Based on what I read in https://developer.apple.com/documentation/RealityKit/validating-usd-files, the APIs that Apple provides don't (currently?) provide any support for writing out USD files, and specifically for variants - the tooling of the various renderers allows you to select between variants, but it expects the variants to already be defined within the USD file. There is a Entity.write(to: URL) capability that is new this year, but it creates a proprietary .reality format that isn't a stock USD(a/z) file. Based on my digging, the .reality file is a possibly a super-set of USD, because when it was created, the analog to capabilities needed in RealityKit didn't exist in the USD spec. Which may be (I suspect) still the case today.

Filed FB14532217

After putting together the project, and thinking "Oh, I should try the released Xcode in case this is a regression...", I found that it is, in fact, a regression in Xcode. I've updated the sample project - which now has a separate project built with Xcode 15.4, alongside the original which I started with Xcode 16b5 (and doesn't open in 15.4 because of that). When the same code and setup is built and run with Xcode 15.4, it works perfectly. The project created in Xcode 15.4 compiles and runs correctly when built with Xcode 16 beta 5, but the project created in Xcode 16 beta 5 doesn't set up the correct structure or something, and doesn't embed the resource. (I've submitted feedback with the details : FB14860256)

It seems to be more related to a regression or change in Xcode 16 beta 5 vs Xcode 15.4 than that. In Xcode 15.4, it works perfectly, regardless of the name of the folder. When I rename the file and compile in Xcode 16 beta, using either the new format Xcode project or old one, it doesn't appear to be loading correctly. I've updated the sample project to change the name of the directory, but it doesn't appear to make a difference, and the product built by Xcode 16 still fails to include the resource and present it. There appear to be perhaps multiple issues at play. After renaming the directory to prairie.skybox for this example - when the older Xcodeproj is built and run from Xcode 16, there's a different error reported - although the resource is correctly embedded: Unable to load resource: Reality File version 11 is not supported. (Latest supported version is 9.) It is all working - regardless of the name of the skybox directory - when built and run from Xcode 15.4.

I was just hitting the same issue recently, found this, and noted a possible solution. Using Xcode 15.4, when I used the -derivedDataPath argument, DONT specify the value with an = sign. For example: mkdir -p myDD xcodebuild -scheme MyApp -derivedDataPath ./myDD test worked as I hoped it might

My error here was in how I created the Signposter. To get a segment to show up on the PointsOfInterest in the profiler, you need to create it with the preset category of .pointsOfInterest. For example, instead of: signposter = OSSignposter(logger: logger) I should have set it: signposter = OSSignposter(subsystem: "MySubsystem", category: .pointsOfInterest) (thank you James Dempsey) - who also pointed out that I could add the different os_signpost instrument to see the ones that I'd created with the original method. They just didn't show up in the PointsOfInterest segment of the time profiler.