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Mesh shader HLSL writer #8752

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Mesh shader HLSL writer #8752

inner-daemons wants to merge 105 commits into from
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@inner-daemons inner-daemons commented Dec 17, 2025 •
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Connections
Part of #7197
Closes #7219
Related to #8739
Depends on #8756

Description
Adds support for mesh shaders to HLSL writer. There still exist some things to do:

  • Possibly disable some mesh outputs that are unused in the fragment shader

Testing
Existing tests, snapshots

Squash or Rebase?
Squash

Checklist

  • Run cargo fmt.
  • Run taplo format.
  • Run cargo clippy --tests. If applicable, add:
    • --target wasm32-unknown-unknown
  • Run cargo xtask test to run tests.
  • If this contains user-facing changes, add a CHANGELOG.md entry.

cwfitzgerald and others added 30 commits December 12, 2025 15:48
@cwfitzgerald @inner-daemons
[spv-out] Support for mesh shaders
0622940 
Co-authored-by: Inner Daemons <[email protected]>
@inner-daemons @cwfitzgerald
Update mesh_shader.rs
dc69d86 
Co-authored-by: Connor Fitzgerald <[email protected]>
@inner-daemons
Tried one thing
dfd360f
@inner-daemons
Updated snapshots
c1973fe
@inner-daemons
Tried another thing
50c2aa9
@inner-daemons
Removed per primitive stuff + cull primitive
7749867
@inner-daemons
Testing new thing
ca3f93a
@inner-daemons
Ahh well I think I'm done for the night
4fbfc60
@inner-daemons
Slight improvements
7551f6a
@inner-daemons
Fixed another comment
3225030
@inner-daemons
Added note on feature
c34c474
@inner-daemons
Preparing for merge as is
18164ee
@inner-daemons
Ok I'm tired
0b9bf09
@inner-daemons
Blah blah blah
da72786
@inner-daemons
Updated loop logic
8862d56
@inner-daemons
Tried something else
0286af7
@inner-daemons
Tried another little fix
7cc51c9
@inner-daemons
Tried something new
3818efe
@inner-daemons
Told it to skip instead of expect a failure
ea50cb0
@inner-daemons
Redocumented feature, made tests run on AMD
8d9a451
@inner-daemons
Removed obseleted files, updated changelog, updated shaders
3edc37c
@inner-daemons
Added task shader to the changelog entry
6ffd2d5
@inner-daemons
Enabled debugigng
094a5ac
@inner-daemons
Fixed typo
6417327
@inner-daemons
Trying with better aligned task payload stuff
2e863e2
@inner-daemons
Made the tests actually run on LLVMPIPE
05eada6
@inner-daemons
Testing on LLVMPIPE if removing task payload reads does anything
6dc1fd0
@inner-daemons
Undid test that didnt work
883a443
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Tried making it write a barrier
3457ed5
@inner-daemons
Wrote another barrier I guess
cad1bdf
@cwfitzgerald cwfitzgerald self-assigned this Jan 7, 2026
cwfitzgerald
cwfitzgerald requested changes Jan 15, 2026
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You know, the youzh

naga/tests/out/wgsl/wgsl-mesh-shader.wgsl
Comment on lines +102 to +103
@mesh(mesh_output) @workgroup_size(2, 1, 1)
fn ms_divergent(@builtin(local_invocation_id) thread_id_1: vec3<u32>) {
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Why was this changed?

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@inner-daemons inner-daemons Jan 15, 2026

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Our HLSL writer has a bug where it doesn't consider the local_invocation_index being written by the zero-initializer/mesh shader output loop to be a builtin. So I had to use an alternative here, since local_invocation_index was being used elsewhere

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Is there a bug about this somewhere?

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inner-daemons commented Jan 16, 2026 •
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@cwfitzgerald One question here, not probably too important:

Can you explain to me whats going on in naga::back::hlsl::Writer::write_ep_output_struct? It seems to be removing some HLSL outputs but as far as I can tell DX12 allows the vertex shader to output @location things unused by the fragment shader. I'm not sure if I should be doing this in the mesh shader writer.

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Mesh Shading for DirectX 12

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