Implement software adapter selection

deno_webgpu/src/lib.rs

@@ -216,6 +216,7 @@ fn deserialize_features(features: &wgpu_types::Features) -> Vec<&'static str> {
 #[serde(rename_all = "camelCase")]
 pub struct RequestAdapterArgs {
     power_preference: Option<wgpu_types::PowerPreference>,
+    force_fallback_adapter: bool,
 }
 
 #[derive(Serialize)]
@@ -259,7 +260,7 @@ pub async fn op_webgpu_request_adapter(
             Some(power_preference) => power_preference.into(),
             None => PowerPreference::default(),
         },
-        // TODO(lucacasonato): respect forceFallbackAdapter
+        force_fallback_adapter: args.force_fallback_adapter,
         compatible_surface: None, // windowless
     };
     let res = instance.request_adapter(

player/src/bin/play.rs

@@ -55,6 +55,7 @@ fn main() {
                 .request_adapter(
                     &wgc::instance::RequestAdapterOptions {
                         power_preference: wgt::PowerPreference::LowPower,
+                        force_fallback_adapter: false,
                         #[cfg(feature = "winit")]
                         compatible_surface: Some(surface),
                         #[cfg(not(feature = "winit"))]

player/tests/test.rs

@@ -186,6 +186,7 @@ impl Corpus {
             let adapter = match global.request_adapter(
                 &wgc::instance::RequestAdapterOptions {
                     power_preference: wgt::PowerPreference::LowPower,
+                    force_fallback_adapter: false,
                     compatible_surface: None,
                 },
                 wgc::instance::AdapterInputs::IdSet(

wgpu-core/src/instance.rs

@@ -551,7 +551,34 @@ impl<G: GlobalIdentityHandlerFactory> Global<G> {
     ) -> Result<AdapterId, RequestAdapterError> {
         profiling::scope!("pick_adapter", "Instance");
 
-        let instance = &self.instance;
+        fn gather<A: HalApi, I: Clone>(
+            _: A,
+            instance: Option<&A::Instance>,
+            inputs: &AdapterInputs<I>,
+            compatible_surface: Option<&Surface>,
+            force_software: bool,
+            device_types: &mut Vec<wgt::DeviceType>,
+        ) -> (Option<I>, Vec<hal::ExposedAdapter<A>>) {
+            let id = inputs.find(A::VARIANT);
+            match instance {
+                Some(inst) if id.is_some() => {
+                    let mut adapters = unsafe { inst.enumerate_adapters() };
+                    if force_software {
+                        adapters.retain(|exposed| exposed.info.device_type == wgt::DeviceType::Cpu);
+                    }
+                    if let Some(surface) = compatible_surface {
+                        let suf_raw = &A::get_surface(surface).raw;
+                        adapters.retain(|exposed| unsafe {
+                            exposed.adapter.surface_capabilities(suf_raw).is_some()
+                        });
+                    }
+                    device_types.extend(adapters.iter().map(|ad| ad.info.device_type));
+                    (id, adapters)
+                }
+                _ => (id, Vec::new()),
+            }
+        }
+
         let mut token = Token::root();
         let (surface_guard, mut token) = self.surfaces.read(&mut token);
         let compatible_surface = desc
@@ -564,67 +591,51 @@ impl<G: GlobalIdentityHandlerFactory> Global<G> {
             .transpose()?;
         let mut device_types = Vec::new();
 
-        let mut id_vulkan = inputs.find(Backend::Vulkan);
-        let mut id_metal = inputs.find(Backend::Metal);
-        let mut id_dx12 = inputs.find(Backend::Dx12);
-        let mut id_dx11 = inputs.find(Backend::Dx11);
-        let mut id_gl = inputs.find(Backend::Gl);
-
-        backends_map! {
-            let map = |(instance_backend, id_backend, surface_backend)| {
-                match *instance_backend {
-                    Some(ref inst) if id_backend.is_some() => {
-                        let mut adapters = unsafe { inst.enumerate_adapters() };
-                        if let Some(surface_backend) = compatible_surface.and_then(surface_backend) {
-                            adapters.retain(|exposed| unsafe {
-                                exposed.adapter.surface_capabilities(&surface_backend.raw).is_some()
-                            });
-                        }
-                        device_types.extend(adapters.iter().map(|ad| ad.info.device_type));
-                        adapters
-                    }
-                    _ => Vec::new(),
-                }
-            };
-
-            // NB: The internal function definitions are a workaround for Rust
-            // being weird with lifetimes for closure literals...
         #[cfg(vulkan)]
-            let adapters_vk = map((&instance.vulkan, &id_vulkan, {
-                fn surface_vulkan(surf: &Surface) -> Option<&HalSurface<hal::api::Vulkan>> {
-                    surf.vulkan.as_ref()
-                }
-                surface_vulkan
-            }));
+        let (mut id_vulkan, adapters_vk) = gather(
+            hal::api::Vulkan,
+            self.instance.vulkan.as_ref(),
+            &inputs,
+            compatible_surface,
+            desc.force_fallback_adapter,
+            &mut device_types,
+        );
         #[cfg(metal)]
-            let adapters_mtl = map((&instance.metal, &id_metal, {
-                fn surface_metal(surf: &Surface) -> Option<&HalSurface<hal::api::Metal>> {
-                    surf.metal.as_ref()
-                }
-                surface_metal
-            }));
+        let (mut id_metal, adapters_metal) = gather(
+            hal::api::Metal,
+            self.instance.metal.as_ref(),
+            &inputs,
+            compatible_surface,
+            desc.force_fallback_adapter,
+            &mut device_types,
+        );
         #[cfg(dx12)]
-            let adapters_dx12 = map((&instance.dx12, &id_dx12, {
-                fn surface_dx12(surf: &Surface) -> Option<&HalSurface<hal::api::Dx12>> {
-                    surf.dx12.as_ref()
-                }
-                surface_dx12
-            }));
+        let (mut id_dx12, adapters_dx12) = gather(
+            hal::api::Dx12,
+            self.instance.dx12.as_ref(),
+            &inputs,
+            compatible_surface,
+            desc.force_fallback_adapter,
+            &mut device_types,
+        );
         #[cfg(dx11)]
-            let adapters_dx11 = map((&instance.dx11, &id_dx11, {
-                fn surface_dx11(surf: &Surface) -> Option<&HalSurface<hal::api::Dx11>> {
-                    surf.dx11.as_ref()
-                }
-                surface_dx11
-            }));
+        let (mut id_dx11, adapters_dx11) = gather(
+            hal::api::Dx11,
+            self.instance.dx11.as_ref(),
+            &inputs,
+            compatible_surface,
+            desc.force_fallback_adapter,
+            &mut device_types,
+        );
         #[cfg(gl)]
-            let adapters_gl = map((&instance.gl, &id_gl, {
-                fn surface_gl(surf: &Surface) -> Option<&HalSurface<hal::api::Gles>> {
-                    surf.gl.as_ref()
-                }
-                surface_gl
-            }));
-        }
+        let (mut id_gl, adapters_gl) = gather(
+            hal::api::Gles,
+            self.instance.gl.as_ref(),
+            &inputs,
+            compatible_surface,
+            desc.force_fallback_adapter,
+            &mut device_types,
+        );
 
