Add GLSL/SPIR-V support got GetAttributeAtVertex (#1733)

This change allows varying fragment shader inputs to be declared in a way that allows the `GetAttributeAtVertex` operation to compile to valid code for both D3D and GLSL/SPIR-V/Vulkan.

The key is that rather than just use ordinary `nointerpolation`-qualified inputs the code must declare these varying inputs with a new `pervertex` qualifier that marks them as *only* being usable with `GetAttributeAtVertex`. The `pervertex`-tagged inputs then translate to GLSL inputs using the `pervertexNV` qualifier

Note that this change does *not* include any enforcement of the requirements around how these qualifiers are used (and the compiler doesn't have enforcement for the existing operations like `EvaluateAttributeAtCentroid`). The underlying problem is that the inerpolation-mode qualifiers and explicit interpolation functions in HLSL constitute a kind of rate-qualified type system, but without any systematic rules. It seems wasteful to encode a bunch of ad hoc rules for this stuff as special cases in the compiler when the clear right answer is to implement a systematic approach to rates.

2 files changed, 27 insertions, 1 deletions

diff --git a/tests/pipeline/rasterization/get-attribute-at-vertex.slang b/tests/pipeline/rasterization/get-attribute-at-vertex.slang
index 56fbcce78..87d39c806 100644
--- a/tests/pipeline/rasterization/get-attribute-at-vertex.slang
+++ b/tests/pipeline/rasterization/get-attribute-at-vertex.slang
@@ -3,10 +3,11 @@
 // Basic test for `GetAttributeAtVertex` function
 
 //TEST:CROSS_COMPILE:-target dxil -entry main -stage fragment -profile sm_6_1
+//TEST:CROSS_COMPILE:-target spirv -entry main -stage fragment -profile glsl_450
 
 [shader("fragment")]
 void main(
-    nointerpolation float4 color : COLOR,
+    pervertex float4 color : COLOR,
     float3 bary : SV_Barycentrics,
     out float4 result : SV_Target)
 {
diff --git a/tests/pipeline/rasterization/get-attribute-at-vertex.slang.glsl b/tests/pipeline/rasterization/get-attribute-at-vertex.slang.glsl
new file mode 100644
index 000000000..c07e9b61c
--- /dev/null
+++ b/tests/pipeline/rasterization/get-attribute-at-vertex.slang.glsl
@@ -0,0 +1,25 @@
+// get-attribute-at-vertex.slang.glsl
+//TEST_IGNORE_FILE:
+
+#version 450
+
+#extension GL_NV_fragment_shader_barycentric : require
+
+pervertexNV layout(location = 0)
+in vec4 _S1[3];
+
+layout(location = 0)
+out vec4 _S2;
+
+void main()
+{
+    vec4 _S3;
+
+    _S3 = gl_BaryCoordNV.x * _S1[0]
+        + gl_BaryCoordNV.y * _S1[1]
+        + gl_BaryCoordNV.z * _S1[2];
+
+    _S2 = _S3;
+
+    return;
+}