Naga implementation of WebGPU style dual source blending

CHANGELOG.md

@@ -229,7 +229,7 @@ By @brodycj in [#6924](https://github.com/gfx-rs/wgpu/pull/6924).
 #### WebGPU
 
 - Improve efficiency of dropping read-only buffer mappings. By @kpreid in [#7007](https://github.com/gfx-rs/wgpu/pull/7007).
-- `wgpu::Features::DUAL_SOURCE_BLENDING` is now available on WebGPU. By @wumpf in [#????](https://github.com/gfx-rs/wgpu/pull/????).
+- `wgpu::Features::DUAL_SOURCE_BLENDING` is now available on WebGPU. By @wumpf in [#????](https://github.com/gfx-rs/wgpu/pull/????). TODO: not the full story, not a WebGPU thing, it's a Naga/general thing.
 
 ### Performance
 

naga/src/back/glsl/features.rs

@@ -604,15 +604,15 @@ impl<W> Writer<'_, W> {
                     location: _,
                     interpolation,
                     sampling,
-                    second_blend_source,
+                    blend_src,
                 } => {
                     if interpolation == Some(Interpolation::Linear) {
                         self.features.request(Features::NOPERSPECTIVE_QUALIFIER);
                     }
                     if sampling == Some(Sampling::Sample) {
                         self.features.request(Features::SAMPLE_QUALIFIER);
                     }
-                    if second_blend_source {
+                    if blend_src.is_some() {
                         self.features.request(Features::DUAL_SOURCE_BLENDING);
                     }
                 }

naga/src/back/glsl/mod.rs

@@ -455,8 +455,7 @@ impl fmt::Display for VaryingName<'_> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self.binding {
             crate::Binding::Location {
-                second_blend_source: true,
-                ..
+                blend_src: Some(1), ..
             } => {
                 write!(f, "_fs2p_location1",)
             }
@@ -1491,13 +1490,13 @@ impl<'a, W: Write> Writer<'a, W> {
             Some(binding) => binding,
         };
 
-        let (location, interpolation, sampling, second_blend_source) = match *binding {
+        let (location, interpolation, sampling, blend_src) = match *binding {
             crate::Binding::Location {
                 location,
                 interpolation,
                 sampling,
-                second_blend_source,
-            } => (location, interpolation, sampling, second_blend_source),
+                blend_src,
+            } => (location, interpolation, sampling, blend_src),
             crate::Binding::BuiltIn(built_in) => {
                 if let crate::BuiltIn::Position { invariant: true } = built_in {
                     match (self.options.version, self.entry_point.stage) {
@@ -1544,16 +1543,19 @@ impl<'a, W: Write> Writer<'a, W> {
             || !emit_interpolation_and_auxiliary
         {
             if self.options.version.supports_io_locations() {
-                if second_blend_source {
-                    write!(self.out, "layout(location = {location}, index = 1) ")?;
+                if let Some(blend_src) = blend_src {
+                    write!(
+                        self.out,
+                        "layout(location = {location}, index = {blend_src}) "
+                    )?;
                 } else {
                     write!(self.out, "layout(location = {location}) ")?;
                 }
                 None
             } else {
                 Some(VaryingLocation {
                     location,
-                    index: second_blend_source as u32,
+                    index: blend_src.unwrap_or(0),
                 })
             }
         } else {
@@ -1594,7 +1596,7 @@ impl<'a, W: Write> Writer<'a, W> {
                 location,
                 interpolation: None,
                 sampling: None,
-                second_blend_source,
+                blend_src,
             },
             stage: self.entry_point.stage,
             options: VaryingOptions::from_writer_options(self.options, output),

naga/src/back/hlsl/writer.rs

@@ -528,16 +528,11 @@ impl<'a, W: fmt::Write> super::Writer<'a, W> {
                 write!(self.out, " : {builtin_str}")?;
             }
             Some(crate::Binding::Location {
-                second_blend_source: true,
-                ..
+                blend_src: Some(1), ..
             }) => {
                 write!(self.out, " : SV_Target1")?;
             }
-            Some(crate::Binding::Location {
-                location,
-                second_blend_source: false,
-                ..
-            }) => {
+            Some(crate::Binding::Location { location, .. }) => {
                 if stage == Some((ShaderStage::Fragment, Io::Output)) {
                     write!(self.out, " : SV_Target{location}")?;
                 } else {

