gfx-rs/wgpu · error

not implemented

Error message

not implemented

What it means

This is a Rust `unimplemented!()` panic in wgpu-hal's Metal backend inside `update_bind_group_state`. The backend explicitly does not handle ray-tracing shader stages (RayGeneration, AnyHit, ClosestHit, Miss) when mapping bind group resources per stage; Metal has no hardware ray tracing pipeline support in this backend, so these stages are hard-stubbed. Hitting it means a bind group was bound with a pipeline layout that included ray-tracing stage visibility.

Source

Thrown at wgpu-hal/src/metal/command.rs:327

    /// Updates the bindings for a single shader stage, called in `set_bind_group`.
    fn update_bind_group_state(
        &mut self,
        encoder: Encoder<'_>,
        index_base: super::ResourceData<u32>,
        bg_info: &super::BindGroupLayoutInfo,
        dynamic_offsets: &[wgt::DynamicOffset],
        group_index: u32,
        group: &super::BindGroup,
    ) {
        use naga::ShaderStage as S;
        let resource_indices = match encoder.stage() {
            S::Vertex => &bg_info.base_resource_indices.vs,
            S::Fragment => &bg_info.base_resource_indices.fs,
            S::Task => &bg_info.base_resource_indices.ts,
            S::Mesh => &bg_info.base_resource_indices.ms,
            S::Compute => &bg_info.base_resource_indices.cs,
            S::RayGeneration | S::AnyHit | S::ClosestHit | S::Miss => unimplemented!(),
        };
        let buffers = match encoder.stage() {
            S::Vertex => group.counters.vs.buffers,
            S::Fragment => group.counters.fs.buffers,
            S::Task => group.counters.ts.buffers,
            S::Mesh => group.counters.ms.buffers,
            S::Compute => group.counters.cs.buffers,
            S::RayGeneration | S::AnyHit | S::ClosestHit | S::Miss => unimplemented!(),
        };
        let mut changes_sizes_buffer = false;
        for index in 0..buffers {
            let res = &group.buffers[(index_base.buffers + index) as usize];
            match res {
                super::BufferLikeResource::Buffer {
                    ptr,
                    mut offset,
                    dynamic_index,
                    binding_size,

View on GitHub (pinned to 3e11ff59bf)

Solutions

1. Remove ray-tracing shader stages from all binding visibilities in the PipelineLayout used on Metal
2. Keep ray-tracing pipeline layouts behind a cfg/backend check and only construct them on backends that support ray tracing (Vulkan/DX12)
3. File or check an upstream issue for Metal ray tracing support; until then treat Metal as a non-ray-tracing backend

Example fix

// before
let layout = device.create_pipeline_layout(&PipelineLayoutDescriptor {
    bind_group_layouts: &[&bgl_with_rt_visibility],
    ..
});
// after
let bgl_desc.visibility = ShaderStages::VERTEX | ShaderStages::FRAGMENT; // drop RT stages on Metal

fn layout_is_metal_safe(layout: &PipelineLayoutDescriptor) -> bool {
    const RT: ShaderStages = ShaderStages::RAY_GENERATION | ShaderStages::ANY_HIT | ShaderStages::CLOSEST_HIT | ShaderStages::MISS;
    layout.bind_group_layouts.iter().flatten().all(|b| !b.visible_stages().intersects(RT))
}

fn uses_rt_stages(v: wgt::ShaderStages) -> bool {
    v.intersects(wgt::ShaderStages::RAY_GENERATION | wgt::ShaderStages::ANY_HIT | wgt::ShaderStages::CLOSEST_HIT | wgt::ShaderStages::MISS)
}

When it happens

Trigger: Calling `CommandEncoder::set_bind_group` (or render/compute pass bind group binding) on a Metal device while the pipeline layout has bindings whose `visibility` includes ShaderStages::RAY_GENERATION, ANY_HIT, CLOSEST_HIT, or MISS; the stage match arm falls through to `unimplemented!()` at wgpu-hal/src/metal/command.rs:327.

Common situations: Porting code written for the Vulkan or DX12 backends (where ray tracing is partially supported) to Metal; sharing a pipeline layout across backends; accidentally requesting ray-tracing visibility flags on bindings used in a Metal app.

Related errors

• Ray tracing pipelines are unsupported on Metal
• metal does not support vertex ray hit return
• not implemented
• not implemented
• ray tracing pipelines not yet implemented

AI-assisted analysis of gfx-rs/wgpu@3e11ff59bf (2026-09-03). Data as JSON: /api/errors/67f882ea463d42b0. Report an issue: GitHub.