diff --git a/src/g_shared/a_dynlight.cpp b/src/g_shared/a_dynlight.cpp
index b6e83abdc..e8dc871bf 100644
--- a/src/g_shared/a_dynlight.cpp
+++ b/src/g_shared/a_dynlight.cpp
@@ -80,7 +80,7 @@ DEFINE_CLASS_PROPERTY(type, S, DynamicLight)
 {
 	PROP_STRING_PARM(str, 0);
 	static const char * ltype_names[]={
-		"Point","Pulse","Flicker","Sector","RandomFlicker", "ColorPulse", "ColorFlicker", "RandomColorFlicker", NULL};
+		"Point","Pulse","Flicker","Sector","RandomFlicker", "ColorPulse", "ColorFlicker", "RandomColorFlicker", nullptr};
 
 	static const int ltype_values[]={
 		PointLight, PulseLight, FlickerLight, SectorLight, RandomFlickerLight, ColorPulseLight, ColorFlickerLight, RandomColorFlickerLight };
@@ -182,7 +182,7 @@ void ADynamicLight::PostBeginPlay()
 	
 	if (!(SpawnFlags & MTF_DORMANT))
 	{
-		Activate (NULL);
+		Activate (nullptr);
 	}
 
 	subsector = R_PointInSubsector(Pos());
@@ -430,14 +430,14 @@ void ADynamicLight::SetOffset(const DVector3 &pos)
 //==========================================================================
 //
 // The target pointer in dynamic lights should never be substituted unless 
-// notOld is NULL (which indicates that the object was destroyed by force.)
+// notOld is nullptr (which indicates that the object was destroyed by force.)
 //
 //==========================================================================
 size_t ADynamicLight::PointerSubstitution (DObject *old, DObject *notOld)
 {
 	AActor *saved_target = target;
 	size_t ret = Super::PointerSubstitution(old, notOld);
-	if (notOld != NULL) target = saved_target;
+	if (notOld != nullptr) target = saved_target;
 	return ret;
 }
 
@@ -494,7 +494,7 @@ FLightNode * AddLightNode(FLightNode ** thread, void * linkto, ADynamicLight * l
 //
 // P_DelSecnode() deletes a sector node from the list of
 // sectors this object appears in. Returns a pointer to the next node
-// on the linked list, or NULL.
+// on the linked list, or nullptr.
 //
 //=============================================================================
 
@@ -516,7 +516,7 @@ static FLightNode * DeleteLightNode(FLightNode * node)
 		delete node;
 		return(tn);
     }
-	return(NULL);
+	return(nullptr);
 }                             // phares 3/13/98
 
 
@@ -527,20 +527,20 @@ static FLightNode * DeleteLightNode(FLightNode * node)
 //
 //==========================================================================
 
-double ADynamicLight::DistToSeg(const DVector3 &pos, seg_t *seg)
+double ADynamicLight::DistToSeg(const DVector3 &pos, FSectionLine *segment)
 {
 	double u, px, py;
 
-	double seg_dx = seg->v2->fX() - seg->v1->fX();
-	double seg_dy = seg->v2->fY() - seg->v1->fY();
+	double seg_dx = segment->end->fX() - segment->start->fX();
+	double seg_dy = segment->end->fY() - segment->start->fY();
 	double seg_length_sq = seg_dx * seg_dx + seg_dy * seg_dy;
 
-	u = (((pos.X - seg->v1->fX()) * seg_dx) + (pos.Y - seg->v1->fY()) * seg_dy) / seg_length_sq;
+	u = (((pos.X - segment->start->fX()) * seg_dx) + (pos.Y - segment->start->fY()) * seg_dy) / seg_length_sq;
 	if (u < 0.) u = 0.; // clamp the test point to the line segment
 	else if (u > 1.) u = 1.;
 
-	px = seg->v1->fX() + (u * seg_dx);
-	py = seg->v1->fY() + (u * seg_dy);
+	px = segment->start->fX() + (u * seg_dx);
+	py = segment->start->fY() + (u * seg_dy);
 
 	px -= pos.X;
 	py -= pos.Y;
@@ -557,108 +557,110 @@ double ADynamicLight::DistToSeg(const DVector3 &pos, seg_t *seg)
 //==========================================================================
 struct LightLinkEntry
 {
-	subsector_t *sub;
+	FSection *sect;
 	DVector3 pos;
 };
 static TArray<LightLinkEntry> collected_ss;
 
