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, 17 insertions, 0 deletions

diff --git a/source/slang/slang-emit-spirv.cpp b/source/slang/slang-emit-spirv.cpp
index da2620856..a5a77e148 100644
--- a/source/slang/slang-emit-spirv.cpp
+++ b/source/slang/slang-emit-spirv.cpp
@@ -6226,6 +6226,23 @@ struct SPIRVEmitContext : public SourceEmitterBase, public SPIRVEmitSharedContex
                         SpvBuiltInCullPrimitiveEXT,
                         inst);
                 }
+                else if (semanticName == "sv_fragsize")
+                {
+                    requireSPIRVCapability(SpvCapabilityFragmentDensityEXT);
+                    ensureExtensionDeclaration(
+                        UnownedStringSlice("SPV_EXT_fragment_invocation_density"));
+                    return getBuiltinGlobalVar(inst->getFullType(), SpvBuiltInFragSizeEXT, inst);
+                }
+                else if (semanticName == "sv_fraginvocationcount")
+                {
+                    requireSPIRVCapability(SpvCapabilityFragmentDensityEXT);
+                    ensureExtensionDeclaration(
+                        UnownedStringSlice("SPV_EXT_fragment_invocation_density"));
+                    return getBuiltinGlobalVar(
+                        inst->getFullType(),
+                        SpvBuiltInFragInvocationCountEXT,
+                        inst);
+                }
                 else if (semanticName == "sv_shadingrate")
                 {
                     requireSPIRVCapability(SpvCapabilityFragmentShadingRateKHR);