Mesh shading

wgpu exposes an experimental mesh-shading pipeline, mirroring DirectX 12 and Vulkan's mesh/task shader stages. Like ray tracing, it is experimental — the API is marked 🧪EXPERIMENTAL🧪 and the design is in flux.

docs/api-specs/mesh_shading.md is the authoritative spec.

What's exposed

A new pipeline shape with:

• An optional task stage (sometimes called amplification) that decides how many mesh-shader workgroups to dispatch per input primitive.
• A mesh stage that emits triangles directly, replacing the traditional vertex stage.
• An ordinary fragment stage as in the regular pipeline.

The relevant features in wgpu-types/src/features.rs:

• Features::EXPERIMENTAL_MESH_SHADER
• Features::EXPERIMENTAL_MESH_SHADER_MULTIVIEW
• Plus capability bits on Limits for max mesh outputs, max payload size, etc.

Backend support

Backend	Status
Vulkan	VK_EXT_mesh_shader. Requires a recent driver.
DX12	DirectX 12 mesh shaders. Requires SM 6.5+ and an Agility SDK runtime.
Metal	Mesh shaders (added in Metal 3 / macOS 13+). Selectively enabled.
GLES	Not supported.
WebGPU (browser)	Not exposed in the spec yet; experimental on a per-browser basis.

Implementation map

Layer	Files
wgpu API	wgpu/src/api/render_pipeline.rs (mesh-shader pipeline descriptors), wgpu/src/api/render_pass.rs (draw_mesh_tasks*)
wgpu-core	render pipeline construction in wgpu-core/src/pipeline.rs and wgpu-core/src/command/render.rs (mesh-task dispatch path)
wgpu-hal	per-backend trait methods for dispatch_mesh_*; per-backend pipeline construction with a mesh stage
wgpu-types	Features bits, Limits fields
naga	EntryPoint's stage includes ShaderStage::Mesh and ShaderStage::Task; per-backend emission of mesh outputs

Example

examples/features/src/mesh_shader/ is the canonical example. It demonstrates:

• Compiling mesh + task + fragment stages from a single WGSL file.
• Setting up a mesh-shader pipeline.
• Dispatching mesh tasks via draw_mesh_tasks on a render pass.

Naga support

Naga's IR has dedicated entry-point stages (ShaderStage::Mesh, ShaderStage::Task) and a Capabilities::MESH_SHADER / Capabilities::TASK_SHADER pair. Each shading-language backend emits the right pragmas/qualifiers:

• HLSL: [OutputTopology("triangle")] + SetMeshOutputCounts + mesh struct outputs.
• MSL: Mesh stage with mesh_grid_properties + [[mesh]] attribute.
• SPIR-V: OpExtension VK_EXT_mesh_shader + OpCapability MeshShadingEXT.

The validator (naga/src/valid/interface.rs) checks that the entry-point I/O matches the stage rules: a mesh entry point must declare its output topology, a task entry point must dispatch to a mesh entry point, etc.

Testing

• The example doubles as an integration test (cargo xtask test --bin wgpu-examples mesh_shader).
• Adapter-level expectations gate the test on backends that support the feature.
• CTS coverage is limited; the WebGPU spec hasn't promoted mesh shading to a core extension yet.

Caveats

• Experimental. Expect breaking changes between wgpu releases.
• Driver maturity varies; mesh-shader code paths are newer than rasterization paths and have more outstanding driver bugs.
• HLSL output for mesh shaders is one of the more complex code paths in naga::back::hlsl; check naga/tests/in/wgsl/mesh_shader*.wgsl and the corresponding .out/ for the generated output.