diff --git a/src/gl/data/gl_vertexbuffer.cpp b/src/gl/data/gl_vertexbuffer.cpp
index 4973ad39d..957884bb0 100644
--- a/src/gl/data/gl_vertexbuffer.cpp
+++ b/src/gl/data/gl_vertexbuffer.cpp
@@ -397,7 +397,9 @@ void FFlatVertexBuffer::CreateFlatVBO()
 	{
 		for(auto &sec : level.sectors)
 		{
-			CreateVertices(h, &sec, sec.GetSecPlane(h), h == sector_t::floor);
+			secplane_t& plane = sec.GetSecPlane(h);
+			CreateVertices(h, &sec, plane, h == sector_t::floor);
+			plane.vbonormal = plane.normal;
 		}
 	}
 
@@ -464,15 +466,21 @@ void FFlatVertexBuffer::CreateVBO()
 
 void FFlatVertexBuffer::CheckPlanes(sector_t *sector)
 {
-	if (sector->GetPlaneTexZ(sector_t::ceiling) != sector->vboheight[sector_t::ceiling])
+	for (int i = sector_t::floor; i <= sector_t::ceiling; i++)
 	{
-		UpdatePlaneVertices(sector, sector_t::ceiling);
-		sector->vboheight[sector_t::ceiling] = sector->GetPlaneTexZ(sector_t::ceiling);
-	}
-	if (sector->GetPlaneTexZ(sector_t::floor) != sector->vboheight[sector_t::floor])
-	{
-		UpdatePlaneVertices(sector, sector_t::floor);
-		sector->vboheight[sector_t::floor] = sector->GetPlaneTexZ(sector_t::floor);
+		if (sector->GetPlaneTexZ(i) != sector->vboheight[i])
+		{
+			UpdatePlaneVertices(sector, i);
+			sector->vboheight[i] = sector->GetPlaneTexZ(i);
+			continue;
+		}
+
+		secplane_t &splane = sector->GetSecPlane(i);
+		if (splane.normal != splane.vbonormal)
+		{
+			UpdatePlaneVertices(sector, i);
+			splane.vbonormal = splane.normal;
+		}
 	}
 }
 
diff --git a/src/p_map.cpp b/src/p_map.cpp
index 50397d852..6767c2f5f 100644
--- a/src/p_map.cpp
+++ b/src/p_map.cpp
@@ -6757,6 +6757,21 @@ void PIT_CeilingRaise(AActor *thing, FChangePosition *cpos)
 //
 //=============================================================================
 
+//
+DEFINE_ACTION_FUNCTION(_Sector, ChangeSector)
+{
+	PARAM_SELF_STRUCT_PROLOGUE(sector_t);
+	PARAM_INT(crunch);
+	PARAM_FLOAT(amt);
+	PARAM_INT(floorOrCeil);
+	PARAM_BOOL(isreset);
+	PARAM_BOOL(instant);
+
+	bool b = P_ChangeSector(self, crunch, amt, floorOrCeil, isreset, instant);
+
+	ACTION_RETURN_BOOL(b);
+}
+
 bool P_ChangeSector(sector_t *sector, int crunch, double amt, int floorOrCeil, bool isreset, bool instant)
 {
 	FChangePosition cpos;
diff --git a/src/r_defs.h b/src/r_defs.h
index 6a3dfac76..910025d33 100644
--- a/src/r_defs.h
+++ b/src/r_defs.h
@@ -288,6 +288,7 @@ struct secplane_t
 //private:
 	DVector3 normal;
 	double  D, negiC;	// negative iC because that also saves a negation in all methods using this.
+	DVector3 vbonormal; // [ZZ] for opengl update. it's critical that this member is the last one, so that {{x,y,z},...} works properly
 public:
 	friend FSerializer &Serialize(FSerializer &arc, const char *key, secplane_t &p, secplane_t *def);
 
diff --git a/wadsrc/static/zscript/mapdata.txt b/wadsrc/static/zscript/mapdata.txt
index 011400f86..a1f4ad966 100644
--- a/wadsrc/static/zscript/mapdata.txt
+++ b/wadsrc/static/zscript/mapdata.txt
@@ -314,7 +314,7 @@ struct Sector native play
 		SECF_NOMODIFY = SECF_SECRET|SECF_WASSECRET,	// not modifiable by Sector_ChangeFlags
 		SECF_SPECIALFLAGS = SECF_DAMAGEFLAGS|SECF_FRICTION|SECF_PUSH,	// these flags originate from 'special and must be transferrable by floor thinkers
 	}
-	
+
 	enum EMoveResult 
 	{ 
 		MOVE_OK, 
@@ -333,6 +333,15 @@ struct Sector native play
 
 	native int Index();
 
+	enum EChangeSectorMode
+	{
+		CS_Floor = 0,
+		CS_Ceiling = 1,
+		CS_3DMidTex = 2
+	};
+
+	native bool ChangeSector(int crunch, double amt, EChangeSectorMode mode/*floorOrCeiling*/, bool isreset, bool instant);
+
 	native double, Sector, F3DFloor NextHighestCeilingAt(double x, double y, double bottomz, double topz, int flags = 0);
 	native double, Sector, F3DFloor NextLowestFloorAt(double x, double y, double z, int flags = 0, double steph = 0);