diff --git a/src/gl/compatibility/gl_20.cpp b/src/gl/compatibility/gl_20.cpp
index 0f75ba4676..18d96c9b28 100644
--- a/src/gl/compatibility/gl_20.cpp
+++ b/src/gl/compatibility/gl_20.cpp
@@ -588,6 +588,7 @@ bool FDrawInfo::PutFlatCompat(GLFlat *flat, bool fog)
 	int list = list_indices[masked][foggy];
 	auto newflat = dldrawlists[list].NewFlat();
 	*newflat = *flat;
+	newflat->vboindex = -1;	// don't use the vertex buffer with legacy lights to ensure all passes use the same render logic.
 	return true;
 }
 
diff --git a/src/gl/data/gl_vertexbuffer.cpp b/src/gl/data/gl_vertexbuffer.cpp
index 335c7740ca..cd7549aa8a 100644
--- a/src/gl/data/gl_vertexbuffer.cpp
+++ b/src/gl/data/gl_vertexbuffer.cpp
@@ -125,6 +125,8 @@ void FSimpleVertexBuffer::set(FSimpleVertex *verts, int count)
 FFlatVertexBuffer::FFlatVertexBuffer(int width, int height)
 : FVertexBuffer(!gl.legacyMode), FFlatVertexGenerator(width, height)
 {
+	ibo_id = 0;
+	if (gl.buffermethod != BM_LEGACY) glGenBuffers(1, &ibo_id);
 	switch (gl.buffermethod)
 	{
 	case BM_PERSISTENT:
@@ -171,6 +173,11 @@ FFlatVertexBuffer::~FFlatVertexBuffer()
 		glUnmapBuffer(GL_ARRAY_BUFFER);
 		glBindBuffer(GL_ARRAY_BUFFER, 0);
 	}
+	if (ibo_id != 0)
+	{
+		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
+		glDeleteBuffers(1, &ibo_id);
+	}
 	if (gl.legacyMode)
 	{
 		delete[] map;
@@ -189,6 +196,7 @@ void FFlatVertexBuffer::OutputResized(int width, int height)
 void FFlatVertexBuffer::BindVBO()
 {
 	glBindBuffer(GL_ARRAY_BUFFER, vbo_id);
+	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo_id);
 	if (!gl.legacyMode)
 	{
 		glVertexAttribPointer(VATTR_VERTEX, 3, GL_FLOAT, false, sizeof(FFlatVertex), &VTO->x);
@@ -246,4 +254,9 @@ void FFlatVertexBuffer::CreateVBO()
 	Map();
 	memcpy(map, &vbo_shadowdata[0], vbo_shadowdata.Size() * sizeof(FFlatVertex));
 	Unmap();
+	if (ibo_id > 0)
+	{
+		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo_id);
+		glBufferData(GL_ELEMENT_ARRAY_BUFFER, ibo_data.Size() * sizeof(uint32_t), &ibo_data[0], GL_STATIC_DRAW);
+	}
 }
diff --git a/src/gl/data/gl_vertexbuffer.h b/src/gl/data/gl_vertexbuffer.h
index de741b2511..7c54b1916e 100644
--- a/src/gl/data/gl_vertexbuffer.h
+++ b/src/gl/data/gl_vertexbuffer.h
@@ -95,6 +95,7 @@ public:
 
 class FFlatVertexBuffer : public FVertexBuffer, public FFlatVertexGenerator
 {
+	unsigned int ibo_id;
 	FFlatVertex *map;
 	unsigned int mIndex;
 	std::atomic<unsigned int> mCurIndex;
@@ -177,6 +178,11 @@ public:
 
