Handle `flat` interpolation cases in cross compilation

Fixes #104

- Map HLSL `nointerpolation` to GLSL `flat`

- When lowering a `struct` type varying input/output, look for interpolation modifiers along the "chain" from the leaf field up to the original shader input variable (and take the first one found)
  - Not sure if this is strictly needed, but it seems like a reasonable policy

- Add `flat` to varying input of integer type, with no other interpolation modifier
  - Note: I do *not* do anything to ignore a manually imposed interpolation modifier that might be incorrect

1 files changed, 3 insertions, 2 deletions

diff --git a/source/slang/emit.cpp b/source/slang/emit.cpp
index 88b80589a..7ffce2acd 100644
--- a/source/slang/emit.cpp
+++ b/source/slang/emit.cpp
@@ -2667,11 +2667,12 @@ struct EmitVisitor
                 else if(auto mod_##TYPE = mod.As<TYPE>()) Emit(#KEYWORD " ")
 
             #define CASE2(TYPE, HLSL_NAME, GLSL_NAME) \
-                else if(auto mod_##TYPE = mod.As<TYPE>()) Emit((context->shared->target == CodeGenTarget::GLSL) ? GLSL_NAME : HLSL_NAME)
+                else if(auto mod_##TYPE = mod.As<TYPE>()) Emit((context->shared->target == CodeGenTarget::GLSL) ? (#GLSL_NAME " ") : (#HLSL_NAME " "))
 
             CASE(RowMajorLayoutModifier, row_major);
             CASE(ColumnMajorLayoutModifier, column_major);
-            CASE(HLSLNoInterpolationModifier, nointerpolation);
+
+            CASE2(HLSLNoInterpolationModifier, nointerpolation, flat);
             CASE(HLSLPreciseModifier, precise);
             CASE(HLSLEffectSharedModifier, shared);
             CASE(HLSLGroupSharedModifier, groupshared);