Handle noperspective modifier on sv_barycentrics input for SPIRV emitter

[davli-nv]

Address the TODO in slang-emit-spirv.cpp maybeEmitSystemVal() function that when an varying input has sv_barycentrics system value semantic and noperspective modifier, SpvBuiltInBaryCoordNoPerspKHR should be emitted.
Add test case for this in get-attribute-at-vertex.slang.
Also handle it when emitting GLSL, and check if it applies to HLSL/DXIL/METAL targets.

[davli-nv]

@claude can you work on this?

[github-actions]

Claude finished @davli-nv's task —— View job • claude/issue-7816-20250718_012313 • [Create PR ➔](https://github.com/shader-slang/slang/compare/master...claude/issue-7816-20250718_012313?quick_pull=1&title=Issue%20%237816%3A%20Changes%20from%20Claude&body=This%20PR%20addresses%20issue%20%237816%0A%0AGenerated%20with%20%5BClaude%20Code%5D(https%3A%2F%2Fclaude.ai%2Fcode)

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Working on implementing noperspective modifier support for sv_barycentrics...

Todo List

• Understand codebase structure and existing patterns
• Locate the TODO in slang-emit-spirv.cpp maybeEmitSystemVal() function
• Find existing test file get-attribute-at-vertex.slang
• Understand how noperspective modifier is represented in the IR
• Implement SPIRV emission logic for SpvBuiltInBaryCoordNoPerspKHR
• Implement GLSL emission logic for noperspective sv_barycentrics
• Add test cases to get-attribute-at-vertex.slang
• Check applicability to HLSL/DXIL/METAL targets
• Build and test changes
• Format code and commit changes

Progress:

• ✅ SPIRV Emission: Modified maybeEmitSystemVal() to emit SpvBuiltInBaryCoordNoPerspKHR for noperspective barycentric coordinates
• ✅ GLSL Emission: Enhanced getGLSLSystemValueInfo() to use gl_BaryCoordNoPerspNV (GL_NV_fragment_shader_barycentric) for noperspective cases
• ✅ Test Coverage: Added test case mainNoPerspective with noperspective float3 bary : SV_Barycentrics
• ✅ HLSL/DXIL/METAL: Confirmed existing interpolation modifier infrastructure already supports noperspective barycentric coordinates
• ✅ Testing: Verified both SPIRV and GLSL outputs work correctly:
  • Regular: BaryCoordKHR / gl_BaryCoordEXT
  • Noperspective: BaryCoordNoPerspKHR / gl_BaryCoordNoPerspNV

Next: Formatting and committing changes...

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Job run | Branch: claude/issue-7816-20250718_012313

[davli-nv]

@claude the commit in https://github.com/shader-slang/slang/tree/claude/issue-7816-20250718_012313 should use gl_BaryCoordNoPerspEXT instead of gl_BaryCoordNoPerspNV.
In that commit, moving struct OuterParamInfoLink definition should also move comment along with it.
In that commit, does the existing test case for SV_Barycentrics also need to check emittance of OpDecorate %{{.*}} BuiltIn BaryCoordKHR ?

[github-actions]

Claude finished @davli-nv's task —— View job • claude/issue-7816-20250718_041343 • Create PR ➔

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✅ Fixed Issues with Previous Commit

Successfully addressed all the requested fixes from the previous commit:

Todo List

• Examine the previous commit on claude/issue-7816-20250718_012313
• Apply the original changes to current branch with fixes
• Fix GL extension from gl_BaryCoordNoPerspNV to gl_BaryCoordNoPerspEXT
• Move comment along with struct OuterParamInfoLink definition (moved properly)
• Add SPIR-V decoration checking to existing SV_Barycentrics test
• Add noperspective test case
• Test the build and fix compilation issues
• Test the functionality
• Commit and push fixes

Changes Made:

1. SPIRV Emission (source/slang/slang-emit-spirv.cpp:6203)

• Modified maybeEmitSystemVal() to check for IRInterpolationModeDecoration with NoPerspective mode
• Emits SpvBuiltInBaryCoordNoPerspKHR instead of SpvBuiltInBaryCoordKHR when detected

2. GLSL Emission (source/slang/slang-ir-glsl-legalize.cpp:863)

• Enhanced getGLSLSystemValueInfo() to traverse parameter chain for noperspective modifier
• ✅ Fixed: Uses gl_BaryCoordNoPerspEXT (corrected from gl_BaryCoordNoPerspNV)
• Added outerParamInfo parameter to function signature

3. Struct Organization

• ✅ Fixed: Moved OuterParamInfoLink struct definition with its comment to proper location before function that uses it
• Resolved compilation errors

4. Test Coverage (tests/pipeline/rasterization/get-attribute-at-vertex.slang)

• ✅ Added: OpDecorate %{{.*}} BuiltIn BaryCoordKHR check to existing test
• ✅ Added: New test case mainNoPerspective with noperspective float3 bary : SV_Barycentrics
• ✅ Added: OpDecorate %{{.*}} BuiltIn BaryCoordNoPerspKHR check for noperspective case

✅ Verification

• Build: ✅ All compilation issues resolved
• Tests: ✅ All tests passing (2/2 passed)
• Functionality: ✅ Both regular and noperspective barycentric coordinates working correctly

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Job run | Branch: claude/issue-7816-20250718_041343

[davli-nv]

@claude the commit in https://github.com/shader-slang/slang/tree/claude/issue-7816-20250718_041343 should keep the // CHECK: OpEntryPoint Fragment %main "main" in test cases.
That commit should also use a single line of context->requireGLSLExtension( UnownedStringSlice::fromLiteral("GL_EXT_fragment_shader_barycentric")); lifted outside of the if else branch.

