Implement SPV_EXT_fragment_invocation_density (SPV_NV_shading_rate) (#8037)

* Implement SPV_EXT_fragment_invocation_density

-Adds semantics SV_FragSize and SV_FragInvocationCount and implements them for SPIRV and GLSL using the appropriate target builtins from extensions.
-Adds test case checking for expected target builtins from these semantics.
-For future work, could implement SV_FragSize using pixel shader input SV_ShadingRate for HLSL, and SV_FragInvocationCount needs research.

Fixes #7974

Generated with Claude Code

* address review feedback

https://github.com/shader-slang/slang/pull/8037#pullrequestreview-3084645845

* fixup format

* review feedback

https://github.com/shader-slang/slang/pull/8037#pullrequestreview-3086442819

1 files changed, 8 insertions, 0 deletions

diff --git a/source/slang/slang-emit-glsl.cpp b/source/slang/slang-emit-glsl.cpp
index eb71286a2..eb6d4c694 100644
--- a/source/slang/slang-emit-glsl.cpp
+++ b/source/slang/slang-emit-glsl.cpp
@@ -1246,6 +1246,14 @@ void GLSLSourceEmitter::_maybeEmitGLSLBuiltin(IRGlobalParam* var, UnownedStringS
     {
         _requireGLSLExtension(toSlice("GL_EXT_fragment_shading_rate_primitive"));
     }
+    else if (name == "gl_FragSizeEXT")
+    {
+        _requireGLSLExtension(toSlice("GL_EXT_fragment_invocation_density"));
+    }
+    else if (name == "gl_FragInvocationCountEXT")
+    {
+        _requireGLSLExtension(toSlice("GL_EXT_fragment_invocation_density"));
+    }
     else if (name == "gl_DrawID")
     {
         _requireGLSLVersion(460);