-void ADynamicLight::CollectWithinRadius(const DVector3 &opos, subsector_t *subSec, float radius)
+void ADynamicLight::CollectWithinRadius(const DVector3 &opos, FSection *section, float radius)
 {
-	if (!subSec) return;
+	if (!section) return;
 	collected_ss.Clear();
-	collected_ss.Push({ subSec, opos });
-	subSec->validcount = ::validcount;
+	collected_ss.Push({ section, opos });
+	section->validcount = dl_validcount;
 
 	bool hitonesidedback = false;
 	for (unsigned i = 0; i < collected_ss.Size(); i++)
 	{
-		subSec = collected_ss[i].sub;
+		section = collected_ss[i].sect;
 
-		//touching_subsectors = AddLightNode(&subSec->lighthead, subSec, this, touching_subsectors);
-		if (subSec->sector->validcount != ::validcount)
-		{
-			touching_sector = AddLightNode(&subSec->render_sector->lighthead, subSec->sector, this, touching_sector);
-			subSec->sector->validcount = ::validcount;
-		}
+		touching_sector = AddLightNode(&section->lighthead, section, this, touching_sector);
 
-		for (unsigned int j = 0; j < subSec->numlines; ++j)
+		for (auto &segment : section->segments)
 		{
 			auto &pos = collected_ss[i].pos;
-			seg_t *seg = subSec->firstline + j;
 
 			// check distance from x/y to seg and if within radius add this seg and, if present the opposing subsector (lather/rinse/repeat)
 			// If out of range we do not need to bother with this seg.
-			if (DistToSeg(pos, seg) <= radius)
+			if (DistToSeg(pos, &segment) <= radius)
 			{
-				if (seg->sidedef && seg->linedef && seg->linedef->validcount != ::validcount)
+				if (segment.sidedef)
 				{
-					// light is in front of the seg
-					if ((pos.Y - seg->v1->fY()) * (seg->v2->fX() - seg->v1->fX()) + (seg->v1->fX() - pos.X) * (seg->v2->fY() - seg->v1->fY()) <= 0)
+					auto sidedef = segment.sidedef;
+					auto linedef = sidedef->linedef;
+					if (linedef && linedef->validcount != ::validcount)
 					{
-						seg->linedef->validcount = validcount;
-						touching_sides = AddLightNode(&seg->sidedef->lighthead, seg->sidedef, this, touching_sides);
-					}
-					else if (seg->linedef->sidedef[0] == seg->sidedef && seg->linedef->sidedef[1] == nullptr)
-					{
-						hitonesidedback = true;
-					}
-				}
-				if (seg->linedef)
-				{
-					FLinePortal *port = seg->linedef->getPortal();
-					if (port && port->mType == PORTT_LINKED)
-					{
-						line_t *other = port->mDestination;
-						if (other->validcount != ::validcount)
+						// light is in front of the seg
+						if ((pos.Y - segment.start->fY()) * (segment.end->fX() - segment.start->fX()) + (segment.start->fX() - pos.X) * (segment.end->fY() - segment.start->fY()) <= 0)
 						{
-							subsector_t *othersub = R_PointInSubsector(other->v1->fPos() + other->Delta() / 2);
-							if (othersub->validcount != ::validcount)
+							linedef->validcount = ::validcount;
+							touching_sides = AddLightNode(&sidedef->lighthead, sidedef, this, touching_sides);
+						}
+						else if (linedef->sidedef[0] == sidedef && linedef->sidedef[1] == nullptr)
+						{
+							hitonesidedback = true;
+						}
+					}
+					if (linedef)
+					{
+						FLinePortal *port = linedef->getPortal();
+						if (port && port->mType == PORTT_LINKED)
+						{
+							line_t *other = port->mDestination;
+							if (other->validcount != ::validcount)
 							{
-								othersub->validcount = ::validcount;
-								collected_ss.Push({ othersub, PosRelative(other) });
+								subsector_t *othersub = R_PointInSubsector(other->v1->fPos() + other->Delta() / 2);
+								FSection *othersect = othersub->section;
+								if (othersect->validcount != ::validcount)
+								{
+									othersect->validcount = ::validcount;
+									collected_ss.Push({ othersect, PosRelative(other) });
+								}
 							}
 						}
 					}
 				}
 