naga/src/back/msl/mod.rs

@@ -113,7 +113,7 @@ enum ResolvedBinding {
     Attribute(u32),
     Color {
         location: u32,
-        second_blend_source: bool,
+        blend_src: Option<u32>,
     },
     User {
         prefix: &'static str,
@@ -459,18 +459,16 @@ impl Options {
                 location,
                 interpolation,
                 sampling,
-                second_blend_source,
+                blend_src,
             } => match mode {
                 LocationMode::VertexInput => Ok(ResolvedBinding::Attribute(location)),
                 LocationMode::FragmentOutput => {
-                    if second_blend_source && self.lang_version < (1, 2) {
-                        return Err(Error::UnsupportedAttribute(
-                            "second_blend_source".to_string(),
-                        ));
+                    if blend_src.is_some() && self.lang_version < (1, 2) {
+                        return Err(Error::UnsupportedAttribute("blend_src".to_string()));
                     }
                     Ok(ResolvedBinding::Color {
                         location,
-                        second_blend_source,
+                        blend_src,
                     })
                 }
                 LocationMode::VertexOutput | LocationMode::FragmentInput => {
@@ -632,10 +630,10 @@ impl ResolvedBinding {
             Self::Attribute(index) => write!(out, "attribute({index})")?,
             Self::Color {
                 location,
-                second_blend_source,
+                blend_src,
             } => {
-                if second_blend_source {
-                    write!(out, "color({location}) index(1)")?
+                if let Some(blend_src) = blend_src {
+                    write!(out, "color({location}) index({blend_src})")?
                 } else {
                     write!(out, "color({location})")?
                 }

naga/src/back/spv/writer.rs

@@ -1745,7 +1745,7 @@ impl Writer {
                 location,
                 interpolation,
                 sampling,
-                second_blend_source,
+                blend_src,
             } => {
                 self.decorate(id, Decoration::Location, &[location]);
 
@@ -1790,8 +1790,8 @@ impl Writer {
                         }
                     }
                 }
-                if second_blend_source {
-                    self.decorate(id, Decoration::Index, &[1]);
+                if let Some(blend_src) = blend_src {
+                    self.decorate(id, Decoration::Index, &[blend_src]);
                 }
             }
             crate::Binding::BuiltIn(built_in) => {

naga/src/back/wgsl/writer.rs

@@ -18,7 +18,7 @@ enum Attribute {
     Invariant,
     Interpolate(Option<crate::Interpolation>, Option<crate::Sampling>),
     Location(u32),
-    SecondBlendSource,
+    BlendSrc(u32),
     Stage(ShaderStage),
     WorkGroupSize([u32; 3]),
 }
@@ -340,7 +340,7 @@ impl<W: Write> Writer<W> {
         for attribute in attributes {
             match *attribute {
                 Attribute::Location(id) => write!(self.out, "@location({id}) ")?,
-                Attribute::SecondBlendSource => write!(self.out, "@second_blend_source ")?,
+                Attribute::BlendSrc(blend_src) => write!(self.out, "@blend_src({blend_src}) ")?,
                 Attribute::BuiltIn(builtin_attrib) => {
                     let builtin = builtin_str(builtin_attrib)?;
                     write!(self.out, "@builtin({builtin}) ")?;
@@ -2166,7 +2166,7 @@ fn map_binding_to_attribute(binding: &crate::Binding) -> Vec<Attribute> {
             location,
             interpolation,
             sampling,
-            second_blend_source: false,
+            blend_src: None,
         } => vec![
             Attribute::Location(location),
             Attribute::Interpolate(interpolation, sampling),
@@ -2175,10 +2175,10 @@ fn map_binding_to_attribute(binding: &crate::Binding) -> Vec<Attribute> {
             location,
             interpolation,
             sampling,
-            second_blend_source: true,
+            blend_src: Some(blend_src),
         } => vec![
             Attribute::Location(location),
-            Attribute::SecondBlendSource,
+            Attribute::BlendSrc(blend_src),
             Attribute::Interpolate(interpolation, sampling),
         ],
     }

naga/src/front/glsl/functions.rs

@@ -1442,7 +1442,7 @@ impl Context<'_> {
                         location,
                         interpolation,
                         sampling: None,
-                        second_blend_source: false,
+                        blend_src: None,
                     };
                     location += 1;
 
@@ -1478,7 +1478,7 @@ impl Context<'_> {
                                 location,
                                 interpolation,
                                 sampling: None,
-                                second_blend_source: false,
+                                blend_src: None,
                             };
                             location += 1;
                             binding

naga/src/front/glsl/variables.rs

@@ -454,7 +454,7 @@ impl Frontend {
                         location,
                         interpolation,
                         sampling,
-                        second_blend_source: false,
+                        blend_src: None,
                     },
                     handle,
                     storage,

naga/src/front/interpolator.rs

@@ -43,7 +43,7 @@ impl crate::Binding {
             location: _,
             interpolation: ref mut interpolation @ None,
             ref mut sampling,
-            second_blend_source: _,
+            blend_src: _,
         } = *self
         {
             match ty.scalar_kind() {

naga/src/front/spv/mod.rs

@@ -250,7 +250,7 @@ impl Decoration {
                 location,
                 interpolation,
                 sampling,
-                second_blend_source: false,
+                blend_src: None,
             }),
             _ => Err(Error::MissingDecoration(spirv::Decoration::Location)),
         }

