Gate DX12 mesh shader command signature initialization on device support. (#8297)

Author: vorporeal

CHANGELOG.md

@@ -40,6 +40,12 @@ Bottom level categories:
 
 ## Unreleased
 
+### Bug Fixes
+
+#### DX12
+
+- Fix device creation failures for devices that do not support mesh shaders. By @vorporeal in [#8297](https://github.com/gfx-rs/wgpu/pull/8297).
+
 ## v27.0.0 (2025-10-01)
 
 ### Major Changes

wgpu-hal/src/dx12/command.rs

@@ -1338,14 +1338,17 @@ impl crate::CommandEncoder for super::CommandEncoder {
 
         let cmd_list6: Direct3D12::ID3D12GraphicsCommandList6 =
             self.list.as_ref().unwrap().cast().unwrap();
-        let cmd_signature = &self
+        let Some(cmd_signature) = &self
             .pass
             .layout
             .special_constants
             .as_ref()
             .and_then(|sc| sc.indirect_cmd_signatures.as_ref())
             .unwrap_or_else(|| &self.shared.cmd_signatures)
-            .draw_mesh;
+            .draw_mesh
+        else {
+            panic!("Feature `MESH_SHADING` not enabled");
+        };
         unsafe {
             cmd_list6.ExecuteIndirect(cmd_signature, draw_count, &buffer.resource, offset, None, 0);
         }
@@ -1401,9 +1404,12 @@ impl crate::CommandEncoder for super::CommandEncoder {
         self.prepare_dispatch([0; 3]);
         let cmd_list6: Direct3D12::ID3D12GraphicsCommandList6 =
             self.list.as_ref().unwrap().cast().unwrap();
+        let Some(ref command_signature) = self.shared.cmd_signatures.draw_mesh else {
+            panic!("Feature `MESH_SHADING` not enabled");
+        };
         unsafe {
             cmd_list6.ExecuteIndirect(
-                &self.shared.cmd_signatures.draw_mesh,
+                command_signature,
                 max_count,
                 &buffer.resource,
                 offset,

wgpu-hal/src/dx12/device.rs

@@ -116,6 +116,24 @@ impl super::Device {
         // maximum number of CBV/SRV/UAV descriptors in heap for Tier 1
         let capacity_views = limits.max_non_sampler_bindings as u64;
 
+        let draw_mesh = if features
+            .features_wgpu
+            .contains(wgt::FeaturesWGPU::EXPERIMENTAL_MESH_SHADER)
+        {
+            Some(Self::create_command_signature(
+                &raw,
+                None,
+                size_of::<wgt::DispatchIndirectArgs>(),
+                &[Direct3D12::D3D12_INDIRECT_ARGUMENT_DESC {
+                    Type: Direct3D12::D3D12_INDIRECT_ARGUMENT_TYPE_DISPATCH_MESH,
+                    ..Default::default()
+                }],
+                0,
+            )?)
+        } else {
+            None
+        };
+
         let shared = super::DeviceShared {
             adapter,
             zero_buffer,
@@ -140,16 +158,7 @@ impl super::Device {
                     }],
                     0,
                 )?,
-                draw_mesh: Self::create_command_signature(
-                    &raw,
-                    None,
-                    size_of::<wgt::DispatchIndirectArgs>(),
-                    &[Direct3D12::D3D12_INDIRECT_ARGUMENT_DESC {
-                        Type: Direct3D12::D3D12_INDIRECT_ARGUMENT_TYPE_DISPATCH_MESH,
-                        ..Default::default()
-                    }],
-                    0,
-                )?,
+                draw_mesh,
                 dispatch: Self::create_command_signature(
                     &raw,
                     None,
@@ -1371,47 +1380,58 @@ impl crate::Device for super::Device {
                     };
                     size_of_val(&first_vertex) + size_of_val(&first_instance) + size_of_val(&other)
                 };
-                Some(super::CommandSignatures {
-                    draw: Self::create_command_signature(
+
+                let draw_mesh = if self
+                    .features
+                    .features_wgpu
+                    .contains(wgt::FeaturesWGPU::EXPERIMENTAL_MESH_SHADER)
+                {
+                    Some(Self::create_command_signature(
                         &self.raw,
                         Some(&raw),
-                        special_constant_buffer_args_len + size_of::<wgt::DrawIndirectArgs>(),
+                        special_constant_buffer_args_len + size_of::<wgt::DispatchIndirectArgs>(),
                         &[
                             constant_indirect_argument_desc,
                             Direct3D12::D3D12_INDIRECT_ARGUMENT_DESC {
-                                Type: Direct3D12::D3D12_INDIRECT_ARGUMENT_TYPE_DRAW,
+                                Type: Direct3D12::D3D12_INDIRECT_ARGUMENT_TYPE_DISPATCH_MESH,
                                 ..Default::default()
                             },
                         ],
                         0,
-                    )?,
-                    draw_indexed: Self::create_command_signature(
+                    )?)
+                } else {
+                    None
+                };
+
+                Some(super::CommandSignatures {
+                    draw: Self::create_command_signature(
                         &self.raw,
                         Some(&raw),
-                        special_constant_buffer_args_len
-                            + size_of::<wgt::DrawIndexedIndirectArgs>(),
+                        special_constant_buffer_args_len + size_of::<wgt::DrawIndirectArgs>(),
                         &[
                             constant_indirect_argument_desc,
                             Direct3D12::D3D12_INDIRECT_ARGUMENT_DESC {
-                                Type: Direct3D12::D3D12_INDIRECT_ARGUMENT_TYPE_DRAW_INDEXED,
+                                Type: Direct3D12::D3D12_INDIRECT_ARGUMENT_TYPE_DRAW,
                                 ..Default::default()
                             },
                         ],
                         0,
                     )?,
-                    draw_mesh: Self::create_command_signature(
+                    draw_indexed: Self::create_command_signature(
                         &self.raw,
                         Some(&raw),
-                        special_constant_buffer_args_len + size_of::<wgt::DispatchIndirectArgs>(),
+                        special_constant_buffer_args_len
+                            + size_of::<wgt::DrawIndexedIndirectArgs>(),
                         &[
                             constant_indirect_argument_desc,
                             Direct3D12::D3D12_INDIRECT_ARGUMENT_DESC {
-                                Type: Direct3D12::D3D12_INDIRECT_ARGUMENT_TYPE_DISPATCH_MESH,
+                                Type: Direct3D12::D3D12_INDIRECT_ARGUMENT_TYPE_DRAW_INDEXED,
                                 ..Default::default()
                             },
                         ],
                         0,
                     )?,
+                    draw_mesh,
                     dispatch: Self::create_command_signature(
                         &self.raw,
                         Some(&raw),

wgpu-hal/src/dx12/mod.rs

@@ -659,7 +659,7 @@ struct Idler {
 struct CommandSignatures {
     draw: Direct3D12::ID3D12CommandSignature,
     draw_indexed: Direct3D12::ID3D12CommandSignature,
-    draw_mesh: Direct3D12::ID3D12CommandSignature,
+    draw_mesh: Option<Direct3D12::ID3D12CommandSignature>,
     dispatch: Direct3D12::ID3D12CommandSignature,
 }