MTLResourceID should expose _impl

[Jasper-Bekkers]

For FFI reasons its often useful to be able to get access to the raw value, at the moment I'm just transmuting the struct back and forth but nicer would be to have a to_raw() -> u64

[madsmtm]

I believe our generation is correct here in hiding the field, that's also what Apple's docs show.

But the again, Swift's generation still allows constructing it with the private name. I suspect that's a bug in Swift's generation though, private fields seems like a fairly rare case, I only found three in our currently generated files?

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Anyhow, I'm fine with exposing from_raw and to_raw, though I think from_raw would have to be unsafe, from reading the docs on MTLResourceID:

A MTLResourceID represents a specific GPU resource, mutating this handle is undefined unless the mutation results in the value equalling an already existing handle of the same resource type.

I don't actually know if that's correct, haven't used this API myself and not too familiar with Metal, what do you think?

[Jasper-Bekkers]

I believe our generation is correct here in hiding the field, that's also what Apple's docs show.

I think so too, there are some apple provided libraries though that access the field directly. (Metal Shader Converter), which is why we need it in our saxaboom crate.

But the again, Swift's generation still allows constructing it with the private name. I suspect that's a bug in Swift's generation though, private fields seems like a fairly rare case, I only found three in our currently generated files?

---

Anyhow, I'm fine with exposing from_raw and to_raw, though I think from_raw would have to be unsafe, from reading the docs on MTLResourceID:

A MTLResourceID represents a specific GPU resource, mutating this handle is undefined unless the mutation results in the value equalling an already existing handle of the same resource type.

I don't actually know if that's correct, haven't used this API myself and not too familiar with Metal, what do you think?

I don't mind marking from_raw as unsafe, and I've done similar for similar constructs in our engine.

[MarijnS95]

@madsmtm for completeness Apple "exposes" and "uses" it here in their IRConverter runtime headers:

https://github.com/Traverse-Research/saxaboom/blob/2217a09e84e842e75231c5817bb94f7545577d6c/bindings_generator/vendor/metal_irconverter_runtime/metal_irconverter_runtime.h#L79

https://github.com/Traverse-Research/saxaboom/blob/2217a09e84e842e75231c5817bb94f7545577d6c/bindings_generator/vendor/metal_irconverter_runtime/metal_irconverter_runtime.h#L657-L660