Implement shader barycentrics

atlv24 · atlv24 · commit b853dc54250a · 2025-10-11T00:28:34.000-04:00
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -73,6 +73,12 @@ SamplerDescriptor {
 }
 ```
 
+### Added/New Features
+
+## General
+
+- Implement shader triangle barycentric coordinate builtins. By @atlv24 in [#8320](https://github.com/gfx-rs/wgpu/pull/8320).
+
 ### Bug Fixes
 
 #### General
diff --git a/naga/src/back/glsl/mod.rs b/naga/src/back/glsl/mod.rs
@@ -5227,6 +5227,7 @@ const fn glsl_built_in(built_in: crate::BuiltIn, options: VaryingOptions) -> &'s
         Bi::PointCoord => "gl_PointCoord",
         Bi::FrontFacing => "gl_FrontFacing",
         Bi::PrimitiveIndex => "uint(gl_PrimitiveID)",
+        Bi::Barycentric => "gl_BaryCoordEXT",
         Bi::SampleIndex => "gl_SampleID",
         Bi::SampleMask => {
             if options.output {
diff --git a/naga/src/back/hlsl/conv.rs b/naga/src/back/hlsl/conv.rs
@@ -161,6 +161,7 @@ impl crate::BuiltIn {
             Self::FragDepth => "SV_Depth",
             Self::FrontFacing => "SV_IsFrontFace",
             Self::PrimitiveIndex => "SV_PrimitiveID",
+            Self::Barycentric => "SV_Barycentrics",
             Self::SampleIndex => "SV_SampleIndex",
             Self::SampleMask => "SV_Coverage",
             // compute
diff --git a/naga/src/back/msl/mod.rs b/naga/src/back/msl/mod.rs
@@ -530,6 +530,11 @@ impl Options {
                     crate::BuiltIn::PrimitiveIndex if self.lang_version < (2, 2) => {
                         return Err(Error::UnsupportedAttribute("primitive_id".to_string()));
                     }
+                    // macOS: Since Metal 2.2
+                    // iOS: Since Metal 2.3 (check depends on https://github.com/gfx-rs/naga/issues/2164)
+                    crate::BuiltIn::Barycentric if self.lang_version < (2, 2) => {
+                        return Err(Error::UnsupportedAttribute("barycentric_coord".to_string()));
+                    }
                     _ => {}
                 }
 
@@ -680,6 +685,7 @@ impl ResolvedBinding {
                     Bi::PointCoord => "point_coord",
                     Bi::FrontFacing => "front_facing",
                     Bi::PrimitiveIndex => "primitive_id",
+                    Bi::Barycentric => "barycentric_coord",
                     Bi::SampleIndex => "sample_id",
                     Bi::SampleMask => "sample_mask",
                     // compute
diff --git a/naga/src/back/spv/writer.rs b/naga/src/back/spv/writer.rs
@@ -2089,6 +2089,13 @@ impl Writer {
                         )?;
                         BuiltIn::PrimitiveId
                     }
+                    Bi::Barycentric => {
+                        self.require_any(
+                            "`barycentric` built-in",
+                            &[spirv::Capability::FragmentBarycentricKHR],
+                        )?;
+                        BuiltIn::BaryCoordKHR
+                    }
                     Bi::SampleIndex => {
                         self.require_any(
                             "`sample_index` built-in",
diff --git a/naga/src/common/wgsl/to_wgsl.rs b/naga/src/common/wgsl/to_wgsl.rs
@@ -169,6 +169,7 @@ impl TryToWgsl for crate::BuiltIn {
             Bi::FragDepth => "frag_depth",
             Bi::FrontFacing => "front_facing",
             Bi::PrimitiveIndex => "primitive_index",
+            Bi::Barycentric => "barycentric",
             Bi::SampleIndex => "sample_index",
             Bi::SampleMask => "sample_mask",
             Bi::GlobalInvocationId => "global_invocation_id",
diff --git a/naga/src/front/glsl/variables.rs b/naga/src/front/glsl/variables.rs
@@ -200,6 +200,7 @@ impl Frontend {
                     "gl_BaseVertex" => BuiltIn::BaseVertex,
                     "gl_BaseInstance" => BuiltIn::BaseInstance,