         if device_types.is_empty() {
             return Err(RequestAdapterError::NotFound);
@@ -676,7 +687,7 @@ impl<G: GlobalIdentityHandlerFactory> Global<G> {
             #[cfg(vulkan)]
             map(("Vulkan", &mut id_vulkan, adapters_vk)),
             #[cfg(metal)]
-            map(("Metal", &mut id_metal, adapters_mtl)),
+            map(("Metal", &mut id_metal, adapters_metal)),
             #[cfg(dx12)]
             map(("Dx12", &mut id_dx12, adapters_dx12)),
             #[cfg(dx11)]
@@ -685,14 +696,7 @@ impl<G: GlobalIdentityHandlerFactory> Global<G> {
             map(("GL", &mut id_gl, adapters_gl)),
         }
 
-        let _ = (
-            selected,
-            id_vulkan.take(),
-            id_metal.take(),
-            id_dx12.take(),
-            id_dx11.take(),
-            id_gl.take(),
-        );
+        let _ = selected;
         log::warn!("Some adapters are present, but enumerating them failed!");
         Err(RequestAdapterError::NotFound)
     }

wgpu-types/src/lib.rs

@@ -131,6 +131,9 @@ impl From<Backend> for Backends {
 pub struct RequestAdapterOptions<S> {
     /// Power preference for the adapter.
     pub power_preference: PowerPreference,
+    /// Indicates that only a fallback adapter can be returned. This is generally a "software"
+    /// implementation on the system.
+    pub force_fallback_adapter: bool,
     /// Surface that is required to be presentable with the requested adapter. This does not
     /// create the surface, only guarantees that the adapter can present to said surface.
     pub compatible_surface: Option<S>,
@@ -140,6 +143,7 @@ impl<S> Default for RequestAdapterOptions<S> {
     fn default() -> Self {
         Self {
             power_preference: PowerPreference::default(),
+            force_fallback_adapter: false,
             compatible_surface: None,
         }
     }

wgpu/examples/hello-triangle/main.rs

@@ -12,6 +12,7 @@ async fn run(event_loop: EventLoop<()>, window: Window) {
     let adapter = instance
         .request_adapter(&wgpu::RequestAdapterOptions {
             power_preference: wgpu::PowerPreference::default(),
+            force_fallback_adapter: false,
             // Request an adapter which can render to our surface
             compatible_surface: Some(&surface),
         })

wgpu/examples/hello-windows/main.rs

@@ -66,9 +66,9 @@ async fn run(event_loop: EventLoop<()>, viewports: Vec<(Window, wgpu::Color)>) {
         .collect();
     let adapter = instance
         .request_adapter(&wgpu::RequestAdapterOptions {
-            power_preference: wgpu::PowerPreference::default(),
             // Request an adapter which can render to our surface
             compatible_surface: viewports.first().map(|desc| &desc.surface),
+            ..Default::default()
         })
         .await
         .expect("Failed to find an appropriate adapter");

wgpu/src/backend/direct.rs

@@ -777,6 +777,7 @@ impl crate::Context for Context {
         let id = self.0.request_adapter(
             &wgc::instance::RequestAdapterOptions {
                 power_preference: options.power_preference,
+                force_fallback_adapter: options.force_fallback_adapter,
                 compatible_surface: options.compatible_surface.map(|surface| surface.id.id),
             },
             wgc::instance::AdapterInputs::Mask(wgt::Backends::all(), |_| PhantomData),

wgpu/src/util/init.rs

@@ -79,6 +79,7 @@ pub async fn initialize_adapter_from_env_or_default(
             instance
                 .request_adapter(&RequestAdapterOptions {
                     power_preference: power_preference_from_env().unwrap_or_default(),
+                    force_fallback_adapter: false,
                     compatible_surface,
                 })
                 .await

wgpu/tests/instance.rs

@@ -12,6 +12,7 @@ fn request_adapter_inner(power: wgt::PowerPreference) {
 
     let _adapter = pollster::block_on(instance.request_adapter(&wgpu::RequestAdapterOptions {
         power_preference: power,
+        force_fallback_adapter: false,
         compatible_surface: None,
     }))
     .unwrap();