-				seg_t *partner = seg->PartnerSeg;
+				auto partner = segment.partner;
 				if (partner)
 				{
-					subsector_t *sub = partner->Subsector;
-					if (sub != NULL && sub->validcount != ::validcount)
+					FSection *sect = partner->section;
+					if (sect != nullptr && sect->validcount != dl_validcount)
 					{
-						sub->validcount = ::validcount;
-						collected_ss.Push({ sub, pos });
+						sect->validcount = dl_validcount;
+						collected_ss.Push({ sect, pos });
 					}
 				}
 			}
 		}
-		sector_t *sec = subSec->sector;
+		sector_t *sec = section->sector;
 		if (!sec->PortalBlocksSight(sector_t::ceiling))
 		{
-			line_t *other = subSec->firstline->linedef;
+			line_t *other = section->segments[0].sidedef->linedef;
 			if (sec->GetPortalPlaneZ(sector_t::ceiling) < Z() + radius)
 			{
 				DVector2 refpos = other->v1->fPos() + other->Delta() / 2 + sec->GetPortalDisplacement(sector_t::ceiling);
 				subsector_t *othersub = R_PointInSubsector(refpos);
-				if (othersub->validcount != ::validcount)
+				FSection *othersect = othersub->section;
+				if (othersect->validcount != dl_validcount)
 				{
-					othersub->validcount = ::validcount;
-					collected_ss.Push({ othersub, PosRelative(othersub->sector) });
+					othersect->validcount = dl_validcount;
+					collected_ss.Push({ othersect, PosRelative(othersub->sector) });
 				}
 			}
 		}
 		if (!sec->PortalBlocksSight(sector_t::floor))
 		{
-			line_t *other = subSec->firstline->linedef;
+			line_t *other = section->segments[0].sidedef->linedef;
 			if (sec->GetPortalPlaneZ(sector_t::floor) > Z() - radius)
 			{
 				DVector2 refpos = other->v1->fPos() + other->Delta() / 2 + sec->GetPortalDisplacement(sector_t::floor);
 				subsector_t *othersub = R_PointInSubsector(refpos);
-				if (othersub->validcount != ::validcount)
+				FSection *othersect = othersub->section;
+				if (othersect->validcount != dl_validcount)
 				{
-					othersub->validcount = ::validcount;
-					collected_ss.Push({ othersub, PosRelative(othersub->sector) });
+					othersect->validcount = dl_validcount;
+					collected_ss.Push({ othersect, PosRelative(othersub->sector) });
 				}
 			}
 		}
@@ -680,32 +682,33 @@ void ADynamicLight::LinkLight()
 	node = touching_sides;
 	while (node)
     {
-		node->lightsource = NULL;
+		node->lightsource = nullptr;
 		node = node->nextTarget;
     }
 	node = touching_sector;
 	while (node)
 	{
-		node->lightsource = NULL;
+		node->lightsource = nullptr;
 		node = node->nextTarget;
 	}
 
 	if (radius>0)
 	{
 		// passing in radius*radius allows us to do a distance check without any calls to sqrt
-		subsector_t * subSec = R_PointInSubsector(Pos());
-		::validcount++;
-		CollectWithinRadius(Pos(), subSec, float(radius*radius));
+		FSection *sect = R_PointInSubsector(Pos())->section;
+
+		dl_validcount++;
+		CollectWithinRadius(Pos(), sect, float(radius*radius));
 
 	}
 		
 	// Now delete any nodes that won't be used. These are the ones where
-	// m_thing is still NULL.
+	// m_thing is still nullptr.
 	