                     "gl_PrimitiveID" => BuiltIn::PrimitiveIndex,
+                    "gl_BaryCoordEXT" => BuiltIn::Barycentric,
                     "gl_InstanceIndex" => BuiltIn::InstanceIndex,
                     "gl_VertexIndex" => BuiltIn::VertexIndex,
                     "gl_SampleID" => BuiltIn::SampleIndex,
diff --git a/naga/src/front/spv/convert.rs b/naga/src/front/spv/convert.rs
@@ -147,6 +147,7 @@ pub(super) fn map_builtin(word: spirv::Word, invariant: bool) -> Result<crate::B
         Some(Bi::PointCoord) => crate::BuiltIn::PointCoord,
         Some(Bi::FrontFacing) => crate::BuiltIn::FrontFacing,
         Some(Bi::PrimitiveId) => crate::BuiltIn::PrimitiveIndex,
+        Some(Bi::BaryCoordKHR) => crate::BuiltIn::Barycentric,
         Some(Bi::SampleId) => crate::BuiltIn::SampleIndex,
         Some(Bi::SampleMask) => crate::BuiltIn::SampleMask,
         // compute
diff --git a/naga/src/front/spv/mod.rs b/naga/src/front/spv/mod.rs
@@ -6038,6 +6038,10 @@ impl<I: Iterator<Item = u32>> Frontend<I> {
                             size: crate::VectorSize::Tri,
                             scalar: crate::Scalar::U32,
                         }),
+                        crate::BuiltIn::Barycentric => Some(crate::TypeInner::Vector {
+                            size: crate::VectorSize::Tri,
+                            scalar: crate::Scalar::F32,
+                        }),
                         _ => None,
                     };
                     if let (Some(inner), Some(crate::ScalarKind::Sint)) =
diff --git a/naga/src/front/wgsl/parse/conv.rs b/naga/src/front/wgsl/parse/conv.rs
@@ -36,6 +36,7 @@ pub fn map_built_in(
         "front_facing" => crate::BuiltIn::FrontFacing,
         "frag_depth" => crate::BuiltIn::FragDepth,
         "primitive_index" => crate::BuiltIn::PrimitiveIndex,
+        "barycentric" => crate::BuiltIn::Barycentric,
         "sample_index" => crate::BuiltIn::SampleIndex,
         "sample_mask" => crate::BuiltIn::SampleMask,
         // compute
diff --git a/naga/src/ir/mod.rs b/naga/src/ir/mod.rs
@@ -387,6 +387,7 @@ pub enum BuiltIn {
     PointCoord,
     FrontFacing,
     PrimitiveIndex,
+    Barycentric,
     SampleIndex,
     SampleMask,
     // compute
diff --git a/naga/src/valid/interface.rs b/naga/src/valid/interface.rs
@@ -180,6 +180,7 @@ impl VaryingContext<'_> {
                     Bi::ClipDistance => Capabilities::CLIP_DISTANCE,
                     Bi::CullDistance => Capabilities::CULL_DISTANCE,
                     Bi::PrimitiveIndex => Capabilities::PRIMITIVE_INDEX,
+                    Bi::Barycentric => Capabilities::SHADER_BARYCENTRICS,
                     Bi::ViewIndex => Capabilities::MULTIVIEW,
                     Bi::SampleIndex => Capabilities::MULTISAMPLED_SHADING,
                     Bi::NumSubgroups
@@ -267,6 +268,14 @@ impl VaryingContext<'_> {
                         self.stage == St::Fragment && !self.output,
                         *ty_inner == Ti::Scalar(crate::Scalar::U32),
                     ),
+                    Bi::Barycentric => (
+                        self.stage == St::Fragment && !self.output,
+                        *ty_inner
+                            == Ti::Vector {
+                                size: Vs::Tri,
+                                scalar: crate::Scalar::F32,
+                            },
+                    ),
                     Bi::SampleIndex => (
                         self.stage == St::Fragment && !self.output,
                         *ty_inner == Ti::Scalar(crate::Scalar::U32),
diff --git a/naga/src/valid/mod.rs b/naga/src/valid/mod.rs
@@ -186,6 +186,8 @@ bitflags::bitflags! {
         /// Support for `quantizeToF16`, `pack2x16float`, and `unpack2x16float`, which store
         /// `f16`-precision values in `f32`s.
