Reflection: allow querying of semantics on varying input/output (#224)

This is functionality required to support a Falcor bug fix.

Most of the code to compute the right semantic name/index for a parameter was already present.
This change adds:

- Storage for semantic name/index on every `VarLayout`
  - Note: this is wasteful and should be optimized later

- A public API to query the semantic name/index
  - The contract is that this API returns `NULL` if the parameter had no semantic

- A bit of work in `parameter-binding.cpp` to attach semantics to varying input/output when traversing varying parameters.
  - Note: this is intentionally set up so that it associates semantics even with non-leaf parameters, so that an API user can query the semantic of a `struct` parameter and know that its members will be assigned sequential semantic indices from its starting value.

- Support for dumping this information in reflection tests

One notable thing that I did *not* change here is that the reflection test fixture doesn't report information on the output of an entry point, even though it really should. That should be fixed in a separate change, though, because it would affect many of the expected outputs.

1 files changed, 22 insertions, 0 deletions

diff --git a/source/slang/reflection.cpp b/source/slang/reflection.cpp
index 435b4db3f..d7e8820c0 100644
--- a/source/slang/reflection.cpp
+++ b/source/slang/reflection.cpp
@@ -623,6 +623,28 @@ SLANG_API size_t spReflectionVariableLayout_GetSpace(SlangReflectionVariableLayo
     return info->space;
 }
 
+SLANG_API char const* spReflectionVariableLayout_GetSemanticName(SlangReflectionVariableLayout* inVarLayout)
+{
+    auto varLayout = convert(inVarLayout);
+    if(!varLayout) return 0;
+
+    if (!(varLayout->flags & Slang::VarLayoutFlag::HasSemantic))
+        return 0;
+
+    return varLayout->semanticName.Buffer();
+}
+
+SLANG_API size_t spReflectionVariableLayout_GetSemanticIndex(SlangReflectionVariableLayout* inVarLayout)
+{
+    auto varLayout = convert(inVarLayout);
+    if(!varLayout) return 0;
+
+    if (!(varLayout->flags & Slang::VarLayoutFlag::HasSemantic))
+        return 0;
+
+    return varLayout->semanticIndex;
+}
+
 
 // Shader Parameter Reflection