 #endif
 
+	uint32_t *GetIndexPointer() const
+	{
+		return ibo_id == 0 ? &ibo_data[0] : nullptr;
+	}
+
 	void Reset()
 	{
 		mCurIndex = mIndex;
diff --git a/src/gl/renderer/gl_renderstate.cpp b/src/gl/renderer/gl_renderstate.cpp
index 305a5177cc..a0a1c5cc81 100644
--- a/src/gl/renderer/gl_renderstate.cpp
+++ b/src/gl/renderer/gl_renderstate.cpp
@@ -62,7 +62,7 @@ static void matrixToGL(const VSMatrix &mat, int loc)
 void FRenderState::Reset()
 {
 	mTextureEnabled = true;
-	mClipLineEnabled = mSplitEnabled = mBrightmapEnabled = mFogEnabled = mGlowEnabled = false;
+	mClipLineShouldBeActive = mClipLineEnabled = mSplitEnabled = mBrightmapEnabled = mFogEnabled = mGlowEnabled = false;
 	mColorMask[0] = mColorMask[1] = mColorMask[2] = mColorMask[3] = true;
 	currentColorMask[0] = currentColorMask[1] = currentColorMask[2] = currentColorMask[3] = true;
 	mFogColor.d = -1;
diff --git a/src/gl/renderer/gl_renderstate.h b/src/gl/renderer/gl_renderstate.h
index 1db6602a57..8aa4d00938 100644
--- a/src/gl/renderer/gl_renderstate.h
+++ b/src/gl/renderer/gl_renderstate.h
@@ -81,6 +81,7 @@ class FRenderState
 	bool mGlowEnabled;
 	bool mSplitEnabled;
 	bool mClipLineEnabled;
+	bool mClipLineShouldBeActive;
 	bool mBrightmapEnabled;
 	bool mColorMask[4];
 	bool currentColorMask[4];
@@ -201,6 +202,11 @@ public:
 		return mClipLineEnabled;
 	}
 
+	bool GetClipLineShouldBeActive()
+	{
+		return mClipLineShouldBeActive;
+	}
+
 	void SetClipHeight(float height, float direction);
 
 	void SetNormal(FVector3 norm)
@@ -326,6 +332,11 @@ public:
 				glDisable(GL_CLIP_DISTANCE0);
 			}
 		}
+		else
+		{
+			// this needs to be flagged because in this case per-sector plane rendering needs to be disabled if a clip plane is active.
+			mClipLineShouldBeActive = on;
+		}
 	}
 
 	void EnableBrightmap(bool on)
diff --git a/src/gl/scene/gl_drawinfo.h b/src/gl/scene/gl_drawinfo.h
index 4ab217babb..8da945e6c6 100644
--- a/src/gl/scene/gl_drawinfo.h
+++ b/src/gl/scene/gl_drawinfo.h
@@ -121,6 +121,7 @@ struct FDrawInfo : public HWDrawInfo
 	void ProcessLights(GLFlat *flat, bool istrans);
 	void DrawSubsector(GLFlat *flat, subsector_t * sub);
 	void SetupSubsectorLights(GLFlat *flat, int pass, subsector_t * sub, int *dli);
+	void SetupSectorLights(GLFlat *flat, int pass, int *dli);
 
 	// Sprite drawer
 	void DrawSprite(GLSprite *sprite, int pass);
diff --git a/src/gl/scene/gl_flats.cpp b/src/gl/scene/gl_flats.cpp
index 380271989c..0aa9c88fc4 100644
--- a/src/gl/scene/gl_flats.cpp
+++ b/src/gl/scene/gl_flats.cpp
@@ -48,6 +48,8 @@
 #include "gl/scene/gl_scenedrawer.h"
 #include "gl/renderer/gl_quaddrawer.h"
 
+CVAR(Bool, gl_render_subsectors, false, 0)
+
 //==========================================================================
 //
 // Flats 
@@ -62,7 +64,35 @@ void FDrawInfo::SetupSubsectorLights(GLFlat *flat, int pass, subsector_t * sub,
 		(*dli)++;
 		return;
 	}
-	if (flat->SetupSubsectorLights(pass, sub, lightdata))
+	if (flat->SetupSectorLights(pass, flat->sector, lightdata))
+	{
+		int d = GLRenderer->mLights->UploadLights(lightdata);
+		if (pass == GLPASS_LIGHTSONLY)
+		{
+			GLRenderer->mLights->StoreIndex(d);
+		}
+		else
+		{
+			gl_RenderState.ApplyLightIndex(d);
+		}
+	}
+}
+
+//==========================================================================
+//
+//
+//
+//==========================================================================
+
+void FDrawInfo::SetupSectorLights(GLFlat *flat, int pass, int *dli)
+{
+	if (dli != NULL && *dli != -1)
+	{
+		gl_RenderState.ApplyLightIndex(GLRenderer->mLights->GetIndex(*dli));
+		(*dli)++;
+		return;
+	}
+	if (flat->SetupSectorLights(pass, flat->sector, lightdata))
 	{
 		int d = GLRenderer->mLights->UploadLights(lightdata);
 		if (pass == GLPASS_LIGHTSONLY)
@@ -137,15 +167,22 @@ void FDrawInfo::ProcessLights(GLFlat *flat, bool istrans)
 {
 	flat->dynlightindex = GLRenderer->mLights->GetIndexPtr();
 
