Allow unconsumed inputs in fragment shaders #5531
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Imberflur
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Imberflur
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Apr 14, 2024
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Great to see work here! Marking un-draft so it gets added to the review queue |
cwfitzgerald
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cwfitzgerald
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teoxoy
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@Imberflur could you rebase the PR? |
outputs when generating HLSL. Fixes gfx-rs#3748 * Add naga::back::hlsl::FragmentEntryPoint for providing information about the fragment entry point when generating vertex entry points via naga::back::hlsl::Writer::write. Vertex outputs not consumed by the fragment entry point are omitted in the final output struct. * Add naga snapshot test for this new feature, * Remove Features::SHADER_UNUSED_VERTEX_OUTPUT, StageError::InputNotConsumed, and associated validation logic. * Make wgpu dx12 backend pass fragment shader info when generating vertex HLSL. * Add wgpu regression test for allowing unconsumed inputs.
* Add note that nesting structs for the inter-stage interface can't happen. * Remove new TODO notes (some addressed and some transferred to an issue gfx-rs#5577) * Changed issue that regression test refers to 3748 -> 5553 * Add debug_assert that binding.is_some() in hlsl writer * Fix typos caught in CI Also, fix compiling snapshot test when hlsl-out feature is not enabled.
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@teoxoy rebased! |
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By removing them from vertex outputs when generating HLSL.
naga::back::hlsl::FragmentEntryPointfor providing information about the fragment entry point when generating vertex entry points vianaga::back::hlsl::Writer::write. Vertex outputs not consumed by the fragment entry point are omitted in the final output struct.nagasnapshot test for this new feature,Features::SHADER_UNUSED_VERTEX_OUTPUT,StageError::InputNotConsumed, and associated validation logic.Connections
Fixes #3748
Description
My case affected by this is passing in SPIRV from
shadercwhich can optimize out unused inputs from the fragment shader. The shaders are dynamically configured with a pre-processor based on various settings from the user so it can be hard to predict when certain inter-stage variables are unused, and my attempt at configuring out particular outputs from vertex shaders quickly became overly verbose.As noted in the linked issue, this validation was originally in the WebGPU spec but was removed. The validation was necessary for generating HLSL with matching inter-stage interfaces but we can work around that by adjusting the HLSL generation to account for any unconsumed inputs.
After investigating this I found two potential ways to account for this in the generated HLSL:
I went with the second option since it seemed simpler to implement than generating new fields and nicely removed unnecessary work passing unused values (although I assume drivers can probably optimize this out).
Note: This is a breaking change.
Testing
I added a test to for whether the wgpu validation logic now allows unconsumed inputs and a naga snapshot test for removing the unconsumed vertex outputs when generating HLSL.
I have not tested on a windows machine with the dx12 backend!So here are some testing TODOs:cargo xtask teston machine with dx12.Checklist
cargo fmt.cargo clippy. If applicable, add:--target wasm32-unknown-unknown--target wasm32-unknown-emscriptencargo xtask testto run tests.CHANGELOG.md. See simple instructions inside file.