Mesh shaders MSL writer

examples/features/src/mesh_shader/mod.rs

@@ -38,18 +38,6 @@ fn compile_hlsl(device: &wgpu::Device, entry: &str, stage_str: &str) -> wgpu::Sh
     }
 }
 
-fn compile_msl(device: &wgpu::Device, entry: &str) -> wgpu::ShaderModule {
-    unsafe {
-        device.create_shader_module_passthrough(wgpu::ShaderModuleDescriptorPassthrough {
-            entry_point: entry.to_owned(),
-            label: None,
-            msl: Some(std::borrow::Cow::Borrowed(include_str!("shader.metal"))),
-            num_workgroups: (1, 1, 1),
-            ..Default::default()
-        })
-    }
-}
-
 pub struct Example {
     pipeline: wgpu::RenderPipeline,
 }
@@ -61,7 +49,7 @@ impl crate::framework::Example for Example {
         _queue: &wgpu::Queue,
     ) -> Self {
         let (ts, ms, fs, ts_name, ms_name, fs_name) = match adapter.get_info().backend {
-            wgpu::Backend::Vulkan => (
+            wgpu::Backend::Vulkan | wgpu::Backend::Metal => (
                 compile_wgsl(device),
                 compile_wgsl(device),
                 compile_wgsl(device),
@@ -77,14 +65,6 @@ impl crate::framework::Example for Example {
                 "main",
                 "main",
             ),
-            wgpu::Backend::Metal => (
-                compile_msl(device, "taskShader"),
-                compile_msl(device, "meshShader"),
-                compile_msl(device, "fragShader"),
-                "main",
-                "main",
-                "main",
-            ),
             _ => panic!("Example can currently only run on vulkan, dx12 or metal"),
         };
         let pipeline_layout = device.create_pipeline_layout(&wgpu::PipelineLayoutDescriptor {

naga/src/back/msl/mod.rs

@@ -178,6 +178,7 @@ enum ResolvedBinding {
         interpolation: Option<ResolvedInterpolation>,
     },
     Resource(BindTarget),
+    Payload,
 }
 
 #[derive(Copy, Clone)]
@@ -237,6 +238,8 @@ pub enum Error {
     ResolveArraySizeError(#[from] crate::proc::ResolveArraySizeError),
     #[error("entry point with stage {0:?} and name '{1}' not found")]
     EntryPointNotFound(ir::ShaderStage, String),
+    #[error("Cannot use mesh shader syntax prior to MSL 3.0")]
+    UnsupportedMeshShader,
 }
 
 #[derive(Clone, Debug, PartialEq, thiserror::Error)]
@@ -275,6 +278,9 @@ enum LocationMode {
     /// Output from the fragment shader.
     FragmentOutput,
 
+    /// Output from the mesh shader.
+    MeshOutput,
+
     /// Compute shader input or output.
     Uniform,
 }
@@ -551,7 +557,7 @@ impl Options {
                 interpolation,
                 sampling,
                 blend_src,
-                per_primitive: _,
+                per_primitive,
             } => match mode {
                 LocationMode::VertexInput => Ok(ResolvedBinding::Attribute(location)),
                 LocationMode::FragmentOutput => {
@@ -563,7 +569,9 @@ impl Options {
                         blend_src,
                     })
                 }
-                LocationMode::VertexOutput | LocationMode::FragmentInput => {
+                LocationMode::VertexOutput
+                | LocationMode::FragmentInput
+                | LocationMode::MeshOutput => {
                     Ok(ResolvedBinding::User {
                         prefix: if self.spirv_cross_compatibility {
                             "locn"
@@ -577,7 +585,11 @@ impl Options {
                             // sampling is `None` only for Flat interpolation.
                             let interpolation = interpolation.unwrap();
                             let sampling = sampling.unwrap_or(crate::Sampling::Center);
-                            Some(ResolvedInterpolation::from_binding(interpolation, sampling))
+                            Some(ResolvedInterpolation::from_binding(
+                                interpolation,
+                                sampling,
+                                per_primitive,
+                            ))
                         },
                     })
                 }
@@ -714,6 +726,7 @@ impl ResolvedBinding {
                     Bi::CullPrimitive => "primitive_culled",
                     // TODO: figure out how to make this written as a function call
                     Bi::PointIndex | Bi::LineIndices | Bi::TriangleIndices => unimplemented!(),
+                    // These aren't real builtins that backends are aware of
                     Bi::MeshTaskSize
                     | Bi::VertexCount
                     | Bi::PrimitiveCount
@@ -755,17 +768,26 @@ impl ResolvedBinding {
                     return Err(Error::UnimplementedBindTarget(target.clone()));
                 }
             }
+            Self::Payload => write!(out, "payload")?,
         }
         write!(out, "]]")?;
         Ok(())
     }
 }
 
 impl ResolvedInterpolation {
-    const fn from_binding(interpolation: crate::Interpolation, sampling: crate::Sampling) -> Self {
+    const fn from_binding(
+        interpolation: crate::Interpolation,
+        sampling: crate::Sampling,
+        per_primitive: bool,
+    ) -> Self {
         use crate::Interpolation as I;
         use crate::Sampling as S;
 
+        if per_primitive {
+            return Self::Flat;
+        }
+
         match (interpolation, sampling) {
             (I::Perspective, S::Center) => Self::CenterPerspective,
             (I::Perspective, S::Centroid) => Self::CentroidPerspective,