+	if (flat->sector->ibocount > 0 && !gl_render_subsectors && !gl_RenderState.GetClipLineShouldBeActive())
+	{
+		SetupSectorLights(flat, GLPASS_LIGHTSONLY, nullptr);
+	}
+	else
+	{
 	// Draw the subsectors belonging to this sector
-	for (int i=0; i< flat->sector->subsectorcount; i++)
+		for (int i = 0; i < flat->sector->subsectorcount; i++)
 	{
 		subsector_t * sub = flat->sector->subsectors[i];
-		if (ss_renderflags[sub->Index()]& flat->renderflags || istrans)
+			if (ss_renderflags[sub->Index()] & flat->renderflags || istrans)
 		{
 			SetupSubsectorLights(flat, GLPASS_LIGHTSONLY, sub, nullptr);
 		}
 	}
+	}
 
 	// Draw the subsectors assigned to it due to missing textures
 	if (!(flat->renderflags&SSRF_RENDER3DPLANES))
@@ -175,29 +212,40 @@ void FDrawInfo::DrawSubsectors(GLFlat *flat, int pass, bool processlights, bool
 
 	gl_RenderState.Apply();
 	if (gl.legacyMode) processlights = false;
-	if (flat->vboindex >= 0)
+
+	auto vcount = flat->sector->ibocount;
+	if (vcount > 0 && !gl_render_subsectors && !gl_RenderState.GetClipLineShouldBeActive())
+	{
+		if (processlights) SetupSectorLights(flat, GLPASS_ALL, &dli);
+		drawcalls.Clock();
+		glDrawElements(GL_TRIANGLES, vcount, GL_UNSIGNED_INT, GLRenderer->mVBO->GetIndexPointer() + flat->vboindex);
+		drawcalls.Unclock();
+		flatvertices += vcount;
+		flatprimitives++;
+	}
+	else if (flat->vboindex >= 0)
 	{
 		int index = flat->vboindex;
 		for (int i=0; i<flat->sector->subsectorcount; i++)
 		{
 			subsector_t * sub = flat->sector->subsectors[i];
+			if (sub->numlines <= 2) continue;
 				
 			if (ss_renderflags[sub->Index()]& flat->renderflags || istrans)
 			{
 				if (processlights) SetupSubsectorLights(flat, GLPASS_ALL, sub, &dli);
 				drawcalls.Clock();
-				glDrawArrays(GL_TRIANGLE_FAN, index, sub->numlines);
+				glDrawElements(GL_TRIANGLES, (sub->numlines - 2) * 3, GL_UNSIGNED_INT, GLRenderer->mVBO->GetIndexPointer() + index);
 				drawcalls.Unclock();
 				flatvertices += sub->numlines;
 				flatprimitives++;
 			}
-			index += sub->numlines;
+			index += (sub->numlines - 2) * 3;
 		}
 	}
 	else
 	{
 		// Draw the subsectors belonging to this sector
-		// (can this case even happen?)
 		for (int i=0; i<flat->sector->subsectorcount; i++)
 		{
 			subsector_t * sub = flat->sector->subsectors[i];
diff --git a/src/hwrenderer/data/flatvertices.cpp b/src/hwrenderer/data/flatvertices.cpp
index f069a7989e..5771012bc4 100644
--- a/src/hwrenderer/data/flatvertices.cpp
+++ b/src/hwrenderer/data/flatvertices.cpp
@@ -118,13 +118,22 @@ static F3DFloor *Find3DFloor(sector_t *target, sector_t *model)
 //
 //==========================================================================
 
