WGPU error on switching materials with normal prepass

[johnbchron]

Bevy version

v0.11.0

[Optional] Relevant system information

• Rust Version: 1.73.0-nightly (d78bbf4bd 2023-08-03)
• OS: arch-ish
• Adapter info: AdapterInfo { name: "Intel(R) HD Graphics 520 (SKL GT2)", vendor: 32902, device: 6422, device_type: IntegratedGpu, driver: "Intel open-source Mesa driver", driver_info: "Mesa 23.0.4", backend: Vulkan }

What you did

To reproduce, set up a 3D camera with a NormalPrepass component on it. Define a custom material that uses a WGSL fragment. Spawn a scene (I'm not sure what data is important here, but it doesn't work with just a cube; might be UVs), and then set up a system to switch out the StandardMaterial for a CustomMaterial on any entity that has a StandardMaterial. Bevy crashes.

Minimum reproducible here.

What went wrong

This error occurs:

2023-08-09T20:52:12.883651Z ERROR wgpu::backend::direct: Handling wgpu errors as fatal by default
thread 'Compute Task Pool (1)' panicked at /home/jlewis/.cargo/registry/src/index.crates.io-6f17d22bba15001f/wgpu-0.16.3/src/backend/direct.rs:3019:5:
wgpu error: Validation Error

Caused by:
    In Device::create_render_pipeline
      note: label = `prepass_pipeline`
    Error matching ShaderStages(FRAGMENT) shader requirements against the pipeline
    Location[2] is provided by the previous stage output but is not consumed as input by this stage.


note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Encountered a panic in system `bevy_render::render_resource::pipeline_cache::PipelineCache::process_pipeline_queue_system`!
thread 'Compute Task Pool (0)' panicked at /home/jlewis/.cargo/registry/src/index.crates.io-6f17d22bba15001f/bevy_render-0.11.0/src/pipelined_rendering.rs:135:45:
called `Result::unwrap()` on an `Err` value: RecvError

Additional information

Honestly no clue :(

[idobenamram]

hey, im thinking of working on this issue. Able to reproduce the problem on my machine with your example!

[idobenamram]

hey, still working on it but it looks like it specifically doesn't work with the SceneBundle. you can also easily recreate the behavior
on the load_gltf.rs example.

[johnbchron]

How interesting. Thanks for working on it!

I forgot to include this in the original comment but my workaround was to manually specify the prepass shader from the PBR implementation like so:

impl Material for CustomMaterial {
  ...

  fn prepass_fragment_shader() -> ShaderRef {
    StandardMaterial::prepass_fragment_shader()
  }
}

[idobenamram]

cool! that makes a lot of sense, @IceSentry figured out the reason! FragmentInput in the default prepass.wgsl was missing
the VERTEX_TANGENT. Fixed it by using VertexOutput instead.

[IceSentry]

This should now be fixed on main after the deferred PR.