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, 33 insertions, 0 deletions

diff --git a/tests/reflection/vertex-input-semantics.hlsl b/tests/reflection/vertex-input-semantics.hlsl
new file mode 100644
index 000000000..87a8431bc
--- /dev/null
+++ b/tests/reflection/vertex-input-semantics.hlsl
@@ -0,0 +1,33 @@
+//TEST:REFLECTION:-profile vs_4_0 -target hlsl
+
+// Confirm that we can generate reflection info for
+// vertex shader input parameters, including those
+// that have semantics, and including nesting
+// via struct types.
+
+struct X
+{
+	float4 x0;
+	float4 x1;
+};
+
+struct B
+{
+	int4 b0;
+	X b1;
+};
+
+struct C
+{
+	X c0 : CX;
+	int4 c1 : CY;
+};
+
+float4 main(
+	float4 a : A,
+	B b : B,
+	C c)
+	: SV_Position
+{
+	return 0.0;
+}
\ No newline at end of file