-int FFlatVertexGenerator::CreateSubsectorVertices(subsector_t *sub, const secplane_t &plane, int floor)
+int FFlatVertexGenerator::CreateIndexedSubsectorVertices(subsector_t *sub, const secplane_t &plane, int floor, int vi, FFlatVertexGenerator::FIndexGenerationInfo &gen)
 {
-	int idx = vbo_shadowdata.Reserve(sub->numlines);
-	for(unsigned int k=0; k<sub->numlines; k++, idx++)
+	if (sub->numlines < 3) return -1;
+
+	int idx = ibo_data.Reserve((sub->numlines - 2) * 3);
+	int idxc = idx;
+	int firstndx = gen.GetIndex(sub->firstline[0].v1);
+	int secondndx = gen.GetIndex(sub->firstline[1].v1);
+	for (unsigned int k = 2; k<sub->numlines; k++)
 	{
-		vbo_shadowdata[idx].SetFlatVertex(sub->firstline[k].v1, plane);
-		if (sub->sector->transdoor && floor) vbo_shadowdata[idx].z -= 1.f;
+		auto ndx = gen.GetIndex(sub->firstline[k].v1);
+
+		ibo_data[idx++] = vi + firstndx;
+		ibo_data[idx++] = vi + secondndx;
+		ibo_data[idx++] = vi + ndx;
+		secondndx = ndx;
 	}
 	return idx;
 }
@@ -135,15 +144,28 @@ int FFlatVertexGenerator::CreateSubsectorVertices(subsector_t *sub, const secpla
 //
 //==========================================================================
 
-int FFlatVertexGenerator::CreateSectorVertices(sector_t *sec, const secplane_t &plane, int floor)
+int FFlatVertexGenerator::CreateIndexedSectorVertices(sector_t *sec, const secplane_t &plane, int floor, FFlatVertexGenerator::FIndexGenerationInfo &gen)
 {
-	int rt = vbo_shadowdata.Size();
-	// First calculate the vertices for the sector itself
-	for(int j=0; j<sec->subsectorcount; j++)
+	int rt = ibo_data.Size();
+	int vi = vbo_shadowdata.Reserve(gen.vertices.Size());
+	float diff;
+
+	// Create the actual vertices.
+	if (sec->transdoor && floor) diff = -1.f;
+	else diff = 0.f;
+	for (unsigned i = 0; i < gen.vertices.Size(); i++)
+	{
+		vbo_shadowdata[vi + i].SetFlatVertex(gen.vertices[i], plane);
+		vbo_shadowdata[vi + i].z += diff;
+	}
+	
+	// Create the indices for the subsectors
+	for (int j = 0; j<sec->subsectorcount; j++)
 	{
 		subsector_t *sub = sec->subsectors[j];
-		CreateSubsectorVertices(sub, plane, floor);
+		CreateIndexedSubsectorVertices(sub, plane, floor, vi, gen);
 	}
+	sec->ibocount = ibo_data.Size() - rt;
 	return rt;
 }
 
@@ -153,23 +175,23 @@ int FFlatVertexGenerator::CreateSectorVertices(sector_t *sec, const secplane_t &
 //
 //==========================================================================
 
-int FFlatVertexGenerator::CreateVertices(int h, sector_t *sec, const secplane_t &plane, int floor)
+int FFlatVertexGenerator::CreateIndexedVertices(int h, sector_t *sec, const secplane_t &plane, int floor, TArray<FFlatVertexGenerator::FIndexGenerationInfo> &gen)
 {
 	// First calculate the vertices for the sector itself
 	sec->vboheight[h] = sec->GetPlaneTexZ(h);
-	sec->vboindex[h] = CreateSectorVertices(sec, plane, floor);
+	sec->vboindex[h] = CreateIndexedSectorVertices(sec, plane, floor, gen[sec->Index()]);
 
