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Don't declare atomics in the read-only late mesh preprocessing buffer#24650

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Don't declare atomics in the read-only late mesh preprocessing buffer#24650
stuartparmenter wants to merge 1 commit into
bevyengine:mainfrom
stuartparmenter:late-preprocess-readonly-atomics

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@stuartparmenter

@stuartparmenter stuartparmenter commented Jun 17, 2026

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Objective

  • Most examples in Bevy w/ wgpu main break on DX12 because Naga now (correctly) rejects atomicLoad when bound read only (by incorrectly generating bad code... going to work on a naga fix to more cleanly reject). See https://www.w3.org/TR/WGSL/#atomic-load that it is for read_write.

Solution

  • Use non-atomic in the same spot for LATE_PHASE.

Testing

  • Change Bevy to use latest wgpu main, run most examples w/ WGPU_BACKEND="dx12"

@kfc35 kfc35 added C-Bug An unexpected or incorrect behavior A-Rendering Drawing game state to the screen O-DX12 Specific to the DX12 render API D-Straightforward Simple bug fixes and API improvements, docs, test and examples S-Needs-Review Needs reviewer attention (from anyone!) to move forward D-Shaders This code uses GPU shader languages labels Jun 17, 2026
@github-project-automation github-project-automation Bot moved this to Needs SME Triage in Rendering Jun 17, 2026
beicause
beicause approved these changes Jun 18, 2026
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Looks correct.

I'm not sure why this is dx12-specific. It should fail on other backends too if wgsl spec disallows it.

@stuartparmenter

stuartparmenter commented Jun 18, 2026 •
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Thanks!

It broke because of gfx-rs/wgpu#9387 which, which only changed some of the code generation. It doesn't currently reject, but rather generates bad code that then fails. I asked the wgpu folks and after checking the specs making it reject across the board seems like the right fix upstream, so am planning on trying to do that when I get a chance.

kfc35
kfc35 approved these changes Jun 18, 2026
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looks correct to me

@kfc35 kfc35 added S-Ready-For-Final-Review This PR has been approved by the community. It's ready for a maintainer to consider merging it and removed S-Needs-Review Needs reviewer attention (from anyone!) to move forward labels Jun 18, 2026
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A-Rendering Drawing game state to the screen C-Bug An unexpected or incorrect behavior D-Shaders This code uses GPU shader languages D-Straightforward Simple bug fixes and API improvements, docs, test and examples O-DX12 Specific to the DX12 render API S-Ready-For-Final-Review This PR has been approved by the community. It's ready for a maintainer to consider merging it

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Status: Needs SME Triage

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