2 files changed, 53 insertions, 23 deletions

diff --git a/source/slang/slang-emit-spirv.cpp b/source/slang/slang-emit-spirv.cpp
index a5a77e148..0a755cd6d 100644
--- a/source/slang/slang-emit-spirv.cpp
+++ b/source/slang/slang-emit-spirv.cpp
@@ -6211,11 +6211,24 @@ struct SPIRVEmitContext : public SourceEmitterBase, public SPIRVEmitSharedContex
                     requireSPIRVCapability(SpvCapabilityFragmentBarycentricKHR);
                     ensureExtensionDeclaration(
                         UnownedStringSlice("SPV_KHR_fragment_shader_barycentric"));
-                    return getBuiltinGlobalVar(inst->getFullType(), SpvBuiltInBaryCoordKHR, inst);
 
-                    // TODO: There is also the `gl_BaryCoordNoPerspNV` builtin, which
-                    // we ought to use if the `noperspective` modifier has been
-                    // applied to this varying input.
+                    auto interpolationModeDecor =
+                        inst->findDecoration<IRInterpolationModeDecoration>();
+                    if (interpolationModeDecor &&
+                        interpolationModeDecor->getMode() == IRInterpolationMode::NoPerspective)
+                    {
+                        return getBuiltinGlobalVar(
+                            inst->getFullType(),
+                            SpvBuiltInBaryCoordNoPerspKHR,
+                            inst);
+                    }
+                    else
+                    {
+                        return getBuiltinGlobalVar(
+                            inst->getFullType(),
+                            SpvBuiltInBaryCoordKHR,
+                            inst);
+                    }
                 }
                 else if (semanticName == "sv_cullprimitive")
                 {
diff --git a/source/slang/slang-ir-glsl-legalize.cpp b/source/slang/slang-ir-glsl-legalize.cpp
index dce85efd3..d1a534c66 100644
--- a/source/slang/slang-ir-glsl-legalize.cpp
+++ b/source/slang/slang-ir-glsl-legalize.cpp
@@ -391,6 +391,20 @@ GLSLSystemValueInfo* getMeshOutputIndicesSystemValueInfo(
     SLANG_UNREACHABLE("Unhandled mesh output indices type");
 }
 
+// Hold the in-stack linked list that represents the access chain
+// to the current global varying parameter being created.
+// e.g. if the user code has:
+//    struct Params { in float member; }
+//    void main(in Params inParams);
+// Then the `outerParamInfo` when we get to `createSimpleGLSLVarying` for `member`
+// will be:  {IRStructField member} -> {IRParam inParams} -> {IRFunc main}.
+//
+struct OuterParamInfoLink
+{
+    IRInst* outerParam;
+    OuterParamInfoLink* next;
+};
+
 GLSLSystemValueInfo* getGLSLSystemValueInfo(
     GLSLLegalizationContext* context,
     CodeGenContext* codeGenContext,
@@ -399,7 +413,8 @@ GLSLSystemValueInfo* getGLSLSystemValueInfo(
     Stage stage,
     IRType* type,
     GlobalVaryingDeclarator* declarator,
-    GLSLSystemValueInfo* inStorage)
+    GLSLSystemValueInfo* inStorage,
+    OuterParamInfoLink* outerParamInfo)
 {
     SLANG_UNUSED(codeGenContext);
 
@@ -864,11 +879,26 @@ GLSLSystemValueInfo* getGLSLSystemValueInfo(
         context->requireGLSLVersion(ProfileVersion::GLSL_450);
         context->requireGLSLExtension(
             UnownedStringSlice::fromLiteral("GL_EXT_fragment_shader_barycentric"));
+
         name = "gl_BaryCoordEXT";
 
-        // TODO: There is also the `gl_BaryCoordNoPerspNV` builtin, which
-        // we ought to use if the `noperspective` modifier has been
-        // applied to this varying input.
+        // Search for nointerpolation keyword to use no-perspective variant of BaryCoord
+        for (auto paramInfo = outerParamInfo; paramInfo; paramInfo = paramInfo->next)
+        {
+            auto outerParam = paramInfo->outerParam;
+            auto decorParent = outerParam;
+            if (auto field = as<IRStructField>(decorParent))
+                decorParent = field->getKey();
+            auto interpolation = decorParent->findDecoration<IRInterpolationModeDecoration>();
+            if (!interpolation || interpolation->getMode() != IRInterpolationMode::NoPerspective)
+                continue;
+            name = "gl_BaryCoordNoPerspEXT";
+            break;
+        }
+
+        requiredType = builder->getVectorType(
+            builder->getBasicType(BaseType::Float),
+            builder->getIntValue(builder->getIntType(), 3));
     }
     else if (semanticName == "sv_cullprimitive")
     {
@@ -938,20 +968,6 @@ GLSLSystemValueInfo* getGLSLSystemValueInfo(
     return nullptr;
 }
 
-// Hold the in-stack linked list that represents the access chain
-// to the current global varying parameter being created.
-// e.g. if the user code has:
-//    struct Params { in float member; }
-//    void main(in Params inParams);
-// Then the `outerParamInfo` when we get to `createSimpleGLSLVarying` for `member`
-// will be:  {IRStructField member} -> {IRParam inParams} -> {IRFunc main}.
-//
-struct OuterParamInfoLink
-{
-    IRInst* outerParam;
-    OuterParamInfoLink* next;
-};
-
 void createVarLayoutForLegalizedGlobalParam(
     GLSLLegalizationContext* context,
     IRInst* globalParam,
@@ -1318,7 +1334,8 @@ ScalarizedVal createSimpleGLSLGlobalVarying(
         stage,
         inType,
         declarator,
-        &systemValueInfoStorage);
+        &systemValueInfoStorage,
+        outerParamInfo);
 
     {