gfx-rs/wgpu · error

Feature `RAY_TRACING` not enabled

Error message

Feature `RAY_TRACING` not enabled

What it means

`read_acceleration_structure_compact_size` calls `.expect("Feature `RAY_TRACING` not enabled")` on `device.extension_fns.ray_tracing`. This Option is only `Some` when the Vulkan device was created with the ray tracing extensions (e.g. VK_KHR_acceleration_structure/KHR_ray_query) and their function pointers were loaded. Panicking here means a compact-size query was requested for an acceleration structure without ray tracing support being enabled on the device.

Source

Thrown at wgpu-hal/src/vulkan/command.rs:496

            self.device.raw.cmd_write_timestamp(
                self.active,
                vk::PipelineStageFlags::BOTTOM_OF_PIPE,
                set.raw,
                index,
            )
        };
    }
    unsafe fn read_acceleration_structure_compact_size(
        &mut self,
        acceleration_structure: &super::AccelerationStructure,
        buffer: &super::Buffer,
    ) {
        let ray_tracing_functions = self
            .device
            .extension_fns
            .ray_tracing
            .as_ref()
            .expect("Feature `RAY_TRACING` not enabled");
        let query_pool = acceleration_structure
            .compacted_size_query
            .as_ref()
            .unwrap();
        unsafe {
            self.device
                .raw
                .cmd_reset_query_pool(self.active, *query_pool, 0, 1);
            ray_tracing_functions
                .acceleration_structure
                .cmd_write_acceleration_structures_properties(
                    self.active,
                    &[acceleration_structure.raw],
                    vk::QueryType::ACCELERATION_STRUCTURE_COMPACTED_SIZE_KHR,
                    *query_pool,
                    0,
                );
            self.device.raw.cmd_copy_query_pool_results(

View on GitHub (pinned to 3e11ff59bf)

Solutions

1. Request `Features::RAY_TRACING` in the DeviceDescriptor and confirm `Adapter::features()` advertises it before enabling
2. Check `adapter.features().contains(Features::RAY_TRACING)` before creating a device or calling compact-size queries
3. Ensure the Vulkan driver/GPU supports VK_KHR_acceleration_structure and VK_KHR_ray_query (RTX-class hardware, up-to-date driver)
4. Gate ray-tracing code paths behind a capability check and provide a non-RT fallback

Example fix

// before: panics if RT not enabled
coder.read_acceleration_structure_compact_size(as_gpu, &query);
// after: guard on the feature
if device.features().contains(wgpu::Features::RAY_TRACING) {
    encoder.read_acceleration_structure_compact_size(as_gpu, &query);
}

if !adapter.features().contains(wgpu::Features::RAY_TRACING) {
    return Err(Error::RayTracingUnsupported);
}

fn supports_ray_tracing(features: wgpu::Features) -> bool {
    features.contains(wgpu::Features::RAY_TRACING)
}

// panic-based; avoid catching. Assert capability at device creation instead:
assert!(device.features().contains(wgpu::Features::RAY_TRACING),
        "ray tracing required");

When it happens

Trigger: Calling `CommandEncoder::read_acceleration_structure_compact_size` (wgpu's ray-tracing API) on a device created without `Features::RAY_TRACING` (or where `extension_fns.ray_tracing` was None because extensions/functions were unavailable at device init).

Common situations: Using wgpu's experimental ray tracing API on a device/GPU/driver without VK_KHR_acceleration_structure or ray query support; forgetting to request `Features::RAY_TRACING` in `DeviceDescriptor`; running on adapters where the feature was filtered out by `adapter_features`.

Related errors

• Feature `EXPERIMENTAL_RAY_TRACING` not enabled
• Buffers are required to build acceleration structures
• This vulkan device is affected by [#8333](https://github.com
• vkFreeDescriptorSets error: {err}, please report this error
• {}

AI-assisted analysis of gfx-rs/wgpu@3e11ff59bf (2026-09-03). Data as JSON: /api/errors/2d26be308a5c99c8. Report an issue: GitHub.