naga/src/front/wgsl/lower/mod.rs

@@ -3367,15 +3367,21 @@ impl<'source, 'temp> Lowerer<'source, 'temp> {
             Some(ast::Binding::BuiltIn(b)) => Some(crate::Binding::BuiltIn(b)),
             Some(ast::Binding::Location {
                 location,
-                second_blend_source,
                 interpolation,
                 sampling,
+                blend_src,
             }) => {
+                let blend_src = if let Some(blend_src) = blend_src {
+                    Some(self.const_u32(blend_src, &mut ctx.as_const())?.0)
+                } else {
+                    None
+                };
+
                 let mut binding = crate::Binding::Location {
                     location: self.const_u32(location, &mut ctx.as_const())?.0,
-                    second_blend_source,
                     interpolation,
                     sampling,
+                    blend_src,
                 };
                 binding.apply_default_interpolation(&ctx.module.types[ty].inner);
                 Some(binding)

naga/src/front/wgsl/parse/ast.rs

@@ -142,9 +142,9 @@ pub enum Binding<'a> {
     BuiltIn(crate::BuiltIn),
     Location {
         location: Handle<Expression<'a>>,
-        second_blend_source: bool,
         interpolation: Option<crate::Interpolation>,
         sampling: Option<crate::Sampling>,
+        blend_src: Option<Handle<Expression<'a>>>,
     },
 }
 

naga/src/front/wgsl/parse/directive/enable_extension.rs

@@ -5,24 +5,31 @@ use crate::{front::wgsl::error::Error, Span};
 
 /// Tracks the status of every enable-extension known to Naga.
 #[derive(Clone, Debug, Eq, PartialEq)]
-pub struct EnableExtensions {}
+pub struct EnableExtensions {
+    dual_source_blending: bool,
+}
 
 impl EnableExtensions {
     pub(crate) const fn empty() -> Self {
-        Self {}
+        Self {
+            dual_source_blending: false,
+        }
     }
 
     /// Add an enable-extension to the set requested by a module.
-    #[allow(unreachable_code)]
     pub(crate) fn add(&mut self, ext: ImplementedEnableExtension) {
-        let _field: &mut bool = match ext {};
-        *_field = true;
+        let field: &mut bool = match ext {
+            ImplementedEnableExtension::DualSourceBlending => &mut self.dual_source_blending,
+        };
+        *field = true;
     }
 
     /// Query whether an enable-extension tracked here has been requested.
     #[allow(unused)]
     pub(crate) const fn contains(&self, ext: ImplementedEnableExtension) -> bool {
-        match ext {}
+        match ext {
+            ImplementedEnableExtension::DualSourceBlending => self.dual_source_blending,
+        }
     }
 }
 
@@ -55,7 +62,7 @@ impl EnableExtension {
                 Self::Unimplemented(UnimplementedEnableExtension::ClipDistances)
             }
             Self::DUAL_SOURCE_BLENDING => {
-                Self::Unimplemented(UnimplementedEnableExtension::DualSourceBlending)
+                Self::Implemented(ImplementedEnableExtension::DualSourceBlending)
             }
             _ => return Err(Error::UnknownEnableExtension(span, word)),
         })
@@ -64,19 +71,28 @@ impl EnableExtension {
     /// Maps this [`EnableExtension`] into the sentinel word associated with it in WGSL.
     pub const fn to_ident(self) -> &'static str {
         match self {
-            Self::Implemented(kind) => match kind {},
+            Self::Implemented(kind) => match kind {
+                ImplementedEnableExtension::DualSourceBlending => Self::DUAL_SOURCE_BLENDING,
+            },
+
             Self::Unimplemented(kind) => match kind {
                 UnimplementedEnableExtension::F16 => Self::F16,
                 UnimplementedEnableExtension::ClipDistances => Self::CLIP_DISTANCES,
-                UnimplementedEnableExtension::DualSourceBlending => Self::DUAL_SOURCE_BLENDING,
             },
         }
     }
 }
 
 /// A variant of [`EnableExtension::Implemented`].
 #[derive(Clone, Copy, Debug, Hash, Eq, PartialEq)]
-pub enum ImplementedEnableExtension {}
+pub enum ImplementedEnableExtension {
+    /// Enables the `blend_src` attribute in WGSL.
+    ///
+    /// In the WGSL standard, this corresponds to [`enable dual_source_blending;`].
+    ///
+    /// [`enable dual_source_blending;`]: https://www.w3.org/TR/WGSL/#extension-f16
+    DualSourceBlending,
+}
 
 /// A variant of [`EnableExtension::Unimplemented`].
 #[derive(Clone, Copy, Debug, Hash, Eq, PartialEq)]
@@ -93,20 +109,13 @@ pub enum UnimplementedEnableExtension {
     ///
     /// [`enable clip_distances;`]: https://www.w3.org/TR/WGSL/#extension-f16
     ClipDistances,
-    /// Enables the `blend_src` attribute in WGSL.
-    ///
-    /// In the WGSL standard, this corresponds to [`enable dual_source_blending;`].
-    ///
-    /// [`enable dual_source_blending;`]: https://www.w3.org/TR/WGSL/#extension-f16
-    DualSourceBlending,
 }
 
 impl UnimplementedEnableExtension {
     pub(crate) const fn tracking_issue_num(self) -> u16 {
         match self {
             Self::F16 => 4384,
             Self::ClipDistances => 6236,
-            Self::DualSourceBlending => 6402,
         }
     }
 }