Mesh Shaders Tracking Issue

[inner-daemons]

Replaces #3018.

Spec

Progress

Current open PR(s) and other work

• Naga mesh shader SPIR-V writer #8456
• Naga mesh shader WGSL writer #8481 by @Slightlyclueless
• MSL writer for mesh shaders #8493
• New mesh shader limits #8507

naga

• Add mesh, task shaders to naga shader types so wgpu-hal can stop pretending they are compute shaders - Add mesh shader stages to wgt::ShaderStages and naga::ShaderStage #7292
• Support in WGSL frontend - WGSL parsing for mesh shaders #8370
• Add robust testing of mesh shader related parsing and validation errors #8517
• Validation - New mesh shader limits #8507
• Support in SPIRV writer - Naga mesh shader SPIR-V writer #8456
• Support in HLSL writer - taken on by @luc-rodriguez
• Support in MSL writer - MSL writer for mesh shaders #8493
• Support in WGSL regurgitator - Naga mesh shader WGSL writer #8481
• Support in SPIR-V frontend
• Reflection info for pipeline validation - New mesh shader limits #8507
• Restrict builtins in mesh shader outputs #8360

wgpu-hal backends

• Vulkan - Mesh shaders - initial wgpu hal changes #7089
• DX12 - Mesh Shading for DirectX 12 #7219 ([hal/dx12] Mesh Shaders #8110) - still needs naga support
• Metal - [hal/metal] Mesh Shaders #8139 - naga PR separate

Other

• Formal spec - Added mesh shading spec #7885
• wgpu API - Add mesh shading api to wgpu & wgpu-core #7345
• wgpu-core pipeline validation - Add mesh shading api to wgpu & wgpu-core #7345 (?)
• Limits & validation of mesh and task shader interface in wgpu-core #8003 - New mesh shader limits #8507
• General tests- Add mesh shading api to wgpu & wgpu-core #7345
• More tests - line rendering, limits, etc
• Examples - Add mesh shading api to wgpu & wgpu-core #7345
• Fate of EXPERIMENTAL_MESH_SHADER_MULTIVIEW #8343

Features

• Multiview mesh shaders #7262
• Primitive ID builtin - not supported in wgpu in general yet - Support enable primitive-index; in WGSL #8236 required
• Queries - Mesh shader queries #8523 (unplanned)
• Point primitives(at least in vulkan, probably its own feature)
• Finalize limits - Limits & validation of mesh and task shader interface in wgpu-core #8003 - New mesh shader limits #8507

Current Priorities

• Multiview in wgpu-hal - very simple - Add multiview mesh shaders to wgpu-hal #7278
• Naga types - needed for wgpu-hal completeness(current code pretends they are compute shaders) - Add mesh shader stages to wgt::ShaderStages and naga::ShaderStage #7292
• Formal spec created and added to trunk - Added mesh shading spec #7885
• Experimental wgpu API - blocking many things - Add mesh shading api to wgpu & wgpu-core #7345
• Naga WGSL frontend - needed for proper wgpu implementation - WGSL parsing for mesh shaders #8370
• Naga SPIRV backend - needed for proper wgpu implementation - Naga mesh shader SPIR-V writer #8456
• DX12 in wgpu-hal - desired - [hal/dx12] Mesh Shaders #8110
• Naga reflection info, needed for proper wgpu implementation - New mesh shader limits #8507
• Lots of testing for wgpu - partly in Add mesh shading api to wgpu & wgpu-core #7345

Issues to work out

• How to implement multiview, what features, etc
• Queries

[inner-daemons]

@cwfitzgerald
I’ve been thinking, we probably ought to have some way to indicate the “payload” for task and mesh shaders. I’m updating the original comment to add an attribute, @payload(some global variable). This would also probably mean we don’t need a new storage class. Let me know if you think there is a better option.

[cwfitzgerald]

Sounds fine - one thing to keep in mind that we want the IR to be compatible enough with how SPIR-V does stuff, such that spirv-in can eventually support mesh shaders. I don't know specifics about how mesh shaders work in spirv, but we should be careful to not require things that are too hard to implement in that frrontend. We' already require heroics in the spirv frontend for atomics.

[inner-daemons]

@cwfitzgerald Thanks for the response. I'll try to keep a list of things that might be hard to implement in certain environments.