Add support for Direct3D 12 OpenXR backend

[mbucchia]

Add support for Direct3D 12 OpenXR backend and rendering with view
instancing (#86283). See godotengine/godot-proposals#10078.

This change adds support for running XR projects built with the d3d12
rendering backend. The XR backend hooks into the setup for the D3D12
render context in order to use the desired device and command queue for
submission to OpenXR. The XR backend takes care of importing the D3D12
swapchain images into the render context.

As part of this process, three issues are addressed:

• Ensuring that resource state transitions are only done on textures
  that require them.
• Enabling view instancing in the PSOs for multiview render passes.
• Addressing a bug in the D3D12 runtime where PSO creation may fail
  when front face detection is used.

Please refer to #86283 for additional discussions on the implementation
details.

----8<----8<----8<----8<----8<----8<----8<----8<----8<----8<----8<----
(remove content below from commit message when squashing this pull request)

For testing, I have been using the https://github.com/GodotVR/godot-xr-template and set it up for D3D12 rendering:

--- a/project.godot
+++ b/project.godot
@@ -54,8 +54,12 @@ common/drop_mouse_on_gui_input_disabled=true

 [rendering]

-renderer/rendering_method="gl_compatibility"
-renderer/rendering_method.mobile="gl_compatibility"
+rendering_device/driver="d3d12"
+rendering_device/driver.windows="d3d12"
+;rendering_device/d3d12/agility_sdk_version=615
+rendering_device/fallback_to_vulkan=false
+rendering_device/fallback_to_opengl3=false
+renderer/rendering_method.mobile="forward_plus"
 textures/vram_compression/import_etc2_astc=true
 environment/defaults/default_environment="res://default_env.tres"

Testing:

• Nvidia Ada Lovelace + godot-xr-template + Virtual Desktop (VDXR): PASS
• Nvidia Ada Lovelace + godot-xr-template + Varjo: PASS
• Nvidia Ada Lovelace + godot-xr-template + Meta XR Simulator: PASS
• Nvidia Ada Lovelace + godot-xr-template + Meta Quest Link: PASS
• Nvidia Ada Lovelace + godot-xr-template + SteamVR: PASS
• Nvidia Ada Lovelace + godot-xr-template + Windows Mixed Reality: FAIL [1]
• AMD RDNA2 + godot-xr-template + SteamVR: PENDING
• Intel Arc + godot-xr-template + SteamVR: PENDING
• godot-xr-template + Agility SDK 615: PASS
• godot-xr-template + --gpu-validation: PASS

I will perform the PENDING scenarios above once we are closer to merging (these scenarios require me to swap GPU).

[1] Disappointingly, there is an issue with WMR and we crash in xrCreateSwapchain() pretty inexplicably.
Looking into it now, I do not believe it is a bug with this change however.

[mbucchia]

Looking into workflow failures that seem to be due to the use of XrGraphicsRequirementsD3D12KHR.

Update: the clang and MingW build issues are resolved and base workflow passes.

[mbucchia]

I am a little confused by your CI.

This workflow with latest push passed all green:

https://github.com/mbucchia/godot/actions/runs/13881066387

However the checks below in the PR reflect a CSS error. The details show the formatter replacing #ifdef inclusion guards with #pragma once.

Meanwhile your CSS guide (https://docs.godotengine.org/en/latest/contributing/development/cpp_usage_guidelines.html#pragma-once-directive) says:

#pragma once directive
To follow the existing style, please use standard #ifdef-based include guards instead of #pragma once in new files

What am I missing?

[mbucchia]

Oh I think I get it - the passing run is from my forked repo. And running the workflow on the Godot repo requires an approval, so the current results are not reflecting the latest push.

[lawnjelly]

4.x very recently changed to #pragma once instead of header guards (#102298), the documentation may be out of date.

[mbucchia]

4.x very recently changed to #pragma once instead of header guards (#102298), the documentation may be out of date.

Understood. I will change my new files to use the pragmas. Thanks!

[BastiaanOlij]

Just giving this a first look and all seems pretty good. I don't know the DX12 backend well enough to give any insight on that so will need @clayjohn or @DarioSamo to verify the changes.

I'll find some time to do some testing on my end this week.

Re your comment here: #86283 (comment)
With WMR itself defuncts, do we want to put hacks like this in or just make note of them for anyone that wants to custom build for WMR?
I'm assuming here that SteamVR and other PC OpenXR runtimes will work with DX12 as well, the main goal here would be for those who wish to use the DX12 renderer on windows to be able to do VR with Godot.

[mbucchia]

Thank you Bastiaan! Please suggest some more testing as well if you want. I saw a couple of XR demo samples, maybe I will give those a shot. If you have a stress test let me know.

Re your comment here: #86283 (comment)
With WMR itself defuncts, do we want to put hacks like this in or just make note of them for anyone that wants to custom build for WMR?

I'm a little bit torn yeah. I think you really want to get rid of this warning message that calls specifically incompatibility with WMR today. D3D support was an avenue for that.

But also as I mentioned, I don't know if the issue will remain specific to WMR if a platform begins to use D3D12 as its internal gfx API in the future. There is none today AFAICT (most use D3D11 for composition inside the runtime). I might talk some more to the D3D team at Microsoft about these scenarios of "mixed usage" of Agility SDK. Definitely nothing actionable on the current PR though.