 	node = touching_sides;
 	while (node)
 	{
-		if (node->lightsource == NULL)
+		if (node->lightsource == nullptr)
 		{
 			node = DeleteLightNode(node);
 		}
@@ -716,7 +719,7 @@ void ADynamicLight::LinkLight()
 	node = touching_sector;
 	while (node)
 	{
-		if (node->lightsource == NULL)
+		if (node->lightsource == nullptr)
 		{
 			node = DeleteLightNode(node);
 		}
@@ -733,7 +736,7 @@ void ADynamicLight::LinkLight()
 //==========================================================================
 void ADynamicLight::UnlinkLight ()
 {
-	if (owned && target != NULL)
+	if (owned && target != nullptr)
 	{
 		// Delete reference in owning actor
 		for(int c=target->AttachedLights.Size()-1; c>=0; c--)
@@ -770,7 +773,7 @@ void AActor::AttachLight(unsigned int count, const FLightDefaults *lightdef)
 	if (count < AttachedLights.Size()) 
 	{
 		light = barrier_cast<ADynamicLight*>(AttachedLights[count]);
-		assert(light != NULL);
+		assert(light != nullptr);
 	}
 	else
 	{
@@ -797,13 +800,13 @@ void AActor::SetDynamicLights()
 	TArray<FInternalLightAssociation *> & LightAssociations = GetInfo()->LightAssociations;
 	unsigned int count = 0;
 
-	if (state == NULL) return;
+	if (state == nullptr) return;
 	if (LightAssociations.Size() > 0)
 	{
 		ADynamicLight *lights, *tmpLight;
 		unsigned int i;
 
-		lights = tmpLight = NULL;
+		lights = tmpLight = nullptr;
 
 		for (i = 0; i < LightAssociations.Size(); i++)
 		{
@@ -816,7 +819,7 @@ void AActor::SetDynamicLights()
 	}
 	if (count == 0 && state->Light > 0)
 	{
-		for(int i= state->Light; StateLights[i] != NULL; i++)
+		for(int i= state->Light; StateLights[i] != nullptr; i++)
 		{
 			if (StateLights[i] != (FLightDefaults*)-1)
 			{
diff --git a/src/g_shared/a_dynlight.h b/src/g_shared/a_dynlight.h
index 671c7812f..d28b787b1 100644
--- a/src/g_shared/a_dynlight.h
+++ b/src/g_shared/a_dynlight.h
@@ -12,6 +12,7 @@ struct seg_t;
 
 class ADynamicLight;
 class FSerializer;
+struct FSectionLine;
 
 enum ELightType
 {
@@ -209,8 +210,8 @@ public:
 	FLightNode * touching_sector;
 
 private:
-	double DistToSeg(const DVector3 &pos, seg_t *seg);
-	void CollectWithinRadius(const DVector3 &pos, subsector_t *subSec, float radius);
+	double DistToSeg(const DVector3 &pos, FSectionLine *seg);
+	void CollectWithinRadius(const DVector3 &pos, FSection *section, float radius);
 
 protected:
 	DVector3 m_off;
diff --git a/src/hwrenderer/data/hw_sections.cpp b/src/hwrenderer/data/hw_sections.cpp
index 4ad20d47a..c43a22eeb 100644
--- a/src/hwrenderer/data/hw_sections.cpp
+++ b/src/hwrenderer/data/hw_sections.cpp
@@ -633,11 +633,9 @@ public:
 	{
 		output.allSections.Resize(groups.Size());
 		output.allIndices.Resize(level.subsectors.Size() + level.sides.Size() + 2*level.sectors.Size());
-		output.sectionForSubsectorPtr = &output.allIndices[0];
-		output.sectionForSidedefPtr = &output.allIndices[level.subsectors.Size()];
-		output.firstSectionForSectorPtr = &output.allIndices[level.subsectors.Size() + level.sides.Size()];
-		output.numberOfSectionForSectorPtr = &output.allIndices[level.subsectors.Size() + level.sides.Size() + level.sectors.Size()];
-		memset(output.sectionForSubsectorPtr, -1, sizeof(int) * level.subsectors.Size());
+		output.sectionForSidedefPtr = &output.allIndices[0];
+		output.firstSectionForSectorPtr = &output.allIndices[level.sides.Size()];
+		output.numberOfSectionForSectorPtr = &output.allIndices[level.sides.Size() + level.sectors.Size()];
 		memset(output.firstSectionForSectorPtr, -1, sizeof(int) * level.sectors.Size());
 		memset(output.numberOfSectionForSectorPtr, 0, sizeof(int) * level.sectors.Size());
 
