Add SV_DrawIndex. (#5787)

Co-authored-by: Ellie Hermaszewska <ellieh@nvidia.com>

7 files changed, 36 insertions, 1 deletions

diff --git a/docs/user-guide/a2-01-spirv-target-specific.md b/docs/user-guide/a2-01-spirv-target-specific.md
index 048318a09..4faf3bde5 100644
--- a/docs/user-guide/a2-01-spirv-target-specific.md
+++ b/docs/user-guide/a2-01-spirv-target-specific.md
@@ -43,6 +43,7 @@ The system-value semantics are translated to the following SPIR-V code.
 | `SV_DepthLessEqual`           | `BuiltIn FragDepth`               |
 | `SV_DispatchThreadID`         | `BuiltIn GlobalInvocationId`      |
 | `SV_DomainLocation`           | `BuiltIn TessCoord`               |
+| `SV_DrawIndex`                | `Builtin DrawIndex`               |
 | `SV_GSInstanceID`             | `BuiltIn InvocationId`            |
 | `SV_GroupID`                  | `BuiltIn WorkgroupId`             |
 | `SV_GroupIndex`               | `BuiltIn LocalInvocationIndex`    |
@@ -68,7 +69,7 @@ The system-value semantics are translated to the following SPIR-V code.
 | `SV_ViewID`                   | `BuiltIn ViewIndex`               |
 | `SV_ViewportArrayIndex`       | `BuiltIn ViewportIndex`           |
 
-*Note* that `SV_PointSize` is a Slang-specific semantic that is not defined in HLSL.
+*Note* that `SV_DrawIndex` and `SV_PointSize` are Slang-specific semantics that are not defined in HLSL.
 
 
 Behavior of `discard` after SPIR-V 1.6
diff --git a/source/slang/slang-emit-glsl.cpp b/source/slang/slang-emit-glsl.cpp
index 6c525d064..f22419147 100644
--- a/source/slang/slang-emit-glsl.cpp
+++ b/source/slang/slang-emit-glsl.cpp
@@ -1127,6 +1127,10 @@ void GLSLSourceEmitter::_maybeEmitGLSLBuiltin(IRGlobalParam* var, UnownedStringS
     {
         _requireGLSLExtension(toSlice("GL_EXT_fragment_shading_rate_primitive"));
     }
+    else if (name == "gl_DrawID")
+    {
+        _requireGLSLVersion(460);
+    }
 }
 
 void GLSLSourceEmitter::_requireBaseType(BaseType baseType)
diff --git a/source/slang/slang-emit-spirv.cpp b/source/slang/slang-emit-spirv.cpp
index 58f5e4f66..f4aa900db 100644
--- a/source/slang/slang-emit-spirv.cpp
+++ b/source/slang/slang-emit-spirv.cpp
@@ -5137,6 +5137,11 @@ struct SPIRVEmitContext : public SourceEmitterBase, public SPIRVEmitSharedContex
                     // float in hlsl & glsl
                     return getBuiltinGlobalVar(inst->getFullType(), SpvBuiltInPointSize, inst);
                 }
+                else if (semanticName == "sv_drawindex")
+                {
+                    requireSPIRVCapability(SpvCapabilityDrawParameters);
+                    return getBuiltinGlobalVar(inst->getFullType(), SpvBuiltInDrawIndex, inst);
+                }
                 else if (semanticName == "sv_primitiveid")
                 {
                     auto entryPoints = m_referencingEntryPoints.tryGetValue(inst);
diff --git a/source/slang/slang-ir-glsl-legalize.cpp b/source/slang/slang-ir-glsl-legalize.cpp
index 3f3f2dbe0..619682692 100644
--- a/source/slang/slang-ir-glsl-legalize.cpp
+++ b/source/slang/slang-ir-glsl-legalize.cpp
@@ -623,6 +623,11 @@ GLSLSystemValueInfo* getGLSLSystemValueInfo(
         name = "gl_PointSize";
         requiredType = builder->getBasicType(BaseType::Float);
     }
+    else if (semanticName == "sv_drawindex")
+    {
+        name = "gl_DrawID";
+        requiredType = builder->getBasicType(BaseType::Int);
+    }
     else if (semanticName == "sv_primitiveid")
     {
         // uint in hlsl, int in glsl
diff --git a/source/slang/slang-ir-legalize-varying-params.h b/source/slang/slang-ir-legalize-varying-params.h
index 3c97d739b..c8952f604 100644
--- a/source/slang/slang-ir-legalize-varying-params.h
+++ b/source/slang/slang-ir-legalize-varying-params.h
@@ -48,6 +48,7 @@ IRInst* emitCalcGroupIndex(IRBuilder& builder, IRInst* groupThreadID, IRInst* gr
     M(OutputControlPointID, SV_OutputControlPointID)     \
     M(PointSize, SV_PointSize)                           \
     M(PrimitiveID, SV_PrimitiveID)                       \
+    M(DrawIndex, SV_DrawIndex)                           \
     M(RenderTargetArrayIndex, SV_RenderTargetArrayIndex) \
     M(SampleIndex, SV_SampleIndex)                       \
     M(StencilRef, SV_StencilRef)                         \
diff --git a/source/slang/slang-language-server-completion.cpp b/source/slang/slang-language-server-completion.cpp
index 82b7286ea..03c6b88ed 100644
--- a/source/slang/slang-language-server-completion.cpp
+++ b/source/slang/slang-language-server-completion.cpp
@@ -116,6 +116,7 @@ static const char* hlslSemanticNames[] = {
     "SV_Position",
     "SV_PointSize",
     "SV_PrimitiveID",
+    "SV_DrawIndex",
     "SV_RenderTargetArrayIndex",
     "SV_SampleIndex",
     "SV_StencilRef",
diff --git a/tests/spirv/draw-index.slang b/tests/spirv/draw-index.slang
new file mode 100644
index 000000000..9020eb8b4
--- /dev/null
+++ b/tests/spirv/draw-index.slang
@@ -0,0 +1,18 @@
+//TEST:SIMPLE(filecheck=SPIRV): -target spirv
+//TEST:SIMPLE(filecheck=SPIRV): -target spirv -entry vsMain -stage vertex -emit-spirv-via-glsl
+//TEST:SIMPLE(filecheck=GLSL): -target glsl -entry vsMain -stage vertex
+
+// SPIRV: OpDecorate %{{.*}} BuiltIn DrawIndex
+// GLSL: gl_DrawID
+
+struct VertexIn
+{
+    float3 position;
+    int drawIndex : SV_DrawIndex;
+}
+
+[shader("vertex")]
+float4 vsMain(VertexIn vin) : SV_Position
+{
+    return float4(vin.position, vin.drawIndex);
+}