OpenXR - 6DoF support

[lvonasek]

Introduction

In PR https://github.com/hrydgard/ppsspp/pull/15659 I added support for OpenXR on Oculus Quest VR headsets. Intent of this PR is to add 6 dimensions of freedom for head movement (so players can look arround in the game). For now I use so called mono VR (the frames for both eyes are the same).

Tasks for this PR

• [x] Integrate head rotation
• [x] Integrate head movement
• [x] Render HUD and game layers separately

Tasks for the future PR(s)

• Do not use OPENXR define (code refactor)
• Geometry culling problem (probably not universally solvable)
• 3D stereo view (this will be optional and will cost some performance)

Related #11979, #15427

[lvonasek]

This is an equivalent to what I call build 012 in #vr-and-oculus-discussion.

@hrydgard, could you review it? Thank you.

[hrydgard]

Cool! I'll review this weekend.

[lvonasek]

Looks fairly close to be able to get it in but will need some refactoring either before or after merge as some comments indicate.

Thanks for review. Do you require to do the changes as part of this PR or could we continue resolving it in the future PR(s)?

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Also, it's a bit unfortunate to build yet another short-vector math lib, we already have one or two in the code base, but it's ok for now, can be refactored later.

The main advantage of having it in the codebase is you find the same in OpenXR sample codes and it is very nice if you can copy&paste piece of code and test it there.

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Really want to minimize the ifdef usage, since VR support will be a runtime toggle on Windows.

In this PR I removed the OPENXR ifdef from UI, I am going to remove it also from other places once I figure the best way to do that.

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And as I mentioned in one comment, the more logic we can put in GPU/Common as opposed to GPU/GLES, the better, since I want VR to work with Vulkan eventually (where I think we can do stereo more efficiently than in GL, though there might be enough multiview GL extensions?).

AFAIK Vulkan has no benefit against GL from multiview estensions. I am close to make multiview working on GL: https://github.com/lvonasek/ppsspp/tree/feature_openxr_stereo

There are only missing a few shader changes and passing matrices for both eyes.

[iota97]

Just wondering, if we get proper stereo rendering (not really sure if this is doing it already tbh) it would be nice to be able to access the different eyes in post processing shaders. In this way even with no VR it would be easy to set up thing like side by side or Cyan-Red glasses.

Not really that important, just tossing it here :)

[lvonasek]

Just wondering, if we get proper stereo rendering (not really sure if this is doing it already tbh) it would be nice to be able to access the different eyes in post processing shaders. In this way even with no VR it would be easy to set up thing like side by side or Cyan-Red glasses.

Not really that important, just tossing it here :)

The stereo is not ready yet. Stereo is an ongoing work in my other branch. There is going to be GL_TEXTURE_2D_ARRAY for the stereo framebuffer.

[lvonasek]

Do you require to do the changes as part of this PR or could we continue resolving it in the future PR(s)?

This question got overlooked. I am putting a small bug fixes into this branch to prevent merge madness if I created many small PRs. What do you think @hrydgard?

[hrydgard]

To answer your question that I didn't before, it does really bother me to have an "ifdef VR" right in the core of display timing.

Could accept some global variable though, which we set from elsewhere through an accessor function. Maybe g_InternalFrameRate. It could be interesting to experiment with different internal framerates even in non-VR (for example on 90Hz monitors).

[lvonasek]

Ok, I will do that.

[lvonasek]

To answer your question that I didn't before, it does really bother me to have an "ifdef VR" right in the core of display timing.

https://github.com/hrydgard/ppsspp/pull/15768/commits/2887671e6f4faf8aa53800c885d0ac58f1609826 Is this fine for you? If yes, I would really like to merge it.

[hrydgard]

Technically this "/ 1001" thing is part of the weird framerate 59.94 hz which is common due to legacy reasons. I don't think the Quest has a 71.93 or whatever framerate, for example. Though I guess that part hardly matters...

I'm sorry I haven't had time to fully review the latest version of this yet, but I will very soon.

[lvonasek]

Thank you, I will be away for about a week, so I so I will not be able to do any changes during that time.

Let me share my plans a bit: After this PR I plan three huge changes:

• Stereoscopy with multiview (this is already WIP but it is bigger than I thought because I will have to add code to framebuffers in PPSSPP code to support multiview)
• Getting rid of OPENXR ifdefs (I tried to do it already but I just found a way how to do it wrong, next time I will do it properly)
• Support for another Android VR headset (I plan to add support for on Pico Neo headsets, then it should be much easier to add another OpenXR device support)

Afterwards there should be just small PRs coming fixing VR support for specific games (mostly 2D/3D rendering separation which causes 99% of VR problems).

[hrydgard]

Sounds great!

As for the game specific tricks, we're gonna have to systemize it and cleanly separate it from the main emulation code as much as possible.

[lvonasek]

Agreed 💯. Once you merge this PR, I will create the draft for stereo PR. As the next PR will be full-feature VR version, I will do the OPENXR removal there.