feat: implement F16 support in shaders (#5701)

Co-authored-by: FL33TW00D <[email protected]>
Co-authored-by: Connor Fitzgerald <[email protected]>
Co-authored-by: ErichDonGubler <[email protected]>

Author: 3 people

Cargo.lock

@@ -108,6 +108,7 @@ fern = "0.7"
 flume = "0.11"
 futures-lite = "2"
 glam = "0.29"
+half = "2.5" # We require 2.5 to have `Arbitrary` support.
 hashbrown = { version = "0.14.5", default-features = false, features = [
     "ahash",
     "inline-more",

Cargo.toml

@@ -41,10 +41,17 @@ msl-out = []
 ## If you want to enable MSL output it regardless of the target platform, use `naga/msl-out`.
 msl-out-if-target-apple = []
 
-serialize = ["dep:serde", "bitflags/serde", "hashbrown/serde", "indexmap/serde"]
+serialize = [
+    "dep:serde",
+    "bitflags/serde",
+    "half/serde",
+    "hashbrown/serde",
+    "indexmap/serde",
+]
 deserialize = [
     "dep:serde",
     "bitflags/serde",
+    "half/serde",
     "hashbrown/serde",
     "indexmap/serde",
 ]
@@ -84,9 +91,12 @@ termcolor = { version = "1.4.1" }
 # https://github.com/brendanzab/codespan/commit/e99c867339a877731437e7ee6a903a3d03b5439e
 codespan-reporting = { version = "0.11.0" }
 hashbrown.workspace = true
+half = { workspace = true, features = ["arbitrary", "num-traits"] }
 rustc-hash.workspace = true
 indexmap.workspace = true
 log = "0.4"
+# `half` requires 0.2.16 for `FromBytes` and `ToBytes`.
+num-traits = "0.2.16"
 strum = { workspace = true, optional = true }
 spirv = { version = "0.3", optional = true }
 thiserror.workspace = true

naga/Cargo.toml

@@ -2703,6 +2703,9 @@ impl<'a, W: Write> Writer<'a, W> {
                     // decimal part even it's zero which is needed for a valid glsl float constant
                     crate::Literal::F64(value) => write!(self.out, "{value:?}LF")?,
                     crate::Literal::F32(value) => write!(self.out, "{value:?}")?,
+                    crate::Literal::F16(_) => {
+                        return Err(Error::Custom("GLSL has no 16-bit float type".into()));
+                    }
                     // Unsigned integers need a `u` at the end
                     //
                     // While `core` doesn't necessarily need it, it's allowed and since `es` needs it we

naga/src/back/glsl/mod.rs

@@ -2628,6 +2628,7 @@ impl<'a, W: fmt::Write> super::Writer<'a, W> {
                 // decimal part even it's zero
                 crate::Literal::F64(value) => write!(self.out, "{value:?}L")?,
                 crate::Literal::F32(value) => write!(self.out, "{value:?}")?,
+                crate::Literal::F16(value) => write!(self.out, "{value:?}h")?,
                 crate::Literal::U32(value) => write!(self.out, "{value}u")?,
                 // HLSL has no suffix for explicit i32 literals, but not using any suffix
                 // makes the type ambiguous which prevents overload resolution from

naga/src/back/hlsl/writer.rs

@@ -8,6 +8,9 @@ use core::{
     fmt::{Display, Error as FmtError, Formatter, Write},
     iter,
 };
+use num_traits::real::Real as _;
+
+use half::f16;
 
 use super::{sampler as sm, Error, LocationMode, Options, PipelineOptions, TranslationInfo};
 use crate::{
@@ -182,9 +185,11 @@ impl Display for TypeContext<'_> {
                 write!(out, "{}::atomic_{}", NAMESPACE, scalar.to_msl_name())
             }
             crate::TypeInner::Vector { size, scalar } => put_numeric_type(out, scalar, &[size]),
-            crate::TypeInner::Matrix { columns, rows, .. } => {
-                put_numeric_type(out, crate::Scalar::F32, &[rows, columns])
-            }
+            crate::TypeInner::Matrix {
+                columns,
+                rows,
+                scalar,
+            } => put_numeric_type(out, scalar, &[rows, columns]),
             crate::TypeInner::Pointer { base, space } => {
                 let sub = Self {
                     handle: base,
@@ -425,8 +430,12 @@ impl crate::Scalar {
         match self {
             Self {
                 kind: Sk::Float,
-                width: _,
+                width: 4,
             } => "float",
+            Self {
+                kind: Sk::Float,
+                width: 2,
+            } => "half",
             Self {
                 kind: Sk::Sint,
                 width: 4,
@@ -483,7 +492,7 @@ fn should_pack_struct_member(
     match *ty_inner {
         crate::TypeInner::Vector {
             size: crate::VectorSize::Tri,
-            scalar: scalar @ crate::Scalar { width: 4, .. },
+            scalar: scalar @ crate::Scalar { width: 4 | 2, .. },
         } if is_tight => Some(scalar),
         _ => None,
     }
@@ -1459,6 +1468,21 @@ impl<W: Write> Writer<W> {
                 crate::Literal::F64(_) => {
                     return Err(Error::CapabilityNotSupported(valid::Capabilities::FLOAT64))
                 }
+                crate::Literal::F16(value) => {
+                    if value.is_infinite() {
+                        let sign = if value.is_sign_negative() { "-" } else { "" };
+                        write!(self.out, "{sign}INFINITY")?;
+                    } else if value.is_nan() {
+                        write!(self.out, "NAN")?;
+                    } else {
+                        let suffix = if value.fract() == f16::from_f32(0.0) {
+                            ".0h"
+                        } else {
+                            "h"
+                        };
+                        write!(self.out, "{value}{suffix}")?;
+                    }
+                }
                 crate::Literal::F32(value) => {
                     if value.is_infinite() {
                         let sign = if value.is_sign_negative() { "-" } else { "" };