 	// Next are all sectors using this one as heightsec
 	TArray<sector_t *> &fakes = sec->e->FakeFloor.Sectors;
-	for (unsigned g=0; g<fakes.Size(); g++)
+	for (unsigned g = 0; g<fakes.Size(); g++)
 	{
 		sector_t *fsec = fakes[g];
-		fsec->vboindex[2+h] = CreateSectorVertices(fsec, plane, false);
+		fsec->vboindex[2 + h] = CreateIndexedSectorVertices(fsec, plane, false, gen[fsec->Index()]);
 	}
 
 	// and finally all attached 3D floors
 	TArray<sector_t *> &xf = sec->e->XFloor.attached;
-	for (unsigned g=0; g<xf.Size(); g++)
+	for (unsigned g = 0; g<xf.Size(); g++)
 	{
 		sector_t *fsec = xf[g];
 		F3DFloor *ffloor = Find3DFloor(fsec, sec);
@@ -181,10 +203,9 @@ int FFlatVertexGenerator::CreateVertices(int h, sector_t *sec, const secplane_t
 
 			if (dotop || dobottom)
 			{
-				if (dotop) ffloor->top.vindex = vbo_shadowdata.Size();
-				if (dobottom) ffloor->bottom.vindex = vbo_shadowdata.Size();
-	
-				CreateSectorVertices(fsec, plane, false);
+				auto ndx = CreateIndexedSectorVertices(fsec, plane, false, gen[fsec->Index()]);
+				if (dotop) ffloor->top.vindex = ndx;
+				if (dobottom) ffloor->bottom.vindex = ndx;
 			}
 		}
 	}
@@ -199,13 +220,28 @@ int FFlatVertexGenerator::CreateVertices(int h, sector_t *sec, const secplane_t
 //
 //==========================================================================
 
-void FFlatVertexGenerator::CreateFlatVertices()
+void FFlatVertexGenerator::CreateIndexedFlatVertices()
 {
+	TArray<FIndexGenerationInfo> gen;
+	gen.Resize(level.sectors.Size());
+	// This must be generated up front so that the following code knows how many vertices a sector contains.
+	for (unsigned i = 0; i < level.sectors.Size(); i++)
+	{
+		for (int j = 0; j < level.sectors[i].subsectorcount; j++)
+		{
+			auto sub = level.sectors[i].subsectors[j];
+			for (unsigned k = 0; k < sub->numlines; k++)
+			{
+				auto vert = sub->firstline[k].v1;
+				gen[i].AddVertex(vert);
+			}
+		}
+	}
 	for (int h = sector_t::floor; h <= sector_t::ceiling; h++)
 	{
-		for(auto &sec : level.sectors)
+		for (auto &sec : level.sectors)
 		{
-			CreateVertices(h, &sec, sec.GetSecPlane(h), h == sector_t::floor);
+			CreateIndexedVertices(h, &sec, sec.GetSecPlane(h), h == sector_t::floor, gen);
 		}
 	}
 
@@ -213,7 +249,7 @@ void FFlatVertexGenerator::CreateFlatVertices()
 	// No new vertices are needed here. The planes come from the actual sector
 	for (auto &sec : level.sectors)
 	{
-		for(auto ff : sec.e->XFloor.ffloors)
+		for (auto ff : sec.e->XFloor.ffloors)
 		{
 			if (ff->top.model == &sec)
 			{
@@ -257,7 +293,7 @@ void FFlatVertexGenerator::UpdatePlaneVertices(sector_t *sec, int plane)
 void FFlatVertexGenerator::CreateVertices()
 {
 	vbo_shadowdata.Resize(NUM_RESERVED);
-	CreateFlatVertices();
+	CreateIndexedFlatVertices();
 }
 
 //==========================================================================
diff --git a/src/hwrenderer/data/flatvertices.h b/src/hwrenderer/data/flatvertices.h
index ee390218f8..3025a6820d 100644
--- a/src/hwrenderer/data/flatvertices.h
+++ b/src/hwrenderer/data/flatvertices.h
@@ -45,8 +45,32 @@ class FFlatVertexGenerator
 {
 protected:
 	TArray<FFlatVertex> vbo_shadowdata;
+	TArray<uint32_t> ibo_data;
 	FFlatVertex *mMap;
 
