[DRAFT] Implement XR_FB_space_warp extension

[devloglogan]

Adds an extension wrapper implementation of XR_FB_space_warp.

Setup

UPDATED (2024-12-12): Both mobile and compatibility renderers are now supported.

In order to test AppSW out (compatibility renderer only at the moment):

• Build Godot with one of the following PRs (depending on which renderer you'd like to test):
  • Implement motion vectors in compatibility renderer godotengine/godot#97151
  • Implement motion vectors in mobile renderer godotengine/godot#100283
• Switch the thirdparty/godot-cpp submodule of this repo to master branch

Then you should be able to build the plugin like normal. Currently in this PR, AppSW is enabled by default, so no need to enable it.

Debug View

UPDATED (2024-11-5): I've added a new Meta Space Warp sample project to this PR, feel free to use that for testing.

I've (minimally) added multiple scenarios of moving elements in the demo project (particles/multimesh/skeleton) for testing purposes. If you'd like a visual of the underlying motion vectors that are generated, you can use the following adb command.

adb shell setprop debug.oculus.spaceWarpDebug 1 && adb shell setprop debug.oculus.MVOverlay 4 && adb shell setprop debug.oculus.MVOverlay.Alpha 0.8 && adb shell input keyevent "KEYCODE_POWER" && adb shell input keyevent "KEYCODE_POWER"

Sometimes I find the project crashes when running the above command, but the debug view is visible upon restarting the app. To exit this view mode you can run:

adb shell setprop debug.oculus.spaceWarpDebug 0 && adb shell input keyevent "KEYCODE_POWER" && adb shell input keyevent "KEYCODE_POWER"

To Do

UPDATED (2024-11-5): These have all been completed.

• Account for locomotion by properly setting appSpaceDeltaPose.
• Enable the use of the XR_COMPOSITION_LAYER_SPACE_WARP_INFO_FRAME_SKIP_BIT_FB flag to skip frames of spacewarp.
• Have the extension not enabled by default, and determine the best way for users to enable/disable it.

[dsnopek]

Thanks, this is looking great so far!

Some additional notes about the demo

• I think this should get it's own sample rather than modifying the main "demo" project
• There is no plain MeshInstance3D moving, only the more advanced cases. We should have the simplest case shown too
• Having a button to enable/disable AppSW would be nice
• I think we should add a plane with a very busy texture (plaid?) behind all the moving objects to make the artifacts more obvious

[devloglogan]

@dsnopek I'd done the previous XR sample projects as their own PRs following the merging of the corresponding extensions. I had planned to just keep the simple test scene in the demo project while this PR remained as a draft. I see nothing wrong with expanding on it and just adding an XR sample project to this PR as well though! I will do that.

[devloglogan]

I've added a fair amount of updates:

• Moved the test scene into its own "Meta Space Warp" sample project, included in this PR.
  • Added a normal, moving MeshInstance3D to the scene
  • Space warp can now be enabled/disabled by pressing the A button.
  • Added movement/turning with the analog sticks.
  • Added a CC0 grass texture behind moving objects so users can see space warp artifacts more easily.
• Added a project setting for enabling space warp.
• Space warp is now automatically disabled if a non-opengl renderer is being used.
• Added a skip_space_warp_frame() function to skip space warp for the following frame.
• I believe I'm now accounting for locomotion correctly in appSpaceDeltaPose.

I will open this PR once godotengine/godot#97151 is merged!

[dsnopek]

Thanks!

This is starting to look really good! I especially like all the changes to the sample project - it'll make it very easy for developers to see the sort of artifacts that AppSW can generate, and seeing them also helps us confirm that things are doing what we would expect :-)

[m4gr3d]

Do we have a use-case for this setter, given space warp can also be enabled via the project settings?

[dsnopek]

Yes. There may be whole parts of the game where you do or don't want to use space warp. For example, in menus or other non-performance intensive areas, you may want to leave it off, and only turn it on when you enter real gameplay.

[devloglogan]

I've updated this PR (and the setup instructions in the description) so that it can also be used with the new mobile renderer motion vectors PR: godotengine/godot#100283

[dsnopek]

FYI, the tests are failing because it's using Godot v4.3 for the XrSim tests and this depends on Godot changes. So, we'll need to wait until there is a 4.4-dev release which includes godotengine/godot#100282 and then update the CI variable to use that version