         const SHADER_FLOAT16_IN_FLOAT32 = 1 << 28;
+        /// Support for fragment shader barycentric coordinates.
+        const SHADER_BARYCENTRICS = 1 << 29;
     }
 }
 
diff --git a/tests/tests/wgpu-gpu/main.rs b/tests/tests/wgpu-gpu/main.rs
@@ -54,6 +54,7 @@ mod resource_error;
 mod samplers;
 mod scissor_tests;
 mod shader;
+mod shader_barycentric;
 mod shader_primitive_index;
 mod shader_view_format;
 mod subgroup_operations;
@@ -125,6 +126,7 @@ fn all_tests() -> Vec<wgpu_test::GpuTestInitializer> {
     samplers::all_tests(&mut tests);
     scissor_tests::all_tests(&mut tests);
     shader_primitive_index::all_tests(&mut tests);
+    shader_barycentric::all_tests(&mut tests);
     shader_view_format::all_tests(&mut tests);
     shader::all_tests(&mut tests);
     subgroup_operations::all_tests(&mut tests);
diff --git a/tests/tests/wgpu-gpu/shader_barycentric/barycentric.wgsl b/tests/tests/wgpu-gpu/shader_barycentric/barycentric.wgsl
@@ -0,0 +1,9 @@
+@vertex
+fn vs_main(@location(0) xy: vec2<f32>) -> @builtin(position) vec4<f32> {
+    return vec4<f32>(xy, 0.0, 1.0);
+}
+
+@fragment
+fn fs_main(@builtin(barycentric) bary: vec3<f32>) -> @location(0) vec4<f32> {
+    return vec4<f32>(bary * 1.1 - 0.05, 1.0);
+}
diff --git a/tests/tests/wgpu-gpu/shader_barycentric/mod.rs b/tests/tests/wgpu-gpu/shader_barycentric/mod.rs
@@ -0,0 +1,164 @@
+use wgpu::util::DeviceExt;
+use wgpu_test::{gpu_test, GpuTestConfiguration, TestParameters, TestingContext};
+
+pub fn all_tests(vec: &mut Vec<wgpu_test::GpuTestInitializer>) {
+    vec.push(BARYCENTRIC);
+}
+
+//
+// This test renders one triangles to a 2x2 render target. The triangle
+// covers the bottom-left, bottom-right, and the top-left pixel.
