.  Refer to the
+  upstream documentation for guidance on using VulkanSceneGraph with CMake.
 
-    See http://www.openscenegraph.org
+This module searches for the OpenSceneGraph core osg library, its dependency
+OpenThreads, and additional OpenSceneGraph libraries, some of which are also
+known as *NodeKits*, if specified.
 
+When working with OpenSceneGraph, its core library headers are intended to be
+included in C++ project source code as:
 
+.. code-block:: c++
 
-NOTE: To use this module effectively you must either require ``CMake >=
-2.6.3`` with  :command:`cmake_minimum_required(VERSION 2.6.3)` or download
-and place :module:`FindOpenThreads`, :module:`Findosg` functions,
-:module:`Findosg` and ``Find<etc>.cmake`` files into your
-:variable:`CMAKE_MODULE_PATH`.
+  #include <osg/PositionAttitudeTransform>
 
-==================================
+Headers for the OpenSceneGraph libraries and NodeKits follow a similar inclusion
+structure, for example:
 
-This module accepts the following variables (note mixed case)
+.. code-block:: c++
 
-::
+  #include <osgAnimation/Animation>
+  #include <osgDB/DatabasePager>
+  #include <osgFX/BumpMapping>
+  // ...
 
-    OpenSceneGraph_DEBUG - Enable debugging output
+.. _`OpenSceneGraph`: https://openscenegraph.github.io/openscenegraph.io/
 
+Components
+^^^^^^^^^^
 
+OpenSceneGraph toolkit consists of the core library osg, and additional
+libraries, which can be optionally specified as components with the
+:command:`find_package` command:
 
-::
+.. code-block:: cmake
 
-    OpenSceneGraph_MARK_AS_ADVANCED - Mark cache variables as advanced
-                                      automatically
+  find_package(OpenSceneGraph [COMPONENTS <components>...])
 
+Supported components include:
 
+``osg``
+  Finds the core osg library (``libosg``), required to use OpenSceneGraph.
+  This component is always automatically implied.
 
-The following environment variables are also respected for finding the
-OSG and it's various components.  :variable:`CMAKE_PREFIX_PATH` can also be
-used for this (see :command:`find_library` CMake documentation).
+``OpenThreads``
+  Finds the dependent OpenThreads library (``libOpenThreads``) via the
+  :module:`FindOpenThreads` module.  This component is always automatically
+  implied as it is required to use OpenSceneGraph.
 
-``<MODULE>_DIR``
-  (where ``MODULE`` is of the form "OSGVOLUME" and there is
-  a :module:`FindosgVolume`.cmake` file)
-``OSG_DIR``
-  ..
-``OSGDIR``
-  ..
-``OSG_ROOT``
-  ..
+``osgAnimation``
+  Finds the osgAnimation library, which provides general purpose utility classes
+  for animation.
 
+``osgDB``
+  Finds the osgDB library for reading and writing scene graphs support.
 
-[CMake 2.8.10]: The CMake variable ``OSG_DIR`` can now be used as well to
-influence detection, instead of needing to specify an environment
-variable.
+``osgFX``
+  Finds the osgFX NodeKit, which provides a framework for implementing special
+  effects.
 
-This module defines the following output variables:
+``osgGA``
+  Finds the osgGA (GUI Abstraction) library, which provides facilities to work
+  with varying window systems.
 
-::
+``osgIntrospection``
+  Finds the osgIntrospection library, which provides a reflection framework for
+  accessing and invoking class properties and methods at runtime without
+  modifying the classes.
 
-    OPENSCENEGRAPH_FOUND - Was the OSG and all of the specified components found?
+  .. note::
+    The osgIntrospection library has been removed from the OpenSceneGraph
+    toolkit as of OpenSceneGraph version 3.0.
 
+``osgManipulator``
+  Finds the osgManipulator NodeKit, which provides support for 3D interactive
+  manipulators.
 
