wgpu::Features::DEBUG_PRINTF does not exist

[DeanRoddey]

I'm using 30.0.1 on Linux, over Vulkan 1.4. I've got the vulkan validation layer enabled, and I'm trying to get the WGSL shader debug feature enabled but everything keeps saying I have to set the wgpu::Features::DEBUG_PRINTF flag, but it doesn't exist. Nor does the wgpu::InstanceFlags::DEBUG_PRINTF flag.

Am I missing something here? If I try to enable printf in the shader it gives me:

unknown enable-extension `wgpu_debug_printf

Which I assume is not unexpected given I can't set the requested flags. I can open the features.rs source file can search it and there's no such flag in the file anywhere, so I assume it's just conditional'd out.

Anyhoo, any help would be much appreciated. I've struggled more with this than with getting an initial test app up and working.

[Arthur031221]

That error is expected with wgpu 30.0.1: neither wgpu::Features nor wgpu::InstanceFlags defines DEBUG_PRINTF, and Naga rejects enable wgpu_debug_printf; as an unknown WGSL extension. I reproduced both missing constants and the parser error against the released 30.0.1 crates. The validation layer's Debug Printf is a separate SPIR-V instrumentation path; Khronos documents GLSL, HLSL, and Slang inputs, which produce NonSemantic.DebugPrintf instructions. Enabling that layer cannot make wgpu_debug_printf legal WGSL in wgpu; there is no flag to turn on for this path.

[DeanRoddey]

Thanks. Just to to sum up, it just is broken and there's nothing to do about it until it's fixed?

[Firestar99]

wgpu_debug_printf seems to be a rather new feature in wgpu, I wasn't even aware it existed, but here's the official docs.

Have a look at our docs on debug printf and how to enable them. They were written at a time where wgsl didn't support debug printf debugging, so it's documenting how to enable it via the native-only PASSTHROUGH_SHADERS feature so wgpu wouldn't touch the SPIR-V and just pass it though, so the debug printf instructions remain.

Now there could be a way to make the new wgpu_debug_printf feature work, but I'd recommend asking that to the wgpu folks. (I'll go forward this question on their discord channel, let's see.)

[Firestar99]

Got sent this PR http://github.com/gfx-rs/wgpu/pull/9389