From 2a45bc312d9e4d2bc7d4ef0f172dd54750133b35 Mon Sep 17 00:00:00 2001
From: Yong He <yonghe@outlook.com>
Date: Fri, 7 Jun 2024 21:42:45 -0700
Subject: Support HLSL `.mips` syntax. (#4310)

---
 source/slang/hlsl.meta.slang           | 31 +++++++++++++++++++++++++++++++
 tests/hlsl/texture-mips-operator.slang | 13 +++++++++++++
 2 files changed, 44 insertions(+)
 create mode 100644 tests/hlsl/texture-mips-operator.slang

diff --git a/source/slang/hlsl.meta.slang b/source/slang/hlsl.meta.slang
index defb27ce3..f9831bef2 100644
--- a/source/slang/hlsl.meta.slang
+++ b/source/slang/hlsl.meta.slang
@@ -3050,6 +3050,37 @@ ${{{{
 } // for (access).
 }}}}
 
+// Definitions to support the legacy texture .mips[][] operator.
+struct __TextureMip<T, Shape : __ITextureShape, let isArray : int, let isCombined : int, let format : int>
+{
+    __TextureImpl<T, Shape, isArray, 0 /*isMS*/, 0 /*sampleCount*/, 0 /*access*/, 0 /*isShadow*/, isCombined, format> tex;
+    int mip;
+    __subscript(vector<int, isArray + Shape.dimensions> pos)->T
+    {
+        [__unsafeForceInlineEarly]
+        get { return tex.Load(__makeVector(pos, mip)); }
+    }
+}
+struct __TextureMips<T, Shape : __ITextureShape, let isArray : int, let isCombined : int, let format : int>
+{
+    __TextureImpl<T, Shape, isArray, 0 /*isMS*/, 0 /*sampleCount*/, 0 /*access*/, 0 /*isShadow*/, isCombined, format> tex;
+    __subscript(int mip)->__TextureMip<T, Shape, isArray, isCombined, format>
+    {
+        [__unsafeForceInlineEarly]
+        get { return { tex, mip }; }
+    }
+}
+
+__generic<T, Shape : __ITextureShape, let isArray : int, let isCombined : int, let format : int>
+extension __TextureImpl<T, Shape, isArray, 0 /*isMS*/, 0 /*sampleCount*/, 0 /*access*/, 0 /*isShadow*/, isCombined, format>
+{
+    property __TextureMips<T, Shape, isArray, isCombined, format> mips
+    {
+        [__unsafeForceInlineEarly]
+        get { return { this }; }
+    }
+}
+
 // Texture type aliases.
 // T, Shape: __ITextureShape, let isArray:int, let isMS:int, let sampleCount:int, let access:int, let isShadow:int, let isCombined:int, let format:int
 ${{{{
diff --git a/tests/hlsl/texture-mips-operator.slang b/tests/hlsl/texture-mips-operator.slang
new file mode 100644
index 000000000..9da8711c5
--- /dev/null
+++ b/tests/hlsl/texture-mips-operator.slang
@@ -0,0 +1,13 @@
+//TEST:SIMPLE(filecheck=CHECK): -target spirv
+
+// CHECK: OpImageFetch %v4float {{.*}} Lod %int_1
+
+RWStructuredBuffer<float4> result;
+
+uniform Texture2D gTex;
+
+[numthreads(1,1,1)]
+void main()
+{
+    result[0] = gTex.mips[1][int2(3,4)];
+}
\ No newline at end of file
-- 
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