+``osgParticle``
+  Finds the osgParticle NodeKit, which provides support for particle effects.
 
-::
+``osgPresentation``
+  Finds the osgPresentation NodeKit, which provides support for 3D scene graph
+  based presentations.
 
-    OPENSCENEGRAPH_VERSION - The version of the OSG which was found
+  .. note::
+    This NodeKit has been added in OpenSceneGraph 3.0.0.
 
+``osgProducer``
+  Finds the osgProducer utility library, which provides functionality for window
+  management and event handling.
 
+  .. note::
+    The osgProducer has been removed from early versions of OpenSceneGraph
+    toolkit 1.x, and has been superseded by the osgViewer library.
 
-::
+``osgQt``
+  Finds the osgQt NodeKit, which provides various classes to aid the integration
+  of Qt.
 
-    OPENSCENEGRAPH_INCLUDE_DIRS - Where to find the headers
+  .. note::
+    As of OpenSceneGraph version 3.6, this NodeKit has been moved to its own
+    repository.
 
+``osgShadow``
+  Finds the osgShadow NodeKit, which provides support for a range of shadow
+  techniques.
 
+``osgSim``
+  Finds the osgSim NodeKit, which adds support for simulation features like
+  navigation lights and OpenFlight-style movement controls.
 
-::
+``osgTerrain``
+  Finds the osgTerrain NodeKit, which provides geospecifc terrain rendering
+  support.
 
-    OPENSCENEGRAPH_LIBRARIES - The OSG libraries
+``osgText``
+  Finds the osgText NodeKit, which provides high quality text support.
 
+``osgUtil``
+  Finds the osgUtil library, which provides general-purpose utilities like
+  update, cull, and draw traversals, as well as scene graph tools such as
+  optimization, triangle stripping, and tessellation.
 
+``osgViewer``
+  Finds the osgViewer library, which provides high level viewer functionality.
 
-================================== Example Usage:
+``osgVolume``
+  Finds the osgVolume NodeKit, which provides volume rendering support.
 
-.. code-block:: cmake
+``osgWidget``
+  Finds the osgWidget NodeKit, which provides support for 2D and 3D GUI widget
+  sets.
+
+If no components are specified, this module searches for the ``osg`` and
+``OpenThreads`` components by default.
+
+Result Variables
+^^^^^^^^^^^^^^^^
+
+This module defines the following variables:
+
+``OpenSceneGraph_FOUND``
+  Boolean indicating whether the (requested version of) OpenSceneGraph with all
+  specified components is found.  For backward compatibility, the
+  ``OPENSCENEGRAPH_FOUND`` variable is also set to the same value.
+
+``OPENSCENEGRAPH_VERSION``
+  The version of the OSG which was found.
+
+``OPENSCENEGRAPH_INCLUDE_DIRS``
+  Include directories containing headers needed to use OpenSceneGraph.
+
+``OPENSCENEGRAPH_LIBRARIES``
+  Libraries needed to link against to use OpenSceneGraph.
+
+Hints
+^^^^^
+
+This module accepts the following variables:
+
+``OpenSceneGraph_DEBUG``
+  Set this variable to boolean true to enable debugging output by this module.
 
-  find_package(OpenSceneGraph 2.0.0 REQUIRED osgDB osgUtil)
-      # libOpenThreads & libosg automatically searched
-  include_directories(${OPENSCENEGRAPH_INCLUDE_DIRS})
+``OpenSceneGraph_MARK_AS_ADVANCED``
+  Set this variable to boolean true to mark cache variables of this module as
+  advanced automatically.
 