@@ -704,6 +702,7 @@ public:
 				fseg.end = segment->end;
 				fseg.partner = segment->partner == nullptr ? nullptr : &output.allLines[segment->partner->tempindex];
 				fseg.sidedef = segment->sidedef;
+				fseg.section = &dest;
 				dest.bounds.addVertex(fseg.start->fX(), fseg.start->fY());
 				dest.bounds.addVertex(fseg.end->fX(), fseg.end->fY());
 			}
@@ -717,7 +716,7 @@ public:
 			for (auto ssi : group.subsectors)
 			{
 				output.allSubsectors[numsubsectors++] = &level.subsectors[ssi];
-				output.sectionForSubsectorPtr[ssi] = curgroup;
+				level.subsectors[ssi].section = &output.allSections[curgroup];
 			}
 			curgroup++;
 		}
diff --git a/src/hwrenderer/data/hw_sections.h b/src/hwrenderer/data/hw_sections.h
index 178d0ed84..668c2ba39 100644
--- a/src/hwrenderer/data/hw_sections.h
+++ b/src/hwrenderer/data/hw_sections.h
@@ -73,6 +73,7 @@ struct FSectionLine
 	vertex_t *start;
 	vertex_t *end;
 	FSectionLine *partner;
+	FSection *section;
 	side_t *sidedef;
 };
 
@@ -101,27 +102,10 @@ public:
 	TArray<subsector_t *> allSubsectors;
 	TArray<int> allIndices;
 
-	int *sectionForSubsectorPtr;			// stored inside allIndices
 	int *sectionForSidedefPtr;				// also stored inside allIndices;
 	int *firstSectionForSectorPtr;			// ditto.
 	int *numberOfSectionForSectorPtr;		// ditto.
 
-	FSection *SectionForSubsector(subsector_t *sub)
-	{
-		return SectionForSubsector(sub->Index());
-	}
-	FSection *SectionForSubsector(int ssindex)
-	{
-		return ssindex < 0 ? nullptr : &allSections[sectionForSubsectorPtr[ssindex]];
-	}
-	int SectionNumForSubsector(subsector_t *sub)
-	{
-		return SectionNumForSubsector(sub->Index());
-	}
-	int SectionNumForSubsector(int ssindex)
-	{
-		return ssindex < 0 ? -1 : sectionForSubsectorPtr[ssindex];
-	}
 	FSection *SectionForSidedef(side_t *side)
 	{
 		return SectionForSidedef(side->Index());
diff --git a/src/hwrenderer/scene/hw_bsp.cpp b/src/hwrenderer/scene/hw_bsp.cpp
index 92b911781..affca42a8 100644
--- a/src/hwrenderer/scene/hw_bsp.cpp
+++ b/src/hwrenderer/scene/hw_bsp.cpp
@@ -155,7 +155,7 @@ void HWDrawInfo::WorkerThread()
 		{
 			GLFlat flat;
 			SetupFlat.Clock();
-			flat.section = level.sections.SectionForSubsector(job->sub);
+			flat.section = job->sub->section;
 			front = hw_FakeFlat(job->sub->render_sector, &fakefront, in_area, false);
 			flat.ProcessSector(this, front);
 			SetupFlat.Unclock();
@@ -680,8 +680,7 @@ void HWDrawInfo::DoSubsector(subsector_t * sub)
 					fakesector = hw_FakeFlat(sector, &fake, in_area, false);
 				}
 
