Create MTLLibrary from raw String for use within RealityKit

Hello,

I have a usecase where I need to to download and compile metal shaders on demand as strings or .metal files. These should then be used for CustomMaterials and/or postprocessing within RealityKit. Essentially this boils down to having raw source code that needs to be compiled at runtime.

My plan was to use the method makeLibrary(source:options:completionHandler:) to accomplish this.

The problem is that I get the following error during compilation:

RealityKitARExperienceAssetProvider: An error occured while trying to compile shader library »testShaderLibrary«

- Error Domain=MTLLibraryErrorDomain Code=3 "program_source:2:10: fatal error: 'RealityKit/RealityKit.h' file not found

#include <RealityKit/RealityKit.h>

My code for creating the library looks like this (simplified example):

let librarySourceString: String = """
#include <metal_stdlib>
#include <RealityKit/RealityKit.h>

using namespace metal;

[[visible]]
void mySurfaceShader(realitykit::surface_parameters params)
{
    params.surface().set_base_color(half3(1, 1, 1));
}
"""

mtlDevice.makeLibrary(source: librarySourceString, options: nil) { library, error in
    if let error = error {
        dump(error)
        return
    }

    // do something with library
}

So I'm wondering if there's a way to tell the metal compiler how to resolve this reference to the RealityKit header file? Would I need to replace that part of the source string maybe with an absolute path to the RealityKit framework (if so – how would I get this at runtime)?

Appreciate any hints - thanks!