+	// Temporary data for creating an indexed buffer
+	struct FIndexGenerationInfo
+	{
+		TArray<vertex_t *> vertices;
+		TMap<vertex_t*, uint32_t> vertexmap;
+
+		uint32_t AddVertex(vertex_t *vert)
+		{
+			auto check = vertexmap.CheckKey(vert);
+			if (check != nullptr) return *check;
+			auto index = vertices.Push(vert);
+			vertexmap[vert] = index;
+			return index;
+		}
+
+		uint32_t GetIndex(vertex_t *vert)
+		{
+			auto check = vertexmap.CheckKey(vert);
+			if (check != nullptr) return *check;
+			return ~0;
+		}
+	};
+
 
 public:
 	enum
@@ -65,10 +89,11 @@ public:
 	void OutputResized(int width, int height);
 
 private:
-	int CreateSubsectorVertices(subsector_t *sub, const secplane_t &plane, int floor);
-	int CreateSectorVertices(sector_t *sec, const secplane_t &plane, int floor);
-	int CreateVertices(int h, sector_t *sec, const secplane_t &plane, int floor);
-	void CreateFlatVertices();
+	int CreateIndexedSubsectorVertices(subsector_t *sub, const secplane_t &plane, int floor, int vi, FIndexGenerationInfo &gen);
+	int CreateIndexedSectorVertices(sector_t *sec, const secplane_t &plane, int floor, FIndexGenerationInfo &gen);
+	int CreateIndexedVertices(int h, sector_t *sec, const secplane_t &plane, int floor, TArray<FIndexGenerationInfo> &gen);
+	void CreateIndexedFlatVertices();
+
 	void UpdatePlaneVertices(sector_t *sec, int plane);
 protected:
 	void CreateVertices();
diff --git a/src/hwrenderer/scene/hw_drawstructs.h b/src/hwrenderer/scene/hw_drawstructs.h
index 7aa7e0b7df..56c74a8f79 100644
--- a/src/hwrenderer/scene/hw_drawstructs.h
+++ b/src/hwrenderer/scene/hw_drawstructs.h
@@ -311,7 +311,9 @@ public:
 
 	int dynlightindex;
 
+	bool SetupLights(int pass, FLightNode *head, FDynLightData &lightdata, int portalgroup);
 	bool SetupSubsectorLights(int pass, subsector_t * sub, FDynLightData &lightdata);
+	bool SetupSectorLights(int pass, sector_t * sec, FDynLightData &lightdata);
 
 	void PutFlat(HWDrawInfo *di, bool fog = false);
 	void Process(HWDrawInfo *di, sector_t * model, int whichplane, bool notexture);
diff --git a/src/hwrenderer/scene/hw_flats.cpp b/src/hwrenderer/scene/hw_flats.cpp
index dabee535d6..fa1ff287a7 100644
--- a/src/hwrenderer/scene/hw_flats.cpp
+++ b/src/hwrenderer/scene/hw_flats.cpp
@@ -92,14 +92,13 @@ bool hw_SetPlaneTextureRotation(const GLSectorPlane * secplane, FMaterial * glte
 //
 //==========================================================================
 
-bool GLFlat::SetupSubsectorLights(int pass, subsector_t * sub, FDynLightData &lightdata)
+bool GLFlat::SetupLights(int pass, FLightNode * node, FDynLightData &lightdata, int portalgroup)
 {
 	Plane p;
 
 	if (renderstyle == STYLE_Add && !level.lightadditivesurfaces) return false;	// no lights on additively blended surfaces.
 