-				auto secnum = level.sections.SectionNumForSubsector(sub);
-				uint8_t &srf = section_renderflags[secnum];
+				uint8_t &srf = section_renderflags[level.sections.SectionIndex(sub->section)];
 				if (!(srf & SSRF_PROCESSED))
 				{
 					srf |= SSRF_PROCESSED;
@@ -693,7 +692,7 @@ void HWDrawInfo::DoSubsector(subsector_t * sub)
 					else
 					{
 						GLFlat flat;
-						flat.section = level.sections.SectionForSubsector(sub);
+						flat.section = sub->section;
 						SetupFlat.Clock();
 						flat.ProcessSector(this, fakesector);
 						SetupFlat.Unclock();
diff --git a/src/hwrenderer/scene/hw_flats.cpp b/src/hwrenderer/scene/hw_flats.cpp
index 2278bbd58..f7948e080 100644
--- a/src/hwrenderer/scene/hw_flats.cpp
+++ b/src/hwrenderer/scene/hw_flats.cpp
@@ -184,7 +184,7 @@ void GLFlat::DrawSubsectors(HWDrawInfo *di, FRenderState &state)
 {
 	if (level.HasDynamicLights && screen->BuffersArePersistent())
 	{
-		SetupLights(di, sector->lighthead, lightdata, sector->PortalGroup);
+		SetupLights(di, section->lighthead, lightdata, sector->PortalGroup);
 	}
 	state.SetLightIndex(dynlightindex);
 
@@ -346,7 +346,7 @@ inline void GLFlat::PutFlat(HWDrawInfo *di, bool fog)
 	{
 		if (level.HasDynamicLights && gltexture != nullptr)
 		{
-			SetupLights(di, sector->lighthead, lightdata, sector->PortalGroup);
+			SetupLights(di, section->lighthead, lightdata, sector->PortalGroup);
 		}
 	}
 	di->AddFlat(this, fog);
diff --git a/src/hwrenderer/scene/hw_renderhacks.cpp b/src/hwrenderer/scene/hw_renderhacks.cpp
index 05770125d..8f3325f2d 100644
--- a/src/hwrenderer/scene/hw_renderhacks.cpp
+++ b/src/hwrenderer/scene/hw_renderhacks.cpp
@@ -54,7 +54,8 @@ int HWDrawInfo::SetupLightsForOtherPlane(subsector_t * sub, FDynLightData &light
 	if (level.HasDynamicLights && !isFullbrightScene())
 	{
 		Plane p;
-		FLightNode * node = sub->sector->lighthead;
+
+		FLightNode * node = sub->section->lighthead;
 
 		lightdata.Clear();
 		while (node)
diff --git a/src/hwrenderer/scene/hw_spritelight.cpp b/src/hwrenderer/scene/hw_spritelight.cpp
index 3b5a0c1d8..a0d76343b 100644
--- a/src/hwrenderer/scene/hw_spritelight.cpp
+++ b/src/hwrenderer/scene/hw_spritelight.cpp
@@ -131,11 +131,11 @@ void HWDrawInfo::GetDynSpriteLight(AActor *thing, particle_t *particle, float *o
 {
 	if (thing != NULL)
 	{
-		GetDynSpriteLight(thing, (float)thing->X(), (float)thing->Y(), (float)thing->Center(), thing->Sector->lighthead, thing->Sector->PortalGroup, out);
+		GetDynSpriteLight(thing, (float)thing->X(), (float)thing->Y(), (float)thing->Center(), thing->section->lighthead, thing->Sector->PortalGroup, out);
 	}
 	else if (particle != NULL)
 	{
-		GetDynSpriteLight(NULL, (float)particle->Pos.X, (float)particle->Pos.Y, (float)particle->Pos.Z, particle->subsector->sector->lighthead, particle->subsector->sector->PortalGroup, out);
+		GetDynSpriteLight(NULL, (float)particle->Pos.X, (float)particle->Pos.Y, (float)particle->Pos.Z, particle->subsector->section->lighthead, particle->subsector->sector->PortalGroup, out);
 	}
 }
 
@@ -157,10 +157,13 @@ void hw_GetDynModelLight(AActor *self, FDynLightData &modellightdata)
 		float y = (float)self->Y();
 		float z = (float)self->Center();
 		float radiusSquared = (float)(self->renderradius * self->renderradius);
+		dl_validcount++;
 