+// XY layout of the render target, with the triangle:
+//
+//     (-1,1)  (0,1)  (1,1)
+//        +------+------+
+//        |      |      |
+//        |   o  |      |
+//        |   |\ |      |
+//        |   | \|      |
+// (-1,0) +---|--\------+ (1,0)
+//        |   |  |\     |
+//        |   |  | \    |
+//        |   o--+--o   |
+//        |      |      |
+//        +------+------+
+//     (-1,-1) (0,-1) (1,-1)
+//
+// The fragment shader outputs color based on builtin(barycentric):
+//
+//     return vec4<f32>(bary * 1.1 - 0.05, 1.0);
+//
+
+#[gpu_test]
+static BARYCENTRIC: GpuTestConfiguration = GpuTestConfiguration::new()
+    .parameters(
+        TestParameters::default()
+            .test_features_limits()
+            .features(wgpu::Features::SHADER_BARYCENTRICS),
+    )
+    .run_async(barycentric);
+
+async fn barycentric(ctx: TestingContext) {
+    let shader = ctx
+        .device
+        .create_shader_module(wgpu::include_wgsl!("barycentric.wgsl"));
+
+    let n = -0.505;
+    let p = 0.51;
+    let two_triangles_xy: [f32; 6] = [n, n, p, n, n, p];
+    let vertex_buffer = ctx
+        .device
+        .create_buffer_init(&wgpu::util::BufferInitDescriptor {
+            label: None,
+            contents: bytemuck::cast_slice(&two_triangles_xy),
+            usage: wgpu::BufferUsages::VERTEX | wgpu::BufferUsages::COPY_DST,
+        });
+
+    let indices = [0u32, 1, 2];
+    let index_buffer = ctx
+        .device
+        .create_buffer_init(&wgpu::util::BufferInitDescriptor {
+            label: None,
+            contents: bytemuck::cast_slice(&indices),
+            usage: wgpu::BufferUsages::INDEX | wgpu::BufferUsages::COPY_DST,
+        });
+
+    let pipeline = ctx
+        .device
+        .create_render_pipeline(&wgpu::RenderPipelineDescriptor {
+            label: None,
+            layout: None,
+            vertex: wgpu::VertexState {
+                module: &shader,
+                entry_point: Some("vs_main"),
+                compilation_options: Default::default(),
+                buffers: &[wgpu::VertexBufferLayout {
+                    array_stride: 8,
+                    step_mode: wgpu::VertexStepMode::Vertex,
+                    attributes: &[wgpu::VertexAttribute {
+                        format: wgpu::VertexFormat::Float32x2,
+                        offset: 0,
+                        shader_location: 0,
+                    }],
+                }],
+            },
+            primitive: wgpu::PrimitiveState::default(),
+            depth_stencil: None,
+            multisample: wgpu::MultisampleState::default(),
+            fragment: Some(wgpu::FragmentState {
+                module: &shader,
+                entry_point: Some("fs_main"),
+                compilation_options: Default::default(),
+                targets: &[Some(wgpu::ColorTargetState {
+                    format: wgpu::TextureFormat::Rgba8Unorm,
+                    blend: None,
+                    write_mask: wgpu::ColorWrites::ALL,
+                })],
+            }),
+            multiview: None,
+            cache: None,
+        });
+
+    let width = 2;
+    let height = 2;
+    let texture_size = wgpu::Extent3d {
+        width,
+        height,
+        depth_or_array_layers: 1,
+    };
+    let color_texture = ctx.device.create_texture(&wgpu::TextureDescriptor {
+        label: None,
+        size: texture_size,
+        mip_level_count: 1,
+        sample_count: 1,
+        dimension: wgpu::TextureDimension::D2,
+        format: wgpu::TextureFormat::Rgba8Unorm,
+        usage: wgpu::TextureUsages::RENDER_ATTACHMENT | wgpu::TextureUsages::COPY_SRC,
+        view_formats: &[],
+    });
+    let color_view = color_texture.create_view(&wgpu::TextureViewDescriptor::default());
+
+    let readback_buffer = wgpu_test::image::ReadbackBuffers::new(&ctx.device, &color_texture);
+
+    let mut encoder = ctx
+        .device
+        .create_command_encoder(&wgpu::CommandEncoderDescriptor::default());
