From c79d939445993666d2355079f5a38fe4c00e7ab0 Mon Sep 17 00:00:00 2001
From: baldurk <baldurk@baldurk.org>
Date: Tue, 5 May 2026 18:00:28 +0100
Subject: [PATCH] Add manual emulation of IsHelperLane() on SM <6.6

* The default dxc emulation does not work when running in MSAA as our shader
  runs at sample rate and SV_Coverage can be non-zero even for helper lanes.
---
 renderdoc/driver/shaders/dxbc/dx_debug.cpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/renderdoc/driver/shaders/dxbc/dx_debug.cpp b/renderdoc/driver/shaders/dxbc/dx_debug.cpp
index d9cd245cd..59787aa7f 100644
--- a/renderdoc/driver/shaders/dxbc/dx_debug.cpp
+++ b/renderdoc/driver/shaders/dxbc/dx_debug.cpp
@@ -964,7 +964,13 @@ void ExtractInputs(Inputs IN
 
   quadLaneIndex = (2u * (uint(debug_pixelPos.y) & 1u)) + (uint(debug_pixelPos.x) & 1u);
   derivValid = ddx(debug_pixelPos.x);
+
+#if __SHADER_TARGET_MINOR >= 6
+  // IsHelperLane() can fail when software emulated on MSAA, because it checks SV_Coverage != 0
   isHelper = IsHelperLane() ? 1 : 0;
+#else
+  isHelper = (coverage & (1u << sample)) == 0;
+#endif
 
   helperBallot = WaveActiveBallot(isHelper != 0);