Why is Linux support disabled in the XR gems?

[ChristophHaag]

I'm not familiar with o3de, but wanted to see if the XR support worked on Linux. So I installed the 24.09.0 binary version of o3de on archlinux

Creating a new project with the downloaded XR gems from the asset library predictably didn't launch any XR mode when going into play mode with ctrl+g, so I deleted the downloaded gems in the Gem directory and tried to add the ones from an o3de-extras checkout of the 2409.0 branch but other than outputting 1.12.1 these commands do nothing:

$ /opt/O3DE/24.09/scripts/o3de.sh register -gp /home/haagch/o3de-extras/Gems/XR -espp /home/haagch/O3DE/Projects/OpenXRTest/1.0.1
1.12.1
$ /opt/O3DE/24.09/scripts/o3de.sh register -gp /home/haagch/o3de-extras/Gems/OpenXRVk -espp /home/haagch/O3DE/Projects/OpenXRTest/1.0.1
1.12.1 

so I just went ahead and added them manually in my project in project.json

    "external_subdirectories": [
        "Gem",
        "/home/haagch/o3de-extras/Gems/XR",
        "/home/haagch/o3de-extras/Gems/OpenXRVk"
    ],

Now to the gem code.

First I see this commit but I could not find any rationale to why: 6001b28

Once I revert that commit and click build in the editor, it hits this error #error "Linux Window Manager not recognized." https://github.com/o3de/o3de-extras/blob/2409.0/Gems/OpenXRVk/Code/Include/OpenXRVk/Platform/Linux/OpenXRVk_Linux.h#L17-L24

afaik you only support OpenXR with the Vulkan RHI, which has no need for any interaction with xlib/xcb or wayland (the wayland graphics binding really shouldn't exist in this form anyway). So once I delete these ifdefs and hit build again, I am hit with a less clear linking error

[1/13] Linking CXX static library lib/profile/libXR.Static.a
[2/13] Copying XR runtime dependencies to output...
[3/13] Building CXX object External/XR-d0652409/Code/CMakeFiles/XR.dir/profile/Unity/unity_0_cxx.cxx.o
[4/13] Linking CXX shared module bin/profile/libXR.so
FAILED: bin/profile/libXR.so 
: && /usr/sbin/clang++ -fPIC -fno-exceptions -fvisibility=hidden -fvisibility-inlines-hidden -Wall -Werror -Wno-inconsistent-missing-override -Wrange-loop-analysis -Wno-unknown-warning-option -Wno-parentheses -Wno-reorder -Wno-switch -Wno-undefined-var-template -msse4.1  -O2 -g -fstack-protector-all -fstack-check  -Wl,--no-undefined -fpie -Wl,-z,relro,-z,now -Wl,-z,noexecstack -shared  -o bin/profile/libXR.so External/XR-d0652409/Code/CMakeFiles/XR.dir/profile/Unity/unity_0_cxx.cxx.o  -Wl,-rpath,"\$ORIGIN"  lib/profile/libXR.Static.a  /opt/O3DE/24.09/lib/Linux/profile/Default/libAtom_RPI.Public.a  /opt/O3DE/24.09/lib/Linux/profile/Default/libAtom_RHI.Public.a  /opt/O3DE/24.09/lib/Linux/profile/Default/libAtom_RHI.Reflect.a  /opt/O3DE/24.09/lib/Linux/profile/Default/libAzFramework.a  /opt/O3DE/24.09/lib/Linux/profile/Default/libAzNetworking.a  /home/haagch/.o3de/3rdParty/packages/OpenSSL-1.1.1t-rev1-linux/OpenSSL/lib/libssl.a  /home/haagch/.o3de/3rdParty/packages/OpenSSL-1.1.1t-rev1-linux/OpenSSL/lib/libcrypto.a  /home/haagch/.o3de/3rdParty/packages/lz4-1.9.4-rev2-linux/lz4/lib/liblz4.a  /opt/O3DE/24.09/lib/Linux/profile/Default/libAtomCore.a  /opt/O3DE/24.09/lib/Linux/profile/Default/libAzCore.a  /home/haagch/.o3de/3rdParty/packages/Lua-5.4.4-rev1-linux/Lua/lib/release/liblualib.a  /home/haagch/.o3de/3rdParty/packages/zlib-1.2.11-rev5-linux/zlib/lib/libz.a  /usr/lib/libzstd.so  /home/haagch/.o3de/3rdParty/packages/cityhash-1.1-multiplatform/cityhash/build/linux/clang-3.8/release/libcityhash.a  /opt/O3DE/24.09/bin/Linux/profile/Default/./libO3DEKernel.so  -ldl  -lpthread  /usr/lib/libunwind.so  -latomic && cd /home/haagch/O3DE/Projects/openxrtest/build/linux/External/XR-d0652409/Code && /usr/bin/cmake -P /opt/O3DE/24.09/cmake/Platform/Linux/ProcessDebugSymbols.cmake /usr/bin/strip /usr/bin/objcopy /home/haagch/O3DE/Projects/openxrtest/build/linux/bin/profile/libXR.so dbg MODULE_LIBRARY DETACH
/usr/sbin/ld: lib/profile/libXR.Static.a(unity_0_cxx.cxx.o): in function `AZ::AzTypeInfo<AZStd::basic_fixed_string<char, 256ul, AZStd::char_traits<char> > >::GetCanonicalTypeId()':
/opt/O3DE/24.09/Code/Framework/AzCore/./AzCore/RTTI/TypeInfoSimple.h:317:(.text.startup[_ZN2XR39r_default_openxr_foveated_pass_templateE]+0x144): undefined reference to `_ZN5AZStd13GetO3deTypeIdIcTnDaLm256ENS_11char_traitsIcEEEEN2AZ4UuidENS3_3AdlENS_13type_identityINS_18basic_fixed_stringIT_XT0_ET1_EEEE'

might this be because of differences in the debian build and clang 18.1.8 from archlinux?

[byrcolin]

@ChristophHaag It appears you are doing a few things slightly incorrectly.
First, the registration commands should add a line to the /.o3de/o3de_manifest.json. Then in your projects and gems that refer to these objects should only use the name of the object.
Second: "external_subdirectories": [
"Gem",
"/home/haagch/o3de-extras/Gems/XR",
"/home/haagch/o3de-extras/Gems/OpenXRVk"
],
This is a list of sub directories that will be descended by cmake. If you want to include the object you would add the name of he object to the project.json, not the path into the gem_names I think...
The TRAIT being set to FALSE is something I'll have to look into... not sure why off the top of my head that is.
Also I would use the project manager to do all this. It does just call the underlying CLI commands but does it all for you so less chance of a making these kind of mistakes.

I'm going to call this a feature request and accept triage on it as I want to loo into why the TRAIT was set to false. Once I can determine that I will update this issue and close it.