From 13ff0bd345990c0fdfb7b52ebd5339cddb04889e Mon Sep 17 00:00:00 2001
From: Tim Foley <tfoleyNV@users.noreply.github.com>
Date: Wed, 3 Mar 2021 11:45:39 -0800
Subject: 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.
---
 source/slang/hlsl.meta.slang | 12 ++++++++++++
 1 file changed, 12 insertions(+)

(limited to 'source/slang/hlsl.meta.slang')

diff --git a/source/slang/hlsl.meta.slang b/source/slang/hlsl.meta.slang
index adbe6f9c8..77b371662 100644
--- a/source/slang/hlsl.meta.slang
+++ b/source/slang/hlsl.meta.slang
@@ -1821,6 +1821,10 @@ matrix<T, N, M> fwidth(matrix<T, N, M> x)
 ///
 __generic<T : __BuiltinType>
 [__readNone]
+__target_intrinsic(hlsl)
+__target_intrinsic(glsl, "$0[$1]")
+__glsl_version(450)
+__glsl_extension(GL_NV_fragment_shader_barycentric)
 T GetAttributeAtVertex(T attribute, uint vertexIndex);
 
 /// Get the value of a vertex attribute at a specific vertex.
@@ -1839,6 +1843,10 @@ T GetAttributeAtVertex(T attribute, uint vertexIndex);
 ///
 __generic<T : __BuiltinType, let N : int>
 [__readNone]
+__target_intrinsic(hlsl)
+__target_intrinsic(glsl, "$0[$1]")
+__glsl_version(450)
+__glsl_extension(GL_NV_fragment_shader_barycentric)
 vector<T,N> GetAttributeAtVertex(vector<T,N> attribute, uint vertexIndex);
 
 /// Get the value of a vertex attribute at a specific vertex.
@@ -1857,6 +1865,10 @@ vector<T,N> GetAttributeAtVertex(vector<T,N> attribute, uint vertexIndex);
 ///
 __generic<T : __BuiltinType, let N : int, let M : int>
 [__readNone]
+__target_intrinsic(hlsl)
+__target_intrinsic(glsl, "$0[$1]")
+__glsl_version(450)
+__glsl_extension(GL_NV_fragment_shader_barycentric)
 matrix<T,N,M> GetAttributeAtVertex(matrix<T,N,M> attribute, uint vertexIndex);
 
 
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