Can I detect the backend used by wgpu?

[tseli0s]

Considering this crate uses wgpu underneath, is there a way to find out the current backend used by it?

[parasyte]

You have a few options!

If you don't need to do anything with the info (you're only interested to satisfy curiosity) you can use the RUST_LOG env var (with env_logger or tracing-subscriber) like this:

$ RUST_LOG='wgpu_core::instance=info' cargo run --package minimal-winit
    Finished dev [unoptimized + debuginfo] target(s) in 0.61s
     Running `target/debug/minimal-winit`
[2023-02-26T18:09:14Z INFO  wgpu_core::instance] Adapter Metal AdapterInfo { name: "Intel(R) HD Graphics 630", vendor: 0, device: 0, device_type: IntegratedGpu, driver: "", driver_info: "", backend: Metal }

$ RUST_LOG='wgpu_core::instance=info' WGPU_POWER_PREF=high cargo run --package minimal-winit
    Finished dev [unoptimized + debuginfo] target(s) in 0.57s
     Running `target/debug/minimal-winit`
[2023-02-26T18:10:11Z INFO  wgpu_core::instance] Adapter Metal AdapterInfo { name: "AMD Radeon Pro 560", vendor: 0, device: 0, device_type: DiscreteGpu, driver: "", driver_info: "", backend: Metal }

If you want to get access to this at runtime in code, the wgpu::Adapter::get_info() API offers some reflection capabilities. But we do not expose this directly through our API. It will need a fork or a design and PR to add some kind of middleware.

The adapter is created here, used for a few things and thrown away:

pixels/src/builder.rs

Lines 266 to 287 in 8605592

	let adapter = match wgpu::util::initialize_adapter_from_env(&instance, self.backend) {
	Some(adapter) => Some(adapter),
	None => {
	instance
	.request_adapter(&request_adapter_options.as_ref().map_or_else(
	|| wgpu::RequestAdapterOptions {
	compatible_surface,
	force_fallback_adapter: false,
	power_preference:
	wgpu::util::power_preference_from_env().unwrap_or_default(),
	},
	|rao| wgpu::RequestAdapterOptions {
	compatible_surface: rao.compatible_surface.or(compatible_surface),
	force_fallback_adapter: rao.force_fallback_adapter,
	power_preference: rao.power_preference,
	},
	))
	.await
	}
	};
	let adapter = adapter.ok_or(Error::AdapterNotFound)?;

[tseli0s]

What I wanted is save it into my game's log if needed so it's a middleground between the two. Maybe I'll make a PR to expose the adapter information through a function, if that's okay with you ofc.

[parasyte]

I don't know what a good middleware API for this would look like. You can see the adapter is not stored anywhere outside of the builder. We don't need it for anything. Even if the AdapterInfo struct is stored, we don't need that either. It would just be holding on to extra state for a method that won't be called by most users.

There are a few other intermediate state items that the builder doesn't keep around. Namely wgpu::Instance, but also stuff like wgpu::SurfaceCapabilities.

Maybe the builder should accept some FnMut() closures that can be executed as "hooks" in the builder() method?

let adapter_info = None;
let pixels = PixelsBuilder::new(width, height, surface_texture)
    .with_adapter_hook(|adapter| {
        *adapter_info = Some(adapter.get_info());
    }
    .build()?;

// Do something with `adapter_info`
if let Some(adapter_info) = adapter_info {
    println!("{adapter_info:?}");
}

I don't really love it, but I haven't thought of anything better.