(Naga) Implement OpImageGather and OpImageDrefGather when ingesting SPIR-V (#8280)

Author: hasenbanck

CHANGELOG.md

@@ -201,7 +201,8 @@ By @cwfitzgerald in [#8162](https://github.com/gfx-rs/wgpu/pull/8162).
 - The [`source()`](https://doc.rust-lang.org/std/error/trait.Error.html#method.source) method of `ShaderError` no longer reports the error as its own source. By @andyleiserson in [#8258](https://github.com/gfx-rs/wgpu/pull/8258).
 - naga correctly ingests SPIR-V that use descriptor runtime indexing, which in turn is correctly converted into WGSLs binding array. By @hasenbanck in [8256](https://github.com/gfx-rs/wgpu/pull/8256).
 - naga correctly ingests SPIR-V that loads from multi-sampled textures, which in turn is correctly converted into WGSLs texture_multisampled_2d and load operations. By @hasenbanck in [8270](https://github.com/gfx-rs/wgpu/pull/8270).
- 
+- naga implement OpImageGather and OpImageDrefGather operations when ingesting SPIR-V. By @hasenbanck in [8280](https://github.com/gfx-rs/wgpu/pull/8280).
+
 #### DX12
 
 - Allow disabling waiting for latency waitable object. By @marcpabst in [#7400](https://github.com/gfx-rs/wgpu/pull/7400)

naga/src/front/spv/image.rs

@@ -48,6 +48,8 @@ pub struct SamplingOptions {
     pub project: bool,
     /// Depth comparison sampling with a reference value.
     pub compare: bool,
+    /// Gather sampling: Operates on four samples of one channel.
+    pub gather: bool,
 }
 
 enum ExtraCoordinate {
@@ -500,10 +502,10 @@ impl<I: Iterator<Item = u32>> super::Frontend<I> {
         let result_id = self.next()?;
         let sampled_image_id = self.next()?;
         let coordinate_id = self.next()?;
-        let dref_id = if options.compare {
-            Some(self.next()?)
-        } else {
-            None
+        let (component_id, dref_id) = match (options.gather, options.compare) {
+            (true, false) => (Some(self.next()?), None),
+            (_, true) => (None, Some(self.next()?)),
+            (_, _) => (None, None),
         };
         let span = self.span_from_with_op(start);
 
@@ -629,6 +631,58 @@ impl<I: Iterator<Item = u32>> super::Frontend<I> {
             self.get_expr_handle(coordinate_id, coord_lexp, ctx, emitter, block, body_idx);
         let coord_type_handle = self.lookup_type.lookup(coord_lexp.type_id)?.handle;
 
