From 6e70f36134326ba3a824c019d7d54fcd2ca1d671 Mon Sep 17 00:00:00 2001
From: Geoffrey McRae <geoff@hostfission.com>
Date: Sat, 18 Jul 2026 04:01:19 +1000
Subject: [PATCH] [idd] never add the extraMode to the EDID

Doing so causes windows to treat a new EDID as a new monitor
---
 idd/LGIdd/CEdid.cpp     | 8 ++++++++
 idd/LGIdd/CSettings.cpp | 8 +++++++-
 idd/LGIdd/CSettings.h   | 1 +
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/idd/LGIdd/CEdid.cpp b/idd/LGIdd/CEdid.cpp
index f9fbfc8a..c23fa60b 100644
--- a/idd/LGIdd/CEdid.cpp
+++ b/idd/LGIdd/CEdid.cpp
@@ -554,6 +554,10 @@ void CEdid::Build(const CSettings::DisplayModes& modes)
     baseDtdIndex < EDID_BASE_DETAILED_TIMING_COUNT;
     ++modeIndex)
   {
+    // never include the extra mode in the EDID
+    if (sorted[modeIndex].extraMode)
+      continue;
+
     if (MakeDetailedTiming(
       baseBlock.descriptors[baseDtdIndex].detailedTiming,
       sorted[modeIndex]))
@@ -589,6 +593,10 @@ void CEdid::Build(const CSettings::DisplayModes& modes)
     ctaDtdWrite + EDID_DTD_SIZE <= EDID_BLOCK_SIZE - 1;
     ++modeIndex)
   {
+    // never include the extra mode in the EDID
+    if (sorted[modeIndex].extraMode)
+      continue;
+
     if (WriteDetailedTiming(cta + ctaDtdWrite, sorted[modeIndex]))
       ctaDtdWrite += EDID_DTD_SIZE;
   }
diff --git a/idd/LGIdd/CSettings.cpp b/idd/LGIdd/CSettings.cpp
index f1256cc6..4e38d227 100644
--- a/idd/LGIdd/CSettings.cpp
+++ b/idd/LGIdd/CSettings.cpp
@@ -58,6 +58,7 @@ void CSettings::LoadModes()
       m.height    = DefaultDisplayModes[i][1];
       m.refresh   = defaultRefresh;
       m.preferred = !hasPreferred && (i == DefaultPreferredDisplayMode);
+      m.extraMode = false;
       m_displayModes.push_back(m);
     }
     return;
@@ -209,7 +210,11 @@ bool CSettings::GetExtraMode(DisplayMode& mode)
   if (extraMode.empty())
     return false;
 
-  return ParseModeString(extraMode, mode);
+  if (!ParseModeString(extraMode, mode))
+    return false;
+
+  mode.extraMode = true;
+  return true;
 }
 
 unsigned CSettings::GetDefaultRefresh() const
@@ -318,5 +323,6 @@ bool CSettings::ParseModeString(const std::wstring& in, DisplayMode& out)
       out.refresh > 1000)
     return false;
 
+  out.extraMode = false;
   return true;
 }
diff --git a/idd/LGIdd/CSettings.h b/idd/LGIdd/CSettings.h
index 2137a916..a391da52 100644
--- a/idd/LGIdd/CSettings.h
+++ b/idd/LGIdd/CSettings.h
@@ -32,6 +32,7 @@ class CSettings
       unsigned height;
       unsigned refresh;
       bool     preferred;
+      bool     extraMode;
     };
     typedef std::vector<DisplayMode> DisplayModes;