Shader compilation error with `webgpu` only in debug builds

[rparrett]

Bevy version

0.16.0-rc.1, most recent main

Relevant system information

macOS (m4), Chrome

What you did

Build and run Bevy's 3d_scene example for webgpu, as described in the docs.

Except, do a debug build instead of a release build.

cargo build --features webgpu --target wasm32-unknown-unknown --example 3d_scene 
wasm-bindgen --out-name wasm_example \
    --out-dir examples/wasm/target \
    --target web target/wasm32-unknown-unknown/debug/examples/3d_scene.wasm
basic-http-server examples/wasm/

What went wrong

Scene fails to render, with multiple runtime errors similar to

ERROR /Users/me/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/bevy_render-0.16.0-rc.1/src/render_resource/pipeline_cache.rs:1010 failed to process shader:
error: failed to build a valid final module: Global variable [12] 'push_constants' is invalid        ┌─ /Users/me/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/bevy_pbr-0.16.0-rc.1/src/render/mesh_preprocess.wgsl:120:1
    │
120 │ var<push_constant> push_constants: PushConstants;
    │ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ naga::GlobalVariable [12]
    │
    = Capability Capabilities(PUSH_CONSTANT) is not supported

Additional information

Release builds "work."

cargo build --features webgpu --target wasm32-unknown-unknown --example 3d_scene --release
wasm-bindgen --out-name wasm_example \
    --out-dir examples/wasm/target \
    --target web target/wasm32-unknown-unknown/release/examples/3d_scene.wasm
basic-http-server examples/wasm/

But they show warnings like:

Compilation log for [Invalid ShaderModule (unlabeled)]:
1 error(s) generated while compiling the shader:
:33:1 error: use of variable address space 'push_constant' requires enabling extension 'chromium_experimental_push_constant'
var<push_constant> constants: Constants;
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

127.0.0.1/:1 The number of storage textures (12) in the Compute stage exceeds the maximum per-stage limit (8).
 - While validating binding counts
 - While validating [BindGroupLayoutDescriptor ""downsample depth bind group layout""]
 - While calling [Device].CreateBindGroupLayout([BindGroupLayoutDescriptor ""downsample depth bind group layout""]).

[JMS55]

Push constants need to be gated behind ifdefs on webgpu.

[greeble-dev]

I poked around this but didn't find a good solution. Adding some notes in case they're useful.

I guessed that there are two approaches:

1. The occlusion culling shader should avoid using push constants, or have an alternative method if push constants are not supported.
2. The occlusion culling feature should be disabled if push constants are not supported.

I only looked at the second approach.

Most of the occlusion culling is disabled by default and only enabled if the camera has a OcclusionCulling component. However, parts of the pipeline are set up regardless - see PreprocessPipelines::early_gpu_occlusion_culling_preprocess and a few other pipelines containing gpu_occlusion. I suspect this is what triggers the shader compile errors, but I couldn't quite nail that down.

I tried disabling these pipelines by setting GpuPreprocessingSupport::max_supported_mode to GpuPreprocessingMode::None (previously it was set to PreprocessingOnly). This was enough to get 3d_scene working, but I don't think it's the right solution as it disables more than just occlusion culling. Maybe it's a fallback if a better fix isn't ready for 0.16.

I suspect a better solution is for PreprocessPipelines::early_gpu_occlusion_culling_preprocess and company to only be set up if GpuPreprocessingSupport::max_supported_mode is GpuPreprocessingMode::Culling. But this needs quite a few changes and I've run out of time for now.

[rparrett]

The scene now renders, but (fewer?) errors/warnings are still logged.

ERROR crates/bevy_render/src/render_resource/pipeline_cache.rs:1010 failed to process shader:error: failed to build a valid final module: Global variable [14] 'constants' is invalid
   ┌─ crates/bevy_core_pipeline/src/experimental/mip_generation/downsample_depth.wgsl:28:1
   │
28 │ var<push_constant> constants: Constants;
   │ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ naga::GlobalVariable [14]
   │   = Capability Capabilities(PUSH_CONSTANT) is not supported

The number of storage textures (12) in the Compute stage exceeds the maximum per-stage limit (8).
 - While validating binding counts
 - While validating [BindGroupLayoutDescriptor ""downsample depth bind group layout""]
 - While calling [Device].CreateBindGroupLayout([BindGroupLayoutDescriptor ""downsample depth bind group layout""]).

The number of storage textures (12) in the Compute stage exceeds the maximum per-stage limit (8).
 - While validating binding counts
 - While validating [BindGroupLayoutDescriptor ""downsample multisample depth bind group layout""]
 - While calling [Device].CreateBindGroupLayout([BindGroupLayoutDescriptor ""downsample multisample depth bind group layout""]).

Tested cbc023b and rc.3