 		BSPWalkCircle(x, y, radiusSquared, [&](subsector_t *subsector) // Iterate through all subsectors potentially touched by actor
 		{
-			FLightNode * node = subsector->sector->lighthead;
+			auto section = subsector->section;
+			if (section->validcount == dl_validcount) return;	// already done from a previous subsector.
+			FLightNode * node = section->lighthead;
 			while (node) // check all lights touching a subsector
 			{
 				ADynamicLight *light = node->lightsource;
diff --git a/src/hwrenderer/scene/hw_walls.cpp b/src/hwrenderer/scene/hw_walls.cpp
index b782c54e9..b91c38ae1 100644
--- a/src/hwrenderer/scene/hw_walls.cpp
+++ b/src/hwrenderer/scene/hw_walls.cpp
@@ -302,7 +302,7 @@ void GLWall::SetupLights(HWDrawInfo *di, FDynLightData &lightdata)
 	else if (sub)
 	{
 		// Polobject segs cannot be checked per sidedef so use the subsector instead.
-		node = sub->sector->lighthead;
+		node = sub->section->lighthead;
 	}
 	else node = NULL;
 
diff --git a/src/p_maputl.cpp b/src/p_maputl.cpp
index 19c9496d3..008edb210 100644
--- a/src/p_maputl.cpp
+++ b/src/p_maputl.cpp
@@ -470,7 +470,7 @@ void AActor::LinkToWorld(FLinkContext *ctx, bool spawningmapthing, sector_t *sec
 
 	Sector = sector;
 	subsector = R_PointInSubsector(Pos());	// this is from the rendering nodes, not the gameplay nodes!
-	section = level.sections.SectionForSubsector(subsector->Index());
+	section = subsector->section;
 
 	if (!(flags & MF_NOSECTOR))
 	{
diff --git a/src/polyrenderer/scene/poly_model.cpp b/src/polyrenderer/scene/poly_model.cpp
index 78520826f..91c975d1e 100644
--- a/src/polyrenderer/scene/poly_model.cpp
+++ b/src/polyrenderer/scene/poly_model.cpp
@@ -70,7 +70,7 @@ void PolyModelRenderer::AddLights(AActor *actor)
 
 		BSPWalkCircle(x, y, radiusSquared, [&](subsector_t *subsector) // Iterate through all subsectors potentially touched by actor
 		{
-			FLightNode * node = subsector->sector->lighthead;
+			FLightNode * node = subsector->section->lighthead;
 			while (node) // check all lights touching a subsector
 			{
 				ADynamicLight *light = node->lightsource;
diff --git a/src/polyrenderer/scene/poly_plane.cpp b/src/polyrenderer/scene/poly_plane.cpp
index 076a334f9..18d24cfd7 100644
--- a/src/polyrenderer/scene/poly_plane.cpp
+++ b/src/polyrenderer/scene/poly_plane.cpp
@@ -275,7 +275,7 @@ void RenderPolyPlane::SetDynLights(PolyRenderThread *thread, PolyDrawArgs &args,
 		return;
 	}
 
-	FLightNode *light_list = sub->sector->lighthead;
+	FLightNode *light_list = sub->section->lighthead;
 
 	auto cameraLight = PolyCameraLight::Instance();
 	if ((cameraLight->FixedLightLevel() >= 0) || (cameraLight->FixedColormap() != nullptr))
diff --git a/src/polyrenderer/scene/poly_sprite.cpp b/src/polyrenderer/scene/poly_sprite.cpp
index 011fa67c6..122f518c6 100644
--- a/src/polyrenderer/scene/poly_sprite.cpp
+++ b/src/polyrenderer/scene/poly_sprite.cpp
@@ -381,7 +381,7 @@ void RenderPolySprite::SetDynlight(AActor *thing, PolyDrawArgs &args)
 	float lit_red = 0;
 	float lit_green = 0;
 	float lit_blue = 0;
-	auto node = thing->Sector->lighthead;
+	auto node = thing->section->lighthead;
 	while (node != nullptr)
 	{
 		ADynamicLight *light = node->lightsource;
diff --git a/src/r_defs.h b/src/r_defs.h
index 9f1e7c265..5163e8f83 100644
--- a/src/r_defs.h
+++ b/src/r_defs.h
@@ -51,6 +51,7 @@ struct FLinePortal;
 struct seg_t;
 struct sector_t;
 class AActor;
+struct FSection;
 
 #define MAXWIDTH 12000
 #define MAXHEIGHT 5000
@@ -1028,7 +1029,6 @@ public:
 
