Add capability to function as a guest in Metal

WIP

piet-gpu-hal/src/lib.rs

@@ -16,7 +16,7 @@ mod macros;
 mod mux;
 
 pub use crate::mux::{
-    DescriptorSet, Fence, Instance, Pipeline, QueryPool, Sampler, Semaphore, ShaderCode, Surface,
+    DescriptorSet, Device, Fence, Instance, Pipeline, QueryPool, Sampler, Semaphore, ShaderCode, Surface,
     Swapchain,
 };
 pub use bufwrite::BufWrite;

piet-gpu-hal/src/metal.rs

@@ -153,6 +153,33 @@ impl MtlInstance {
     pub fn device(&self, _surface: Option<&MtlSurface>) -> Result<MtlDevice, Error> {
         if let Some(device) = metal::Device::system_default() {
             let cmd_queue = device.new_command_queue();
+            Ok(MtlDevice::new_from_raw_mtl(device, cmd_queue))
+        } else {
+            Err("can't create system default Metal device".into())
+        }
+    }
+
+    pub unsafe fn swapchain(
+        &self,
+        _width: usize,
+        _height: usize,
+        device: &MtlDevice,
+        surface: &MtlSurface,
+    ) -> Result<MtlSwapchain, Error> {
+        surface.layer.set_device(&device.device);
+        let n_drawables = surface.layer.maximum_drawable_count() as usize;
+        Ok(MtlSwapchain {
+            layer: surface.layer.to_owned(),
+            cmd_queue: device.cmd_queue.clone(),
+            drawable: Default::default(),
+            n_drawables,
+            drawable_ix: 0,
+        })
+    }
+}
+
+impl MtlDevice {
+    pub fn new_from_raw_mtl(device: metal::Device, cmd_queue: metal::CommandQueue) -> MtlDevice {
         let is_mac = device.supports_feature_set(MTLFeatureSet::macOS_GPUFamily1_v1);
         let is_ios = device.supports_feature_set(MTLFeatureSet::iOS_GPUFamily1_v1);
         let version = NSOperatingSystemVersion::get();
@@ -182,34 +209,13 @@ impl MtlInstance {
         let helpers = Arc::new(Helpers {
             clear_pipeline: clear::make_clear_pipeline(&device),
         });
-            Ok(MtlDevice {
+        MtlDevice {
             device,
             cmd_queue: Arc::new(Mutex::new(cmd_queue)),
             gpu_info,
             helpers,
-            })
-        } else {
-            Err("can't create system default Metal device".into())
         }
     }
-
-    pub unsafe fn swapchain(
-        &self,
-        _width: usize,
-        _height: usize,
-        device: &MtlDevice,
-        surface: &MtlSurface,
-    ) -> Result<MtlSwapchain, Error> {
-        surface.layer.set_device(&device.device);
-        let n_drawables = surface.layer.maximum_drawable_count() as usize;
-        Ok(MtlSwapchain {
-            layer: surface.layer.to_owned(),
-            cmd_queue: device.cmd_queue.clone(),
-            drawable: Default::default(),
-            n_drawables,
-            drawable_ix: 0,
-        })
-    }
 }
 
 impl crate::backend::Device for MtlDevice {

piet-gpu-hal/src/mux.rs

@@ -208,6 +208,11 @@ impl Instance {
 // but not doing so lets us diverge more easily (at the moment, the divergence is
 // missing functionality).
 impl Device {
+    #[cfg(target_os = "macos")]
+    pub fn new_from_raw_mtl(device: &::metal::DeviceRef, queue: &::metal::CommandQueueRef) -> Device {
+        Device::Mtl(metal::MtlDevice::new_from_raw_mtl(device.to_owned(), queue.to_owned()))
+    }
+
     pub fn query_gpu_info(&self) -> GpuInfo {
         mux_match! { self;
             Device::Vk(d) => d.query_gpu_info(),