Fix mesh shader per primitive spirv annotation

source/slang/core.meta.slang

@@ -41,6 +41,9 @@ syntax globallycoherent : GloballyCoherentModifier;
 ///
 syntax pervertex : PerVertexModifier;
 
+/// Modifier to disable inteprolation and force per-primitive passing of a varying attribute.
+syntax perprimitive : PerPrimitiveModifier;
+
 /// Modifier to indicate a buffer or texture element type is
 /// backed by data in an unsigned normalized format.
 ///

source/slang/slang-ast-modifier.h

@@ -711,6 +711,13 @@ class PerVertexModifier : public InterpolationModeModifier
     FIDDLE(...)
 };
 
+/// Slang-defined `perprimitive` modifier
+FIDDLE()
+class PerPrimitiveModifier : public Modifier
+{
+    FIDDLE(...)
+};
+
 
 // HLSL `precise` modifier
 FIDDLE()

source/slang/slang-check-modifier.cpp

@@ -1374,6 +1374,7 @@ ASTNodeType getModifierConflictGroupKind(ASTNodeType modifierType)
     case ASTNodeType::HLSLSampleModifier:
     case ASTNodeType::HLSLCentroidModifier:
     case ASTNodeType::PerVertexModifier:
+    case ASTNodeType::PerPrimitiveModifier:
         return ASTNodeType::InterpolationModeModifier;
 
     case ASTNodeType::PrefixModifier:
@@ -1466,6 +1467,7 @@ bool isModifierAllowedOnDecl(bool isGLSLInput, ASTNodeType modifierType, Decl* d
     case ASTNodeType::HLSLSampleModifier:
     case ASTNodeType::HLSLCentroidModifier:
     case ASTNodeType::PerVertexModifier:
+    case ASTNodeType::PerPrimitiveModifier:
     case ASTNodeType::HLSLUniformModifier:
     case ASTNodeType::DynamicUniformModifier:
         return (as<VarDeclBase>(decl) &&

source/slang/slang-emit-glsl.cpp

@@ -160,6 +160,12 @@ void GLSLSourceEmitter::_requireFragmentShaderBarycentric()
     m_glslExtensionTracker->requireVersion(ProfileVersion::GLSL_450);
 }
 
+void GLSLSourceEmitter::_requireMeshShader()
+{
+    m_glslExtensionTracker->requireExtension(
+        UnownedStringSlice::fromLiteral("GL_EXT_mesh_shader"));
+    m_glslExtensionTracker->requireVersion(ProfileVersion::GLSL_450);
+}
 
 void GLSLSourceEmitter::_requireGLSLExtension(const UnownedStringSlice& name)
 {
@@ -3723,6 +3729,7 @@ void GLSLSourceEmitter::emitMeshShaderModifiersImpl(IRInst* varInst)
 {
     if (varInst->findDecoration<IRGLSLPrimitivesRateDecoration>())
     {
+        _requireMeshShader();
         m_writer->emit("perprimitiveEXT");
         m_writer->emit(" ");
     }

source/slang/slang-emit-glsl.h

@@ -176,6 +176,8 @@ class GLSLSourceEmitter : public CLikeSourceEmitter
 
     void _requireFragmentShaderBarycentric();
 
+    void _requireMeshShader();
+
     void _emitSpecialFloatImpl(IRType* type, const char* valueExpr);
 
     void emitAtomicImageCoord(IRImageSubscript* operand);

source/slang/slang-emit-spirv.cpp

@@ -2945,6 +2945,7 @@ struct SPIRVEmitContext : public SourceEmitterBase, public SPIRVEmitSharedContex
             return false;
         }
     }
+
     void emitSystemVarDecoration(IRInst* var, SpvInst* varInst)
     {
         for (auto decor : var->getDecorations())
@@ -3084,7 +3085,7 @@ struct SPIRVEmitContext : public SourceEmitterBase, public SPIRVEmitSharedContex
                 SpvLiteralInteger::from32(int32_t(0)));
         }
 