 	lightdata.Clear();
-	FLightNode * node = sub->lighthead;
 	while (node)
 	{
 		ADynamicLight * light = node->lightsource;
@@ -121,13 +120,23 @@ bool GLFlat::SetupSubsectorLights(int pass, subsector_t * sub, FDynLightData &li
 		}
 
 		p.Set(plane.plane.Normal(), plane.plane.fD());
-		lightdata.GetLight(sub->sector->PortalGroup, p, light, false);
+		lightdata.GetLight(portalgroup, p, light, false);
 		node = node->nextLight;
 	}
 
 	return true;
 }
 
+bool GLFlat::SetupSubsectorLights(int pass, subsector_t * sub, FDynLightData &lightdata)
+{
+	return SetupLights(pass, sub->lighthead, lightdata, sub->sector->PortalGroup);
+}
+
+bool GLFlat::SetupSectorLights(int pass, sector_t * sec, FDynLightData &lightdata)
+{
+	return SetupLights(pass, sec->lighthead, lightdata, sec->PortalGroup);
+}
+
 //==========================================================================
 //
 // GLFlat::PutFlat
diff --git a/src/hwrenderer/scene/hw_renderhacks.cpp b/src/hwrenderer/scene/hw_renderhacks.cpp
index d92951aa9a..57fef57e00 100644
--- a/src/hwrenderer/scene/hw_renderhacks.cpp
+++ b/src/hwrenderer/scene/hw_renderhacks.cpp
@@ -1090,6 +1090,7 @@ void HWDrawInfo::ProcessSectorStacks(area_t in_area)
 				{				
 					subsector_t *sub = HandledSubsectors[j];
 					ss_renderflags[sub->Index()] &= ~SSRF_RENDERCEILING;
+					sub->sector->ibocount = -1;	// cannot render this sector in one go.
 
 					if (sub->portalcoverage[sector_t::ceiling].subsectors == NULL)
 					{
@@ -1135,6 +1136,7 @@ void HWDrawInfo::ProcessSectorStacks(area_t in_area)
 				{				
 					subsector_t *sub = HandledSubsectors[j];
 					ss_renderflags[sub->Index()] &= ~SSRF_RENDERFLOOR;
+					sub->sector->ibocount = -1;	// cannot render this sector in one go.
 
 					if (sub->portalcoverage[sector_t::floor].subsectors == NULL)
 					{
diff --git a/src/p_3dfloors.cpp b/src/p_3dfloors.cpp
index 4254c92d49..5c6096f842 100644
--- a/src/p_3dfloors.cpp
+++ b/src/p_3dfloors.cpp
@@ -120,6 +120,7 @@ static void P_Add3DFloor(sector_t* sec, sector_t* sec2, line_t* master, int flag
 	ffloor->top.copied = ffloor->bottom.copied = false;
 	ffloor->top.model = ffloor->bottom.model = ffloor->model = sec2;
 	ffloor->target = sec;
+	ffloor->top.vindex = ffloor->bottom.vindex = -1;
 
 	if (!(flags&FF_THINFLOOR))
 	{
diff --git a/src/p_setup.cpp b/src/p_setup.cpp
index 56850f6a01..dba5a109e3 100644
--- a/src/p_setup.cpp
+++ b/src/p_setup.cpp
@@ -1510,6 +1510,7 @@ void P_LoadSectors (MapData *map, FMissingTextureTracker &missingtex)
 		ss->friction = ORIG_FRICTION;
 		ss->movefactor = ORIG_FRICTION_FACTOR;
 		ss->sectornum = i;
+		ss->ibocount = -1;
 	}
 	delete[] msp;
 }
diff --git a/src/p_udmf.cpp b/src/p_udmf.cpp
index 283fac0004..6acf9e37c5 100644
--- a/src/p_udmf.cpp
+++ b/src/p_udmf.cpp
@@ -1383,6 +1383,7 @@ public:
 		sec->sectornum = index;
 		sec->damageinterval = 32;
 		sec->terrainnum[sector_t::ceiling] = sec->terrainnum[sector_t::floor] = -1;
+		sec->ibocount = -1;
 		memset(sec->SpecialColors, -1, sizeof(sec->SpecialColors));
 		if (floordrop) sec->Flags = SECF_FLOORDROP;
 		// killough 3/7/98: end changes
diff --git a/src/r_defs.h b/src/r_defs.h
index d5b104624d..17fcc5cad0 100644
--- a/src/r_defs.h
+++ b/src/r_defs.h
@@ -1087,9 +1087,10 @@ public:
 		vbo_fakeceiling = ceiling+2,
 	};
 