+        let gather = match (options.gather, component_id) {
+            (true, Some(component_id)) => {
+                let component_lexp = self.lookup_expression.lookup(component_id)?;
+
+                let component_value = match ctx.expressions[component_lexp.handle] {
+                    // VUID-StandaloneSpirv-OpImageGather-04664:
+                    // The “Component” operand of OpImageGather, and OpImageSparseGather must be the
+                    // <id> of a constant instruction.
+                    crate::Expression::Constant(const_handle) => {
+                        let constant = &ctx.module.constants[const_handle];
+                        match ctx.module.global_expressions[constant.init] {
+                            // SPIR-V specification: "It must be a 32-bit integer type scalar."
+                            crate::Expression::Literal(crate::Literal::U32(value)) => value,
+                            crate::Expression::Literal(crate::Literal::I32(value)) => value as u32,
+                            _ => {
+                                log::error!(
+                                    "Image gather component constant must be a 32-bit integer literal"
+                                );
+                                return Err(Error::InvalidOperand);
+                            }
+                        }
+                    }
+                    _ => {
+                        log::error!("Image gather component must be a constant");
+                        return Err(Error::InvalidOperand);
+                    }
+                };
+
+                debug_assert_eq!(level, crate::SampleLevel::Auto);
+                level = crate::SampleLevel::Zero;
+
+                // SPIR-V specification: "Behavior is undefined if its value is not 0, 1, 2 or 3."
+                match component_value {
+                    0 => Some(crate::SwizzleComponent::X),
+                    1 => Some(crate::SwizzleComponent::Y),
+                    2 => Some(crate::SwizzleComponent::Z),
+                    3 => Some(crate::SwizzleComponent::W),
+                    other => {
+                        log::error!("Invalid gather component operand: {other}");
+                        return Err(Error::InvalidOperand);
+                    }
+                }
+            }
+            (true, None) => {
+                debug_assert_eq!(level, crate::SampleLevel::Auto);
+                level = crate::SampleLevel::Zero;
+
+                Some(crate::SwizzleComponent::X)
+            }
+            (_, _) => None,
+        };
+
         let sampling_bit = if options.compare {
             SamplingFlags::COMPARISON
         } else {
@@ -745,7 +799,7 @@ impl<I: Iterator<Item = u32>> super::Frontend<I> {
         let expr = crate::Expression::ImageSample {
             image: si_lexp.image,
             sampler: si_lexp.sampler,
-            gather: None, //TODO
+            gather,
             coordinate,
             array_index,
             offset,

naga/src/front/spv/mod.rs

@@ -2802,6 +2802,7 @@ impl<I: Iterator<Item = u32>> Frontend<I> {
                     let options = image::SamplingOptions {
                         compare: false,
                         project: false,
+                        gather: false,
                     };
                     self.parse_image_sample(
                         extra,
@@ -2818,6 +2819,7 @@ impl<I: Iterator<Item = u32>> Frontend<I> {
                     let options = image::SamplingOptions {
                         compare: false,
                         project: true,
+                        gather: false,
                     };
                     self.parse_image_sample(
                         extra,
@@ -2834,6 +2836,7 @@ impl<I: Iterator<Item = u32>> Frontend<I> {
                     let options = image::SamplingOptions {
                         compare: true,
                         project: false,
+                        gather: false,
                     };
                     self.parse_image_sample(
                         extra,
@@ -2850,6 +2853,41 @@ impl<I: Iterator<Item = u32>> Frontend<I> {
                     let options = image::SamplingOptions {
                         compare: true,
                         project: true,
+                        gather: false,
+                    };
+                    self.parse_image_sample(
+                        extra,
+                        options,
+                        ctx,
+                        &mut emitter,
+                        &mut block,
+                        block_id,
+                        body_idx,
+                    )?;
+                }
+                Op::ImageGather => {
+                    let extra = inst.expect_at_least(6)?;
+                    let options = image::SamplingOptions {
+                        compare: false,
+                        project: false,
+                        gather: true,
+                    };
+                    self.parse_image_sample(
+                        extra,
+                        options,
+                        ctx,
+                        &mut emitter,
+                        &mut block,
+                        block_id,
+                        body_idx,
+                    )?;
+                }
+                Op::ImageDrefGather => {
+                    let extra = inst.expect_at_least(6)?;
+                    let options = image::SamplingOptions {
+                        compare: true,
+                        project: false,
+                        gather: true,
                     };
                     self.parse_image_sample(
                         extra,

naga/tests/in/spv/gather-cmp.slang

@@ -0,0 +1,18 @@
+// Compiled with:
+// slangc -target spirv -profile spirv_1_5 -o naga/tests/in/spv/gather-cmp.spv naga/tests/in/spv/gather-cmp.slang
+// Disassembled with:
+// spirv-dis naga/tests/in/spv/gather-cmp.spv -o naga/tests/in/spv/gather-cmp.spvasm
+
+#language slang 2026
+
+[[vk::binding(0, 0)]] var texture: Texture2D;
+[[vk::binding(1, 0)]] var depth_sampler: SamplerComparisonState;
+
+struct VertexOutput {
+    var texture_coordinates: float2;
+};
+
+[[shader("pixel")]]
+func main(input: VertexOutput) -> float4 {
+    return texture.GatherCmp(depth_sampler, input.texture_coordinates, 0.5);
+}

