From 2bfccb1321e13799a600f3b92a25f59608397f35 Mon Sep 17 00:00:00 2001
From: baldurk <baldurk@baldurk.org>
Date: Thu, 5 Nov 2020 21:24:18 +0000
Subject: [PATCH] Properly apply vertexOffset for builtin in indexed draws

---
 renderdoc/driver/vulkan/vk_postvs.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/renderdoc/driver/vulkan/vk_postvs.cpp b/renderdoc/driver/vulkan/vk_postvs.cpp
index 49dd7ac1a..3f52bc3e9 100644
--- a/renderdoc/driver/vulkan/vk_postvs.cpp
+++ b/renderdoc/driver/vulkan/vk_postvs.cpp
@@ -894,6 +894,14 @@ static void ConvertToMeshOutputCompute(const ShaderReflection &refl, const SPIRV
           if(builtin == ShaderBuiltin::VertexIndex)
           {
             valueID = vertexIndexID;
+            // although for indexed draws we accounted for vertexOffset when looking up fixed
+            // function vertex inputs, we still need to apply it to the VertexIndex builtin here.
+            if(draw->flags & DrawFlags::Indexed)
+            {
+              valueID =
+                  ops.add(rdcspv::OpIAdd(uint32ID, editor.MakeId(), valueID,
+                                         editor.AddConstantImmediate<uint32_t>(draw->vertexOffset)));
+            }
           }
           else if(builtin == ShaderBuiltin::InstanceIndex)
           {