Mesh shader HLSL writer by inner-daemons · Pull Request #8752 · gfx-rs/wgpu

inner-daemons · 2025-12-17T22:20:48Z

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.

Co-authored-by: Inner Daemons <magnus.larsson.mn@gmail.com>

Co-authored-by: Connor Fitzgerald <connorwadefitzgerald@gmail.com>

* Initial commit adding miscellaneous changes from msl-write and hlsl-write * Same as previous commit * Fixed divergence issue * Removed some unnecessary barriers * Zero init workgroup memory * Added limits validation * Added changelog * Handled overflow, removed todo * Lets see if this fixes llvmpipe * Also this commit fixes llvmpipe maybe * Unfortunate but not too unexpected at this point * Updated feature to say to use ShaderRuntimeChecks::unchecked() * Updated snapshots and took some changes from the hlsl writer * Snapshots * 2 quick tweaks * Updated framework with suggestions by Connor in #8752 * Moved the task runtime limits into naga::back * Fixed soem stuff * Fixed checks: >= into > * Cant believe I forgot this * Removed code using u64 to check stuff * Removed thing with limiting it to 2<<21 * Some more work * Fixed compiles * Added new field to spv options * Updated some stuff to pass around the task runtime limits in more ways * New PR started * Did another quick fix * Another quick fix * Added changelog entry * Added some explanation docs * Fixed a warning * Fixed shader * Fixed some things & added docs * Reverted dxc thing * Fixed thing * Refactored to TaskDispatchLimits * Fixed compile error

…write-id

Wumpf

still needs some final touches!

CHANGELOG.md

examples/features/src/framework.rs

naga/src/back/hlsl/mod.rs

naga/src/back/hlsl/conv.rs

naga/src/back/hlsl/writer.rs

naga/src/back/hlsl/mesh_shader.rs

inner-daemons · 2026-02-22T18:12:30Z

@Wumpf Ok I'll address these soon-ish, plus I'll fix up the MSL writer PR which probably has many of the same problems. Thanks for the quick review!

…write-id

Co-authored-by: Andreas Reich <r_andreas2@web.de>

inner-daemons · 2026-02-22T19:04:25Z

@Wumpf Comments addressed

inner-daemons · 2026-02-22T19:18:44Z

@Wumpf I believe this will expose an issue that will impact Firefox significantly, so don't merge it until that's fixed. Same goes for the MSL PR (though I'm not sure its as singificant in MSL).

inner-daemons · 2026-02-23T18:39:08Z

Alright lets block this on #9099

…write-id

Wumpf

nice, thanks for addressing all these

Wumpf · 2026-03-01T17:41:13Z

docs/api-specs/mesh_shading.md

 > **NOTE**: More limits will be added when support is added to `naga`.

-* `Limits::max_task_workgroup_total_count` - the maximum total number of workgroups from a `draw_mesh_tasks` command or similar. The dimensions passed must be less than or equal to this limit when multiplied together.
-* `Limits::max_task_workgroups_per_dimension` - the maximum for each of the 3 workgroup dimensions in a `draw_mesh_tasks` command. Each dimension passed must be less than or equal to this limit.
-* `max_mesh_multiview_count` - The maximum number of views used when multiview rendering with a mesh shader pipeline.
+* `Limits::max_task_mesh_workgroup_total_count` - the maximum total number of workgroups from a `draw_mesh_tasks` command or similar. The dimensions passed must be less than or equal to this limit when multiplied together.
+* `Limits::max_task_mesh_workgroups_per_dimension` - the maximum for each of the 3 workgroup dimensions in a `draw_mesh_tasks` command. Each dimension passed must be less than or equal to this limit.
+* `max_task_invocations_per_workgroup` - The maximum total number of threads in a task shader workgroup, given by `workgroupSize.x * workgroupSize.y * workgroupSize.z`.
+* `max_task_invocations_per_dimension` the maximum value for each of `workgroupSize.x`, `workgroupSize.y` and `workgroupSize.z` in task shader workgroups.
+* `max_mesh_invocations_per_workgroup` - The maximum total number of threads in a mesh shader workgroup, given by `workgroupSize.x * workgroupSize.y * workgroupSize.z`.
+* `max_mesh_invocations_per_dimension` the maximum value for each of `workgroupSize.x`, `workgroupSize.y` and `workgroupSize.z` in mesh shader workgroups.
+* `max_task_payload_size` - the size of an `var<task_payload>` variable, in bytes.
+* `max_mesh_output_vertices` - the maximum number of vertices that a single mesh shader workgroup may output.
+* `max_mesh_output_primitives` - the maximum number of primitives that a single mesh shader workgroup may output.
+* `max_mesh_multiview_count` - the maximum number of views used when multiview rendering with a mesh shader pipeline.


nice! But I suppose the "more limits will be added" bit is obsolete now?

