feat: implement F16 support in shaders

[FL33TW00D]

Connections

• Hard dependency on WGSL: Add a skeleton for enable-extensions/enable …; that reports nice errors #6424.
• Resolves WGSL: Support the enable directive #5476.
• Resolves [meta] f16 support #4384.

Checklist for merge-ability

• Test multiple redundant directives (I think there may be a cleaner way to do this: https://github.com/gfx-rs/wgpu/pull/5701/files#diff-9ef835ffc5f7d7313243db5bfa371d3115b82c0705d4f1df75c98dfe07d927a1R2175)
• MSL out
• HLSL out
• SPV out
• Arbitrary for F16 on half-rs: feature: Arbitrary starkat99/half-rs#111. Currently we are using a git dep on my fork which is causing CI to fail.
• hexf_parse f16 support: https://github.com/lifthrasiir/hexf. This one won't be fun. Did some work on it here: lifthrasiir/hexf@master...FL33TW00D:hexf:feature/f16 . Deferred to Implement Parsing of Hexadecimal F16 #7046
• We should make sure that we are properly validating As casts of matrices, because that code currently assumes that all matrices have the same kind (Naga's typechecker ignores scalar kind when casting matrices #6441).

Additional context

F16 is available in >=SM6.2: https://github.com/microsoft/DirectXShaderCompiler/wiki/16-Bit-Scalar-Types

[FL33TW00D]

I've marked this as ready for review, as the wgpu specific logic is implemented and would be great to start iterating on it.

2 main blockers are:

1. Merging of the PR on half-rs.
2. hexf-parse improved implementation.

[FL33TW00D]

Dogfooding works! Fixed a few bugs in 30e12b5. Still waiting on upstream.

[teoxoy]

One thing I'm concerned is that the polyfills we have in some of the backends might not support f16. It would be worth adding more tests covering the built-in functions and operations that support f16. Execution tests would be great as well, they live in tests/tests/shader.

[jimblandy]

We should make sure that we are properly validating As casts of matrices, because that code currently assumes that all matrices have the same kind (#6441).

[raphamorim]

Super awesome work folks, really appreciate it!! 👏 <3
@FL33TW00D please lemme know if I can help in anything 🙏

[wpmed92]

Is there an ETA for this to ship? We'd like to support f16 in tinygrad, we love wgpu, but are considering switching to dawn if it's not expected to ship in the near future.

[raphamorim]

Is there an ETA for this to ship? We'd like to support f16 in tinygrad, we love wgpu, but are considering switching to dawn if it's not expected to ship in the near future.

same, i love wgpu and use on rio terminal. Please lemme know if I can help any way to ship this feature. Maybe can split some work

[FL33TW00D]

@wpmed92 @raphamorim

If either of you are using Vulkan or Windows backend, feel free to start testing support for F16 using this branch.

I use the Metal backend, implemented enough support so that all my own tests pass.

[raphamorim]

Sounds good @FL33TW00D , i actually started testing this branch in Rio already.

Regarding starkat99/half-rs#111 I have been thinking in publish a fork to crates io and maintain until your PR get merged

[raphamorim]

Done: https://crates.io/crates/half-2
Hope unblock the CI issue for now, once your PR is merged then need to move back to half

[raphamorim]

@FL33TW00D created a PR raphamorim/rio#875 but having trouble with naga validation

    Finished `dev` profile [unoptimized + debuginfo] target(s) in 13.61s
     Running `target/debug/rio`
thread 'main' panicked at /Users/rapha/.cargo/git/checkouts/wgpu-48a004a2060e66f4/bfad205/wgpu/src/backend/wgpu_core.rs:3413:5:
wgpu error: Validation Error

Caused by:
  In Device::create_shader_module

Shader '' parsing error: expected global item ('struct', 'const', 'var', 'alias', ';', 'fn') or the end of the file, found 'enable'
  ┌─ wgsl:1:1
  │
1 │ enable f16;
  │ ^^^^^^ expected global item ('struct', 'const', 'var', 'alias', ';', 'fn') or the end of the file


      expected global item ('struct', 'const', 'var', 'alias', ';', 'fn') or the end of the file, found 'enable'

[FL33TW00D]

@FL33TW00D created a PR raphamorim/rio#875 but having trouble with naga validation

    Finished `dev` profile [unoptimized + debuginfo] target(s) in 13.61s
     Running `target/debug/rio`
thread 'main' panicked at /Users/rapha/.cargo/git/checkouts/wgpu-48a004a2060e66f4/bfad205/wgpu/src/backend/wgpu_core.rs:3413:5:
wgpu error: Validation Error

Caused by:
  In Device::create_shader_module

Shader '' parsing error: expected global item ('struct', 'const', 'var', 'alias', ';', 'fn') or the end of the file, found 'enable'
  ┌─ wgsl:1:1
  │
1 │ enable f16;
  │ ^^^^^^ expected global item ('struct', 'const', 'var', 'alias', ';', 'fn') or the end of the file


      expected global item ('struct', 'const', 'var', 'alias', ';', 'fn') or the end of the file, found 'enable'

Just checked out 808db24 and ran:
RUST_LOG=shader_f16 cargo run --bin wgpu-examples shader-f16
It works correctly.

You forgot to specify the branch in the cargo git dep!

[raphamorim]

You forgot to specify the branch in the cargo git dep!

You are indeed correct, thank you!

[cwfitzgerald]

Getting this over the line is on my list, will probably be next week.

[ErichDonGubler]

I've resolved conflicts with the latest examples/ changes (I think, spot check me @cwfitzgerald), and added a fixup! that tentatively consumes @raphamorim's half-2 crate.

[cwfitzgerald]

I have split the hex parsing task into a different work item to follow this. See #7046.