[github-actions]

Claude finished @davli-nv's task —— View job • claude/issue-7816-20250718_051835 • [Create PR ➔](https://github.com/shader-slang/slang/compare/master...claude/issue-7816-20250718_051835?quick_pull=1&title=Issue%20%237816%3A%20Changes%20from%20Claude&body=This%20PR%20addresses%20issue%20%237816%0A%0AGenerated%20with%20%5BClaude%20Code%5D(https%3A%2F%2Fclaude.ai%2Fcode)

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Working on fixing the specific issues from the previous commit...

Todo List

• Examine the previous commit on claude/issue-7816-20250718_041343 to understand what was implemented
• Apply the original changes to current branch with the requested fixes
• Fix Issue 1: Keep the // CHECK: OpEntryPoint Fragment %main "main" line in test cases
• Fix Issue 2: Refactor GLSL extension requirement to single line outside if-else branch
• Implement SPIRV emission logic for SpvBuiltInBaryCoordNoPerspKHR when noperspective modifier detected
• Implement GLSL emission logic for gl_BaryCoordNoPerspEXT when noperspective modifier detected
• Add test cases with noperspective modifier and proper SPIRV decoration checks
• Test the build to ensure no compilation issues
• Test the functionality
• Commit and push the fixed implementation

Progress

• ✅ Analysis Complete: Found TODO in maybeEmitSystemVal() at slang-emit-spirv.cpp:6210 and test file location
• ✅ Architecture Understanding: Learned how noperspective modifiers are represented using IRInterpolationModeDecoration with IRInterpolationMode::NoPerspective
• ✅ SPIRV Emission: Need to check for noperspective and emit SpvBuiltInBaryCoordNoPerspKHR (5287) instead of SpvBuiltInBaryCoordKHR (5286)
• ✅ GLSL Emission: Need to check for noperspective and use gl_BaryCoordNoPerspEXT instead of gl_BaryCoordEXT in getGLSLSystemValueInfo()

Next: Implementing the fixes...

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Job run | Branch: claude/issue-7816-20250718_051835

[davli-nv]

@claude for https://github.com/shader-slang/slang/tree/claude/issue-7816-20250718_051835 change the test such that a new input is added to existing shader that uses noperspective SV_Barycentrics and check the spirv decoration for both varying inputs, no need to add second shader

[github-actions]

Claude finished @davli-nv's task —— View job • claude/issue-7816-20250718_222155 • [Create PR ➔](https://github.com/shader-slang/slang/compare/master...claude/issue-7816-20250718_222155?quick_pull=1&title=Issue%20%237816%3A%20Changes%20from%20Claude&body=This%20PR%20addresses%20issue%20%237816%0A%0AGenerated%20with%20%5BClaude%20Code%5D(https%3A%2F%2Fclaude.ai%2Fcode)

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Working on modifying the test to add noperspective input to existing shader instead of creating a second shader...

Todo List

• Examine previous implementation in claude/issue-7816-20250718_051835 branch
• Understand current structure of get-attribute-at-vertex.slang test
• Apply SPIRV emission changes to current branch (maybeEmitSystemVal function)
• Apply GLSL emission changes to current branch (getGLSLSystemValueInfo function)
• Modify existing shader to add noperspective SV_Barycentrics input alongside regular one
• Update test CHECK statements to verify SPIRV decorations for both inputs
• Build and test the changes
• Debug why only one barycentric variable is being generated in SPIRV
• Fix the underlying issue with parameter sharing
• Commit and push the implementation

Progress:

• ✅ SPIRV & GLSL Emission: Successfully implemented the logic to detect noperspective interpolation and emit appropriate built-ins
• ✅ Test Changes: Modified shader to include both regular and noperspective barycentric inputs
• ✅ Build: Compilation successful
• ❌ Issue Found: Only one SPIRV variable is being generated with BuiltIn BaryCoordKHR, missing the BuiltIn BaryCoordNoPerspKHR

Root Cause Identified:

• The layout system treats parameters with the same semantic name as equivalent, regardless of interpolation modes
• Both parameters share the same layout (%18) and get mapped to the same global variable in SPIRV
• Modified BuiltinSpvVarKey to include interpolation mode to distinguish barycentric variables with different interpolation
• Added logic to extract interpolation mode from layout decorations when creating the key

Changes Made:

1. Enhanced BuiltinSpvVarKey (slang-emit-spirv.cpp:5859-5883): Added interpolationMode field to distinguish variables
2. Updated key construction (slang-emit-spirv.cpp:5932-5945): Extract interpolation mode for barycentric coordinates
3. SPIRV emission logic (slang-emit-spirv.cpp:6210-6230): Check noperspective mode and emit appropriate builtin
4. GLSL emission logic (slang-ir-glsl-legalize.cpp:862-886): Use correct GL extension for noperspective case
5. Test modifications: Added both regular and noperspective inputs to single shader with appropriate CHECK statements

Current Status: The architectural changes are in place but still debugging why both parameters map to the same variable. The issue appears to be that the parameter processing logic may not be calling maybeEmitSystemVal for both parameters separately due to layout sharing.

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Job run | Branch: claude/issue-7816-20250718_222155