OpenXR SDK does not compile on Windows without `XR_USE_GRAPHICS_API_D3D11`/similar

Hi there! This is a fairly minor issue, but it caused me a little grief recently. I’ve been integrating the SDK into a non-DX codebase using a different build system and used a minimal set of defines to add Windows support:

'API_NAME="OpenXR"',
"XR_USE_TIMESPEC",
"XR_CURRENT_API_MAJOR_VERSION=1",
"XR_CURRENT_API_MINOR_VERSION=0",
"XR_CURRENT_API_PATCH_VERSION=13",
"XR_USE_GRAPHICS_API_OPENGL",
"XR_USE_PLATFORM_WIN32", 
"XR_OS_WINDOWS", 
"WIN32", 
"_WINDOWS", 

However, this will not compile. openxr/openxr_platform.h refers to IUnknown, which isn’t pulled in by xr_dependencies.h with the above set of defines. Defining the D3D defines pulls in the DX headers, which in turn pulls in the headers for IUnknown.

Again, really minor, but might save someone else in the same predicament some trouble 😅

[rpavlik]

so that’s a good question. The required headers/includes are marked up in the XML but aren’t being written to the header files for some reason. Can you open an issue for adding those includes to openxr_platform.h? It is annoying to work around for sure.

[amalon]

This issue also appears to affect users of the OpenXR headers, not just the loader itself. Somebody on the flightgear mailing list reported it with MSVC 2019 (16.11.18), with OpenXR 1.0.24: https://sourceforge.net/p/flightgear/mailman/message/37697116/ Visual studio community 2022 didn’t seem affected. Including unknwn.h before openxr_platform.h worked around it, but it seems flawed to expect openxr apps to anticipate includes that might be required on windows for extensions they don’t use or future extensions they may not know about.

Should the openxr_platform.h header not include unknwn.h itself?