+    {
+        let mut rpass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
+            label: None,
+            color_attachments: &[Some(wgpu::RenderPassColorAttachment {
+                ops: wgpu::Operations {
+                    load: wgpu::LoadOp::Clear(wgpu::Color::WHITE),
+                    store: wgpu::StoreOp::Store,
+                },
+                resolve_target: None,
+                view: &color_view,
+                depth_slice: None,
+            })],
+            depth_stencil_attachment: None,
+            timestamp_writes: None,
+            occlusion_query_set: None,
+        });
+
+        rpass.set_pipeline(&pipeline);
+        rpass.set_index_buffer(index_buffer.slice(..), wgpu::IndexFormat::Uint32);
+        rpass.set_vertex_buffer(0, vertex_buffer.slice(..));
+        rpass.draw(0..3, 0..1);
+    }
+    readback_buffer.copy_from(&ctx.device, &mut encoder, &color_texture);
+    ctx.queue.submit(Some(encoder.finish()));
+
+    //
+    //   +-----+-----+
+    //   |blue |white|
+    //   +-----+-----+
+    //   | red |green|
+    //   +-----+-----+
+    //
+    let expected = [
+        0, 0, 255, 255, 255, 255, 255, 255, 255, 0, 0, 255, 0, 255, 0, 255,
+    ];
+    readback_buffer
+        .assert_buffer_contents(&ctx, &expected)
+        .await;
+}
diff --git a/wgpu-core/src/device/mod.rs b/wgpu-core/src/device/mod.rs
@@ -510,6 +510,10 @@ pub fn create_validator(
         Caps::TEXTURE_EXTERNAL,
         features.intersects(wgt::Features::EXTERNAL_TEXTURE),
     );
+    caps.set(
+        Caps::SHADER_BARYCENTRICS,
+        features.intersects(wgt::Features::SHADER_BARYCENTRICS),
+    );
 
     naga::valid::Validator::new(flags, caps)
 }
diff --git a/wgpu-hal/src/dx12/adapter.rs b/wgpu-hal/src/dx12/adapter.rs
@@ -544,6 +544,22 @@ impl super::Adapter {
             wgt::Features::EXPERIMENTAL_MESH_SHADER,
             mesh_shader_supported,
         );
+        let shader_barycentrics_supported = {
+            let mut features3 = Direct3D12::D3D12_FEATURE_DATA_D3D12_OPTIONS3::default();
+            unsafe {
+                device.CheckFeatureSupport(
+                    Direct3D12::D3D12_FEATURE_D3D12_OPTIONS3,
+                    <*mut _>::cast(&mut features3),
+                    size_of_val(&features3) as u32,
+                )
+            }
+            .is_ok()
+                && features3.BarycentricsSupported.as_bool()
+        };
+        features.set(
+            wgt::Features::SHADER_BARYCENTRICS,
+            shader_barycentrics_supported,
+        );
 
         // TODO: Determine if IPresentationManager is supported
         let presentation_timer = auxil::dxgi::time::PresentationTimer::new_dxgi();
diff --git a/wgpu-hal/src/metal/adapter.rs b/wgpu-hal/src/metal/adapter.rs
@@ -902,6 +902,7 @@ impl super::PrivateCapabilities {
                 && (device.supports_family(MTLGPUFamily::Apple7)
                     || device.supports_family(MTLGPUFamily::Mac2)),
             supports_shared_event: version.at_least((10, 14), (12, 0), os_is_mac),
+            shader_barycentrics: device.supports_shader_barycentric_coordinates(),
         }
     }
 
@@ -997,6 +998,11 @@ impl super::PrivateCapabilities {
 
         features.set(F::RG11B10UFLOAT_RENDERABLE, self.format_rg11b10_all);
 
+        features.set(
+            F::SHADER_BARYCENTRICS,
+            self.shader_barycentrics && self.msl_version >= MTLLanguageVersion::V2_2,
+        );
+
         if self.supports_simd_scoped_operations {
             features.insert(F::SUBGROUP | F::SUBGROUP_BARRIER);
         }
diff --git a/wgpu-hal/src/metal/mod.rs b/wgpu-hal/src/metal/mod.rs
@@ -300,6 +300,7 @@ struct PrivateCapabilities {
     int64_atomics: bool,
     float_atomics: bool,
     supports_shared_event: bool,
+    shader_barycentrics: bool,
 }
 
 #[derive(Clone, Debug)]
diff --git a/wgpu-hal/src/vulkan/adapter.rs b/wgpu-hal/src/vulkan/adapter.rs
diff --git a/wgpu-types/src/features.rs b/wgpu-types/src/features.rs
