VR: Find the osgXR library

Allow the osgXR[1] library to be found and linked against. We'll use
this to implement VR in FlightGear.

[1] https://github.com/amalon/osgXR

CMakeLists.txt

@@ -151,6 +151,11 @@ elseif(${CMAKE_SYSTEM_NAME} MATCHES "Linux" OR
     if(HTS_ENGINE_FOUND)
         set(SYSTEM_HTS_ENGINE_DEFAULT 1)
     endif()
+
+    find_package(osgXR 0.3)
+    if (osgXR_FOUND)
+        set(ENABLE_OSGXR_DEFAULT 1)
+    endif()
 endif()
 
 # FlightGear build options
@@ -171,6 +176,7 @@ option(SYSTEM_GSM        "Set to ON to build IAXClient with the system's GSM lib
 option(SYSTEM_FLITE      "Set to ON to build Flightgear with the system's Flite library" ${SYSTEM_FLITE_DEFAULT})
 option(SYSTEM_HTS_ENGINE "Set to ON to build Flightgear with the system's HTS Engine library" ${SYSTEM_HTS_ENGINE_DEFAULT})
 option(SYSTEM_CPPUNIT    "Set to ON to build Flightgear with the system's CppUnit library")
+option(ENABLE_OSGXR      "Set to ON to build Flightgear with OpenXR support via the osgXR library" ${ENABLE_OSGXR_DEFAULT})
 
 # additional utilities
 option(ENABLE_FGELEV     "Set to ON to build the fgelev application (default)" ON)

CMakeModules/SetupFGFSIncludes.cmake

@@ -4,6 +4,10 @@ function(setup_fgfs_includes target)
         target_include_directories(${target} PRIVATE ${PROJECT_SOURCE_DIR}/src/FDM/JSBSim)
     endif()
 
+    if(ENABLE_OSGXR)
+        target_include_directories(${target} PRIVATE ${osgXR_INCLUDE_DIR})
+    endif()
+
     target_include_directories(${target} PRIVATE ${PLIB_INCLUDE_DIR})
     target_include_directories(${target} PRIVATE ${PROJECT_SOURCE_DIR}/3rdparty/cjson)
     # only actually needed for httpd.cxx

CMakeModules/SetupFGFSLibraries.cmake

@@ -23,6 +23,10 @@ function(setup_fgfs_libraries target)
         target_link_libraries(${target} ${X11_LIBRARIES})
     endif()
 
+    if(ENABLE_OSGXR)
+        target_link_libraries(${target} osgXR::osgXR)
+    endif()
+
     target_link_libraries(${target} fgsqlite3 fgvoicesynth fgembeddedresources)
 
     target_link_libraries(${target}

src/Include/config_cmake.h.in

@@ -75,3 +75,5 @@
 
 #cmakedefine HAVE_SENTRY
 #define SENTRY_API_KEY "@sentry_api_key@"
+
+#cmakedefine ENABLE_OSGXR