Adjust type layout when parameter block constains member using the same resource

If we have something like to following in HLSL:

    cbuffer C { Texture2D t; ... }

and we are compiling to GLSL, then both `C` and `C.t` consume the same kind of resource (a descriptor-table slot).
The way reflection was working right now, querying the index of `C` would return its binding (let's say it is `4` just to be concrete) and then a query on `C::t` would give its offset, which was being computed as `0` because it is the first field in the logical `struct` type.

That obviously leads to bad math and requires some subtle `+1`s in cases to get things right (e.g., when scalaring during lowering, I had to carefully add one in some cases).
It is unreasonable to expect users to deal with this.

This commit changes it so that the offset of field `C::t` is `1` so that hopefully more things Just Work.
The special-case logic in lowering is now gone.

One important catch here is that this pretty much only works in the case where the element type of a parameter block is a `struct` type (which is really all that makes sense right now).
If we ever want to generalize this in the future, then it will probably be necessary to change the `TypeLayout` case for parameter blocks to store a `VarLayout` for the element, rather than just a `TypeLayout`.

1 files changed, 3 insertions, 2 deletions

diff --git a/source/slang/parameter-binding.cpp b/source/slang/parameter-binding.cpp
index 01727fb36..007c023e2 100644
--- a/source/slang/parameter-binding.cpp
+++ b/source/slang/parameter-binding.cpp
@@ -1342,8 +1342,9 @@ void generateParameterBindings(
     {
         auto globalConstantBufferLayout = createParameterBlockTypeLayout(
             nullptr,
-            globalScopeStructLayout,
-            globalScopeRules);
+            globalScopeRules,
+            globalScopeRules->GetObjectLayout(ShaderParameterKind::ConstantBuffer),
+            globalScopeStructLayout);
 
         globalScopeLayout = globalConstantBufferLayout;
     }