-        bool anyModifiers = (var->findDecoration<IRInterpolationModeDecoration>() != nullptr);
+        bool anyModifiers = (var->findDecoration<IRInterpolationModeDecoration>() != nullptr || var->findDecoration<IRGLSLPrimitivesRateDecoration>() != nullptr);
 
         // If the user didn't explicitly qualify a varying
         // with integer or pointer type, then we need to explicitly
@@ -3111,13 +3112,6 @@ struct SPIRVEmitContext : public SourceEmitterBase, public SPIRVEmitSharedContex
         {
             switch (decor->getOp())
             {
-            case kIROp_GLSLPrimitivesRateDecoration:
-                emitOpDecorate(
-                    getSection(SpvLogicalSectionID::Annotations),
-                    decor,
-                    varInst,
-                    SpvDecorationPerPrimitiveEXT);
-                break;
             case kIROp_RequireSPIRVDescriptorIndexingExtensionDecoration:
                 ensureExtensionDeclarationBeforeSpv15(
                     UnownedStringSlice("SPV_EXT_descriptor_indexing"));
@@ -5609,6 +5603,15 @@ struct SPIRVEmitContext : public SourceEmitterBase, public SPIRVEmitSharedContex
                 dstID,
                 SpvDecorationPerVertexKHR);
             break;
+        case kIROp_GLSLPrimitivesRateDecoration:
+            ensureExtensionDeclaration(UnownedStringSlice("SPV_EXT_mesh_shader"));
+            requireSPIRVAnyCapability({SpvCapabilityMeshShadingEXT});
+            emitOpDecorate(
+                getSection(SpvLogicalSectionID::Annotations),
+                decoration,
+                dstID,
+                SpvDecorationPerPrimitiveEXT);
+                break;
         case kIROp_OutputControlPointsDecoration:
             requireSPIRVExecutionMode(
                 decoration,

source/slang/slang-ir-glsl-legalize.cpp

@@ -1007,6 +1007,12 @@ void createVarLayoutForLegalizedGlobalParam(
             builder->addInterpolationModeDecoration(globalParam, interpolationModeDecor->getMode());
             break;
         }
+
+        if (decorParent->findDecoration<IRGLSLPrimitivesRateDecoration>())
+        {
+            builder->addSimpleDecoration<IRGLSLPrimitivesRateDecoration>(globalParam);
+            break;
+        }
     }
 
     if (declarator && declarator->flavor == GlobalVaryingDeclarator::Flavor::meshOutputPrimitives)

source/slang/slang-lower-to-ir.cpp

@@ -2626,6 +2626,10 @@ void addVarDecorations(IRGenContext* context, IRInst* inst, Decl* decl)
             if (op != kIROp_Invalid)
                 builder->addDecoration(inst, op);
         }
+        else if (as<PerPrimitiveModifier>(mod))
+        {
+            builder->addSimpleDecoration<IRGLSLPrimitivesRateDecoration>(inst);
+        }
         // TODO: what are other modifiers we need to propagate through?
     }
     if (auto t = composeGetters<IRMeshOutputType>(

tests/spirv/mesh-primitive.slang

@@ -1,40 +1,62 @@
-//TEST:SIMPLE(filecheck=CHECK): -target spirv -emit-spirv-directly
+// TEST:SIMPLE(filecheck=CHECK): -target spirv -emit-spirv-directly
 