+To help this module find OpenSceneGraph and its various components installed in
+custom location, :variable:`CMAKE_PREFIX_PATH` variable can be used.
+Additionally, the following variables are also respected:
 
+``<COMPONENT>_DIR``
+  Environment or CMake variable that can be set to the root of the OSG common
+  installation, where ``<COMPONENT>`` is the uppercase form of component listed
+  above.  For example, ``OSGVOLUME_DIR`` to find the ``osgVolume`` component.
+
+``OSG_DIR``
+  Environment or CMake variable that can be set to influence detection of
+  OpenSceneGraph installation root location as a whole.
+
+``OSGDIR``
+  Environment variable treated the same as ``OSG_DIR``.
+
+``OSG_ROOT``
+  Environment variable treated the same as ``OSG_DIR``.
+
+Examples
+^^^^^^^^
+
+Finding the OpenSceneGraph with ``osgDB`` and ``osgUtil`` libraries specified as
+components and creating an interface :ref:`imported target <Imported Targets>`
+that encapsulates its usage requirements for linking to a project target:
 
 .. code-block:: cmake
 
+  find_package(OpenSceneGraph 2.0.0 REQUIRED COMPONENTS osgDB osgUtil)
+
+  if(OpenSceneGraph_FOUND AND NOT TARGET OpenSceneGraph::OpenSceneGraph)
+    add_library(OpenSceneGraph::OpenSceneGraph INTERFACE IMPORTED)
+    set_target_properties(
+      OpenSceneGraph::OpenSceneGraph
+      PROPERTIES
+        INTERFACE_INCLUDE_DIRECTORIES "${OPENSCENEGRAPH_INCLUDE_DIRS}"
+        INTERFACE_LINK_LIBRARIES "${OPENSCENEGRAPH_LIBRARIES}"
+    )
+  endif()
+
   add_executable(foo foo.cc)
-  target_link_libraries(foo ${OPENSCENEGRAPH_LIBRARIES})
+
+  target_link_libraries(foo PRIVATE OpenSceneGraph::OpenSceneGraph)
+
+See Also
+^^^^^^^^
+
+The following OpenSceneGraph-related helper find modules are used internally by
+this module when finding specific OpenSceneGraph components.  These modules are
+not intended to be included or invoked directly by project code during typical
+use of ``find_package(OpenSceneGraph)``.  However, they can be useful for
+advanced scenarios where finer control over component detection is needed.  For
+example, to find them explicitly and override or bypass detection of specific
+OpenSceneGraph components:
+
+* The :module:`Findosg` module to find the core osg library.
+* The :module:`FindosgAnimation` module to find osgAnimation.
+* The :module:`FindosgDB` module to find osgDB.
+* The :module:`FindosgFX` module to find osgDB.
+* The :module:`FindosgGA` module to find osgGA.
+* The :module:`FindosgIntrospection` module to find osgIntrospection.
+* The :module:`FindosgManipulator` module to find osgManipulator.
+* The :module:`FindosgParticle` module to find osgParticle.
+* The :module:`FindosgPresentation` module to find osgPresentation.
+* The :module:`FindosgProducer` module to find osgProducer.
+* The :module:`FindosgQt` module to find osgQt.
+* The :module:`FindosgShadow` module to find osgShadow.
+* The :module:`FindosgSim` module to find osgSim.
+* The :module:`FindosgTerrain` module to find osgTerrain.
+* The :module:`FindosgText` module to find osgText.
+* The :module:`FindosgUtil` module to find osgUtil.
+* The :module:`FindosgViewer` module to find osgViewer.
+* The :module:`FindosgVolume` module to find osgVolume.
+* The :module:`FindosgWidget` module to find osgWidget.
 #]=======================================================================]
 
 cmake_policy(PUSH)
 cmake_policy(SET CMP0159 NEW) # file(STRINGS) with REGEX updates CMAKE_MATCH_<n>
 
-#
-# Naming convention:
-#  Local variables of the form _osg_foo
-#  Input variables of the form OpenSceneGraph_FOO
-#  Output variables of the form OPENSCENEGRAPH_FOO
-#
-
 include(${CMAKE_CURRENT_LIST_DIR}/Findosg_functions.cmake)
 
 set(_osg_modules_to_process)