So the MSL writer PR adds 1 more limit, once we get this merged and I handle the changes from this in the MSL PR then we can remove that.

cwfitzgerald and others added 30 commits December 12, 2025 15:48

[spv-out] Support for mesh shaders

0622940

Co-authored-by: Inner Daemons <magnus.larsson.mn@gmail.com>

Update mesh_shader.rs

dc69d86

Co-authored-by: Connor Fitzgerald <connorwadefitzgerald@gmail.com>

Tried one thing

dfd360f

Updated snapshots

c1973fe

Tried another thing

50c2aa9

Removed per primitive stuff + cull primitive

7749867

Testing new thing

ca3f93a

Ahh well I think I'm done for the night

4fbfc60

Slight improvements

7551f6a

Fixed another comment

3225030

Added note on feature

c34c474

Preparing for merge as is

18164ee

Ok I'm tired

0b9bf09

Blah blah blah

da72786

Updated loop logic

8862d56

Tried something else

0286af7

Tried another little fix

7cc51c9

Tried something new

3818efe

Told it to skip instead of expect a failure

ea50cb0

Redocumented feature, made tests run on AMD

8d9a451

Removed obseleted files, updated changelog, updated shaders

3edc37c

Added task shader to the changelog entry

6ffd2d5

Enabled debugigng

094a5ac

Fixed typo

6417327

Trying with better aligned task payload stuff

2e863e2

Made the tests actually run on LLVMPIPE

05eada6

Testing on LLVMPIPE if removing task payload reads does anything

6dc1fd0

Undid test that didnt work

883a443

Tried making it write a barrier

3457ed5

Wrote another barrier I guess

cad1bdf

inner-daemons added 5 commits January 31, 2026 02:14

Updated some stuff to pass around the task runtime limits in more ways

c8df89b

Merge branch 'mesh-shading/spv-fixes' into mesh-shading/hlsl-write-id

afe4267

Added new option to hlsl writer

f4f4140

Fixed an issue and removed some unnecessary config

e88652b

Tried to fix another compile error

ebeeda1

inner-daemons added 3 commits February 16, 2026 14:26

Merge remote-tracking branch 'upstream/trunk' into mesh-shading/hlsl-…

e64067a

…write-id

Tried to fix some stuff

1398c61

Updated snapshots

2c0eb59

cwfitzgerald assigned Wumpf Feb 18, 2026

Merge branch 'trunk' into mesh-shading/hlsl-write-id

dd08f38

Wumpf self-requested a review February 21, 2026 20:09

Wumpf requested changes Feb 22, 2026

View reviewed changes

inner-daemons and others added 8 commits February 22, 2026 12:22

Merge remote-tracking branch 'upstream/trunk' into mesh-shading/hlsl-…

29bdebf

…write-id

Various quick changes

ff5a2fc

Update naga/src/back/hlsl/writer.rs

8c95e72

Co-authored-by: Andreas Reich <r_andreas2@web.de>

Update naga/src/back/hlsl/mesh_shader.rs

2fbfbc0

Co-authored-by: Andreas Reich <r_andreas2@web.de>

Fixed recommendations and updated snapshots

1622bb1

Updated the spec

073286a

Fixed another small commet

277a042

Split up mesh shader funciton

7e1fc43

inner-daemons requested a review from Wumpf February 22, 2026 19:04

inner-daemons mentioned this pull request Feb 23, 2026

Fix local_invocation_id and local_invocation_index handling #9099

Open

6 tasks

inner-daemons added 2 commits February 27, 2026 15:09

Merge remote-tracking branch 'upstream/trunk' into mesh-shading/hlsl-…

c7a42a2

…write-id

Fixed thing

aefa1f8

Wumpf approved these changes Mar 1, 2026

View reviewed changes

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