-	int				vboindex[4];	// VBO indices of the 4 planes this sector uses during rendering
+	int				vboindex[4];	// VBO/IBO indices of the 4 planes this sector uses during rendering
 	double			vboheight[2];	// Last calculated height for the 2 planes of this actual sector
-	int				vbocount[2];	// Total count of vertices belonging to this sector's planes
+	int				vbocount[2];	// Total count of vertices belonging to this sector's planes. This is used when a sector height changes and also contains all attached planes.
+	int				ibocount;		// number of indices per plane (identical for all planes.) If this is -1 the index buffer is not in use.
 
 	float GetReflect(int pos) { return gl_plane_reflection_i? reflect[pos] : 0; }
 	bool VBOHeightcheck(int pos) const { return vboheight[pos] == GetPlaneTexZ(pos); }
diff --git a/src/win32/win32gliface.cpp b/src/win32/win32gliface.cpp
index bd4600bb0f..cb6da5ff9b 100644
--- a/src/win32/win32gliface.cpp
+++ b/src/win32/win32gliface.cpp
@@ -1159,10 +1159,15 @@ bool SystemFrameBuffer::IsFullscreen()
 // 
 //
 //==========================================================================
+EXTERN_CVAR(Bool, vid_vsync);
+CUSTOM_CVAR(Bool, gl_control_tear, true, CVAR_ARCHIVE | CVAR_GLOBALCONFIG)
+{
+	vid_vsync.Callback();
+}
 
 void SystemFrameBuffer::SetVSync (bool vsync)
 {
-	if (myWglSwapIntervalExtProc != NULL) myWglSwapIntervalExtProc(vsync ? SwapInterval : 0);
+	if (myWglSwapIntervalExtProc != NULL) myWglSwapIntervalExtProc(vsync ? (gl_control_tear? SwapInterval : 1) : 0);
 }
 
 void SystemFrameBuffer::SwapBuffers()
diff --git a/wadsrc/static/shaders/glsl/material_normal.fp b/wadsrc/static/shaders/glsl/material_normal.fp
index b048f45597..6b65de6a3b 100644
--- a/wadsrc/static/shaders/glsl/material_normal.fp
+++ b/wadsrc/static/shaders/glsl/material_normal.fp
@@ -9,6 +9,10 @@ vec3 lightContribution(int i, vec3 normal)
 	float lightdistance = distance(lightpos.xyz, pixelpos.xyz);
 	if (lightpos.w < lightdistance)
 		return vec3(0.0); // Early out lights touching surface but not this fragment
+
+	vec3 lightdir = normalize(lightpos.xyz - pixelpos.xyz);
+	float dotprod = dot(normal, lightdir);
+	if (dotprod < 0.0) return vec3(0.0);	// light hits from the backside. This can happen with full sector light lists and must be rejected for all cases.
 	
 	float attenuation = clamp((lightpos.w - lightdistance) / lightpos.w, 0.0, 1.0);
 
@@ -17,8 +21,7 @@ vec3 lightContribution(int i, vec3 normal)
 
 	if (lightcolor.a < 0.0) // Sign bit is the attenuated light flag
 	{
-		vec3 lightdir = normalize(lightpos.xyz - pixelpos.xyz);
-		attenuation *= clamp(dot(normal, lightdir), 0.0, 1.0);
+		attenuation *= clamp(dotprod, 0.0, 1.0);
 	}
 
 	if (attenuation > 0.0) // Skip shadow map test if possible
diff --git a/wadsrc/static/zscript/statusbar/sbarinfowrapper.txt b/wadsrc/static/zscript/statusbar/sbarinfowrapper.txt
index efc6bedc8b..96f0063208 100644
--- a/wadsrc/static/zscript/statusbar/sbarinfowrapper.txt
+++ b/wadsrc/static/zscript/statusbar/sbarinfowrapper.txt
@@ -12,7 +12,7 @@ struct SBarInfo native ui
 }
 
 
-// The sole purpose of this wrapper is to elimintate the native dependencies of the status bar object
+// The sole purpose of this wrapper is to eliminate the native dependencies of the status bar object
 // because those would seriously impede the script conversion of the base class.
 
 class SBarInfoWrapper : BaseStatusBar