naga/tests/in/spv/gather-cmp.spvasm

@@ -0,0 +1,49 @@
+; SPIR-V
+; Version: 1.5
+; Generator: Khronos Slang Compiler; 0
+; Bound: 27
+; Schema: 0
+               OpCapability Shader
+               OpMemoryModel Logical GLSL450
+               OpEntryPoint Fragment %main "main" %texture %depth_sampler %entryPointParam_main %input_texture_coordinates
+               OpExecutionMode %main OriginUpperLeft
+               OpSource Slang 1
+               OpName %input_texture_coordinates "input.texture_coordinates"
+               OpName %texture "texture"
+               OpName %depth_sampler "depth_sampler"
+               OpName %sampledImage "sampledImage"
+               OpName %entryPointParam_main "entryPointParam_main"
+               OpName %main "main"
+               OpDecorate %input_texture_coordinates Location 0
+               OpDecorate %texture Binding 0
+               OpDecorate %texture DescriptorSet 0
+               OpDecorate %depth_sampler Binding 1
+               OpDecorate %depth_sampler DescriptorSet 0
+               OpDecorate %entryPointParam_main Location 0
+       %void = OpTypeVoid
+          %3 = OpTypeFunction %void
+      %float = OpTypeFloat 32
+    %v2float = OpTypeVector %float 2
+%_ptr_Input_v2float = OpTypePointer Input %v2float
+         %10 = OpTypeImage %float 2D 2 0 0 1 Unknown
+%_ptr_UniformConstant_10 = OpTypePointer UniformConstant %10
+         %14 = OpTypeSampler
+%_ptr_UniformConstant_14 = OpTypePointer UniformConstant %14
+         %18 = OpTypeSampledImage %10
+    %v4float = OpTypeVector %float 4
+  %float_0_5 = OpConstant %float 0.5
+%_ptr_Output_v4float = OpTypePointer Output %v4float
+%input_texture_coordinates = OpVariable %_ptr_Input_v2float Input
+    %texture = OpVariable %_ptr_UniformConstant_10 UniformConstant
+%depth_sampler = OpVariable %_ptr_UniformConstant_14 UniformConstant
+%entryPointParam_main = OpVariable %_ptr_Output_v4float Output
+       %main = OpFunction %void None %3
+          %4 = OpLabel
+          %7 = OpLoad %v2float %input_texture_coordinates
+         %11 = OpLoad %10 %texture
+         %15 = OpLoad %14 %depth_sampler
+%sampledImage = OpSampledImage %18 %11 %15
+         %21 = OpImageDrefGather %v4float %sampledImage %7 %float_0_5
+               OpStore %entryPointParam_main %21
+               OpReturn
+               OpFunctionEnd

naga/tests/in/spv/gather-cmp.toml

@@ -0,0 +1,4 @@
+god_mode = true
+
+[spv-in]
+adjust_coordinate_space = true

naga/tests/in/spv/gather.slang

@@ -0,0 +1,18 @@
+// Compiled with:
+// slangc -target spirv -profile spirv_1_5 -o naga/tests/in/spv/gather.spv naga/tests/in/spv/gather.slang
+// Disassembled with:
+// spirv-dis naga/tests/in/spv/gather.spv -o naga/tests/in/spv/gather.spvasm
+
+#language slang 2026
+
+[[vk::binding(0, 0)]] var texture: Texture2D;
+[[vk::binding(1, 0)]] var linear_sampler: SamplerState;
+
+struct VertexOutput {
+    var texture_coordinates: float2;
+};
+
+[[shader("pixel")]]
+func main(input: VertexOutput) -> float4 {
+    return texture.GatherGreen(linear_sampler, input.texture_coordinates);
+}