-// CHECK: OpDecorate %primitives_color Location 0
-// CHECK: OpDecorate %primitives_color PerPrimitive
-// CHECK: OpDecorate %prim_color Location 0
-// CHECK: OpDecorate %prim_color Flat
+// VUID-CullPrimitiveEXT-CullPrimitiveEXT-07038
+// CHECK: OpDecorate %[[CULLPRIMITIVE:[0-9]+]] BuiltIn CullPrimitiveEXT
+// CHECK: OpDecorate %[[CULLPRIMITIVE]] PerPrimitive
+
+// CHECK: OpDecorate %gl_PrimitiveID BuiltIn PrimitiveId
+// CHECK: OpDecorate %gl_PrimitiveID PerPrimitiveEXT
+// CHECK: OpDecorate %out_primitives_color Location 0
+// CHECK: OpDecorate %out_primitives_color PerPrimitiveEXT
+// CHECK: OpDecorate %out_primitives_values Location 2
+// CHECK: OpDecorate %out_primitives_values PerPrimitiveEXT
+// CHECK: OpDecorate %entryPointParam_entry_mesh_out_normal Location 1
+// CHECK: OpDecorate %entryPointParam_entry_mesh_out_normal PerPrimitiveEXT
+
+// CHECK: OpDecorate %gl_PrimitiveID_0 BuiltIn PrimitiveId
+// CHECK: OpDecorate %gl_PrimitiveID_0 PerPrimitiveEXT
+// CHECK: OpDecorate %in_normal Location 1
+// CHECK: OpDecorate %in_normal PerPrimitiveEXT
+// CHECK: OpDecorate %in_color Location 0
+// CHECK: OpDecorate %in_color PerPrimitiveEXT
+// CHECK: OpDecorate %in_values Location 2
+// CHECK: OpDecorate %in_values PerPrimitiveEXT
 
 const static uint MAX_VERTS = 6;
 const static uint MAX_PRIMS = 2;
 
 const static float2 positions[MAX_VERTS] = {
-  float2(0.0, -0.5),
-  float2(0.5, 0),
-  float2(-0.5, 0),
-  float2(0.0, 0.5),
-  float2(0.5, 0),
-  float2(-0.5, 0),
+    float2(0.0, -0.5),
+    float2(0.5, 0),
+    float2(-0.5, 0),
+    float2(0.0, 0.5),
+    float2(0.5, 0),
+    float2(-0.5, 0),
 };
 
 struct Vertex
 {
-  float4 pos : SV_Position;
+    float4 pos : SV_Position;
 };
 
 struct Primitive
 {
-  [[vk::location(0)]] float3 color;
+    bool cull : SV_CullPrimitive;
+    uint primitive_id : SV_PrimitiveID;
+    [[vk::location(0)]] float3 color;
+    [[vk::location(2)]] float values[2];
 }
 
+[[vk::location(1)]] out perprimitive float3 out_normal[MAX_PRIMS];
+
 [outputtopology("triangle")]
 [numthreads(MAX_VERTS, 1, 1)]
 [shader("mesh")]
 void entry_mesh(
     in uint tig : SV_GroupThreadID,
     OutputVertices<Vertex, MAX_VERTS> verts,
     OutputIndices<uint3, MAX_PRIMS> triangles,
-    OutputPrimitives<Primitive, MAX_PRIMS> primitives)
+    OutputPrimitives<Primitive, MAX_PRIMS> out_primitives)
 {
     const uint numVertices = MAX_VERTS;
     const uint numPrimitives = MAX_PRIMS;
@@ -44,21 +66,28 @@ void entry_mesh(
         verts[tig] = {float4(positions[tig], 0, 1)};
     }
 
-    if(tig < numPrimitives) {
-        triangles[tig] = uint3(0,1,2) + tig * 3;
-        primitives[tig] = { float3(1,0,0) };
+    if (tig < numPrimitives) {
+        triangles[tig] = uint3(0, 1, 2) + tig * 3;
+        out_primitives[tig] = { false, tig, float3(1, 0, 0) };
+        out_normal[tig] = float3(1.0, 0.0, 0.0);
     }
 }
 
 struct FragmentOut
 {
-    [[vk::location(0)]] float3 color;
+    [[vk::location(0)]] float3 frag_color;
 };
 
+[[vk::location(1)]] in perprimitive float3 in_normal;
+[[vk::location(2)]] in perprimitive float in_values[2];
+in perprimitive uint in_primitive_id : SV_PrimitiveID;
+
 [shader("fragment")]
-FragmentOut entry_fragment(in nointerpolation Primitive prim)
+FragmentOut entry_fragment([[vk::location(0)]] in perprimitive float3 in_color, )
 {
+    let n_dot_l = dot(in_normal, float3(0.0, 1.0, 0.0)) + in_values[0] + in_primitive_id;
+
     FragmentOut frag_out;
-    frag_out.color = prim.color;
+    frag_out.frag_color = in_color * n_dot_l;
     return frag_out;
 }