From 595c8a2fcb51a36b28bc2cfb97c9a85168775b19 Mon Sep 17 00:00:00 2001
From: James Hogan <james@albanarts.com>
Date: Wed, 12 Jan 2022 23:25:15 +0000
Subject: [PATCH] CMake: Fallback to built-in osgXR library

Fall back to using the new built-in osgXR library in 3rdparty/ if no
system library is provided and OpenXR is available.
---
 3rdparty/CMakeLists.txt               |  4 ++++
 CMakeLists.txt                        | 26 +++++++++++++++++++++-----
 CMakeModules/SetupFGFSLibraries.cmake |  4 ++--
 3 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/3rdparty/CMakeLists.txt b/3rdparty/CMakeLists.txt
index de17e1eec..2e7b90a23 100644
--- a/3rdparty/CMakeLists.txt
+++ b/3rdparty/CMakeLists.txt
@@ -29,3 +29,7 @@ endif()
 if (NOT SYSTEM_CPPUNIT)
     add_subdirectory(cppunit)
 endif()
+
+if (ENABLE_OSGXR AND NOT ENABLE_SYSTEM_OSGXR)
+    add_subdirectory(osgXR)
+endif()
diff --git a/CMakeLists.txt b/CMakeLists.txt
index cb1705088..9d8e8153b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -155,6 +155,13 @@ elseif(${CMAKE_SYSTEM_NAME} MATCHES "Linux" OR
     endif()
 endif()
 
+if (ENABLE_VR_DEFAULT)
+    find_package(osgXR 0.3.3 QUIET)
+    if (osgXR_FOUND)
+        set(SYSTEM_OSGXR_DEFAULT 1)
+    endif()
+endif()
+
 # FlightGear build options
 option(LOGGING           "Set to ON to build FlightGear with logging support (default)" ON)
 option(JSBSIM_TERRAIN    "Set to ON to build FlightGear with JSBSim terrain handling code" ON)
@@ -169,6 +176,7 @@ option(SYSTEM_SQLITE     "Set to ON to build FlightGear with the system's SQLite
 option(ENABLE_IAX        "Set to ON to build FlightGear with IAXClient/fgcom built-in (default)" ON)
 option(USE_DBUS          "Set to ON to build FlightGear with DBus screensaver interaction (default on Linux)" ${USE_DBUS_DEFAULT})
 option(ENABLE_VR         "Set to ON to build Flightgear with VR support" ${ENABLE_VR_DEFAULT})
+option(SYSTEM_OSGXR      "Set to ON to build Flightgear with the system's osgXR library" ${SYSTEM_OSGXR_DEFAULT})
 option(SYSTEM_SPEEX      "Set to ON to build IAXClient with the system's speex and speexdsp library" ${SYSTEM_SPEEX_DEFAULT})
 option(SYSTEM_GSM        "Set to ON to build IAXClient with the system's GSM library" ${SYSTEM_GSM_DEFAULT})
 option(SYSTEM_FLITE      "Set to ON to build Flightgear with the system's Flite library" ${SYSTEM_FLITE_DEFAULT})
@@ -301,13 +309,21 @@ endif (USE_DBUS)
 ##############################################################################
 ## VR setup
 if (ENABLE_VR)
-    find_package(osgXR 0.3.3 QUIET)
-    if (osgXR_FOUND)
-        message(STATUS "VR support enabled")
+    if (SYSTEM_OSGXR AND osgXR_FOUND)
+        message(STATUS "VR support enabled, using system osgXR library")
+        add_library(osgXR ALIAS osgXR::osgXR)
         set(ENABLE_OSGXR 1)
+        set(ENABLE_SYSTEM_OSGXR 1)
     else()
-        message(STATUS "VR support disabled, compatible osgXR library not found")
-        set(ENABLE_OSGXR 0)
+        find_package(OpenXR QUIET)
+        if (OpenXR_FOUND)
+            message(STATUS "VR support enabled, using built-in osgXR library")
+            set(ENABLE_OSGXR 1)
+            set(ENABLE_SYSTEM_OSGXR 0)
+        else()
+            message(STATUS "VR support disabled, OpenXR not found")
+            set(ENABLE_OSGXR 0)
+        endif()
     endif()
 else()
     message(STATUS "VR support disabled")
diff --git a/CMakeModules/SetupFGFSLibraries.cmake b/CMakeModules/SetupFGFSLibraries.cmake
index 8e69b8801..13344ec4f 100644
--- a/CMakeModules/SetupFGFSLibraries.cmake
+++ b/CMakeModules/SetupFGFSLibraries.cmake
@@ -24,7 +24,7 @@ function(setup_fgfs_libraries target)
     endif()
 
     if(ENABLE_OSGXR)
-        target_link_libraries(${target} osgXR::osgXR)
+        target_link_libraries(${target} osgXR)
     endif()
 
     target_link_libraries(${target} fgsqlite3 fgvoicesynth fgembeddedresources)
@@ -118,7 +118,7 @@ function (setup_fgfs_library_includes target)
     endif()    
     
     if(ENABLE_OSGXR)
-        _apply_target_includes(${target} osgXR::osgXR)
+        _apply_target_includes(${target} osgXR)
     endif()
 
     _apply_target_includes(${target} fgsqlite3)