naga/tests/in/spv/gather.spvasm

@@ -0,0 +1,50 @@
+; SPIR-V
+; Version: 1.5
+; Generator: Khronos Slang Compiler; 0
+; Bound: 28
+; Schema: 0
+               OpCapability Shader
+               OpMemoryModel Logical GLSL450
+               OpEntryPoint Fragment %main "main" %texture %linear_sampler %entryPointParam_main %input_texture_coordinates
+               OpExecutionMode %main OriginUpperLeft
+               OpSource Slang 1
+               OpName %input_texture_coordinates "input.texture_coordinates"
+               OpName %texture "texture"
+               OpName %linear_sampler "linear_sampler"
+               OpName %sampledImage "sampledImage"
+               OpName %entryPointParam_main "entryPointParam_main"
+               OpName %main "main"
+               OpDecorate %input_texture_coordinates Location 0
+               OpDecorate %texture Binding 0
+               OpDecorate %texture DescriptorSet 0
+               OpDecorate %linear_sampler Binding 1
+               OpDecorate %linear_sampler DescriptorSet 0
+               OpDecorate %entryPointParam_main Location 0
+       %void = OpTypeVoid
+          %3 = OpTypeFunction %void
+      %float = OpTypeFloat 32
+    %v2float = OpTypeVector %float 2
+%_ptr_Input_v2float = OpTypePointer Input %v2float
+         %10 = OpTypeImage %float 2D 2 0 0 1 Unknown
+%_ptr_UniformConstant_10 = OpTypePointer UniformConstant %10
+         %14 = OpTypeSampler
+%_ptr_UniformConstant_14 = OpTypePointer UniformConstant %14
+         %18 = OpTypeSampledImage %10
+    %v4float = OpTypeVector %float 4
+        %int = OpTypeInt 32 1
+      %int_1 = OpConstant %int 1
+%_ptr_Output_v4float = OpTypePointer Output %v4float
+%input_texture_coordinates = OpVariable %_ptr_Input_v2float Input
+    %texture = OpVariable %_ptr_UniformConstant_10 UniformConstant
+%linear_sampler = OpVariable %_ptr_UniformConstant_14 UniformConstant
+%entryPointParam_main = OpVariable %_ptr_Output_v4float Output
+       %main = OpFunction %void None %3
+          %4 = OpLabel
+          %7 = OpLoad %v2float %input_texture_coordinates
+         %11 = OpLoad %10 %texture
+         %15 = OpLoad %14 %linear_sampler
+%sampledImage = OpSampledImage %18 %11 %15
+         %21 = OpImageGather %v4float %sampledImage %7 %int_1
+               OpStore %entryPointParam_main %21
+               OpReturn
+               OpFunctionEnd

naga/tests/in/spv/gather.toml

@@ -0,0 +1,4 @@
+god_mode = true
+
+[spv-in]
+adjust_coordinate_space = true

naga/tests/out/wgsl/spv-gather-cmp.wgsl

@@ -0,0 +1,21 @@
+var<private> inputtexture_coordinates_1: vec2<f32>;
+@group(0) @binding(0) 
+var texture: texture_depth_2d;
+@group(0) @binding(1) 
+var depth_sampler: sampler_comparison;
+var<private> entryPointParam_main: vec4<f32>;
+
+fn main_1() {
+    let _e5 = inputtexture_coordinates_1;
+    let _e6 = textureGatherCompare(texture, depth_sampler, _e5, 0.5f);
+    entryPointParam_main = _e6;
+    return;
+}
+
+@fragment 
+fn main(@location(0) inputtexture_coordinates: vec2<f32>) -> @location(0) vec4<f32> {
+    inputtexture_coordinates_1 = inputtexture_coordinates;
+    main_1();
+    let _e3 = entryPointParam_main;
+    return _e3;
+}