From 79dfafc69176ef8f215931c768cfd7113eefa014 Mon Sep 17 00:00:00 2001
From: spherallic <spherallic@gmail.com>
Date: Tue, 9 May 2023 20:45:25 +0200
Subject: [PATCH] Correct sector references when manually flipping sidedefs

---
 Source/Core/Map/Linedef.cs                            | 11 ++++++++++-
 .../Plugins/BuilderModes/ClassicModes/LinedefsMode.cs |  2 +-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/Source/Core/Map/Linedef.cs b/Source/Core/Map/Linedef.cs
index 3239cfd..79fb2e8 100644
--- a/Source/Core/Map/Linedef.cs
+++ b/Source/Core/Map/Linedef.cs
@@ -1014,13 +1014,22 @@ namespace CodeImp.DoomBuilder.Map
 		}
 
 		// This flips the sidedefs
-		public void FlipSidedefs()
+		public void FlipSidedefs() { FlipSidedefs(false); }
+		
+		public void FlipSidedefs(bool flipsectorrefs)
 		{
 			// Flip sidedefs
 			Sidedef oldfront = front;
 			Sidedef oldback = back;
 			AttachFront(oldback);
 			AttachBack(oldfront);
+
+			if (flipsectorrefs & back != null)
+			{
+				Sector old = back.Sector;
+				back.SetSector(front.Sector);
+				front.SetSector(old);
+			}
 			
 			General.Map.IsChanged = true;
 		}
diff --git a/Source/Plugins/BuilderModes/ClassicModes/LinedefsMode.cs b/Source/Plugins/BuilderModes/ClassicModes/LinedefsMode.cs
index d25acb5..e3d1c5b 100644
--- a/Source/Plugins/BuilderModes/ClassicModes/LinedefsMode.cs
+++ b/Source/Plugins/BuilderModes/ClassicModes/LinedefsMode.cs
@@ -2110,7 +2110,7 @@ namespace CodeImp.DoomBuilder.BuilderModes
 			// Flip sidedefs in all selected linedefs
 			foreach(Linedef l in validlines) 
 			{
-				l.FlipSidedefs();
+				l.FlipSidedefs(true);
 				l.Front.Sector.UpdateNeeded = true;
 				l.Back.Sector.UpdateNeeded = true;
 			}