 	// killough 3/7/98: support flat heights drawn at another sector's heights
 	sector_t *heightsec;		// other sector, or NULL if no other sector
-	FLightNode *				lighthead;
 
 	uint32_t bottommap, midmap, topmap;	// killough 4/4/98: dynamic colormaps
 										// [RH] these can also be blend values if
@@ -1455,13 +1455,13 @@ struct subsector_t
 	FMiniBSP	*BSP;
 	seg_t		*firstline;
 	sector_t	*render_sector;
+	FSection	*section;
 	uint32_t	numlines;
 	uint16_t	flags;
-	uint16_t	sectorindex;
+	short		mapsection;
 
 	// subsector related GL data
 	int				validcount;
-	short			mapsection;
 	char			hacked;			// 1: is part of a render hack
 
 	void BuildPolyBSP();
diff --git a/src/r_utility.cpp b/src/r_utility.cpp
index 8de8727f1..77c685626 100644
--- a/src/r_utility.cpp
+++ b/src/r_utility.cpp
@@ -142,6 +142,7 @@ bool			setsizeneeded;
 
 unsigned int	R_OldBlend = ~0;
 int 			validcount = 1; 	// increment every time a check is made
+int 			dl_validcount = 1; 	// increment every time a check is made
 FCanvasTextureInfo *FCanvasTextureInfo::List;
 
 DVector3a view;
diff --git a/src/r_utility.h b/src/r_utility.h
index b18588ab9..e5ac4a2b8 100644
--- a/src/r_utility.h
+++ b/src/r_utility.h
@@ -66,6 +66,7 @@ extern FViewWindow r_viewwindow;
 extern int				setblocks;
 extern bool				r_NoInterpolate;
 extern int				validcount;
+extern int				dl_validcount;			// For use with FSection. validcount is in use by the renderer and any quick section exclusion needs another variable.
 
 extern angle_t			LocalViewAngle;			// [RH] Added to consoleplayer's angle
 extern int				LocalViewPitch;			// [RH] Used directly instead of consoleplayer's pitch
diff --git a/src/swrenderer/scene/r_opaque_pass.cpp b/src/swrenderer/scene/r_opaque_pass.cpp
index 987b89b5b..de6922500 100644
--- a/src/swrenderer/scene/r_opaque_pass.cpp
+++ b/src/swrenderer/scene/r_opaque_pass.cpp
@@ -558,7 +558,7 @@ namespace swrenderer
 				Fake3DOpaque::Normal,
 				0);
 
-			ceilingplane->AddLights(Thread, frontsector->lighthead);
+			ceilingplane->AddLights(Thread, sub->section->lighthead);
 		}
 
 		int adjusted_floorlightlevel = floorlightlevel;
@@ -598,7 +598,7 @@ namespace swrenderer
 				Fake3DOpaque::Normal,
 				0);
 
-			floorplane->AddLights(Thread, frontsector->lighthead);
+			floorplane->AddLights(Thread, sub->section->lighthead);
 		}
 
 		Add3DFloorPlanes(sub, frontsector, basecolormap, foggy, adjusted_ceilinglightlevel, adjusted_floorlightlevel);
@@ -742,7 +742,7 @@ namespace swrenderer
 						Fake3DOpaque::FakeFloor,
 						fakeAlpha);
 
-					floorplane3d->AddLights(Thread, tempsec.lighthead);
+					floorplane3d->AddLights(Thread, sub->section->lighthead);
 
 					FakeDrawLoop(sub, &tempsec, floorplane3d, nullptr, foggy, basecolormap, Fake3DOpaque::FakeFloor);
 				}
@@ -810,7 +810,7 @@ namespace swrenderer
 						Fake3DOpaque::FakeCeiling,
 						fakeAlpha);
 
-					ceilingplane3d->AddLights(Thread, tempsec.lighthead);
+					ceilingplane3d->AddLights(Thread, sub->section->lighthead);
 
 					FakeDrawLoop(sub, &tempsec, nullptr, ceilingplane3d, foggy, basecolormap, Fake3DOpaque::FakeCeiling);
 				}
diff --git a/src/swrenderer/things/r_model.cpp b/src/swrenderer/things/r_model.cpp
index a3ce1a5bb..2ee416973 100644
--- a/src/swrenderer/things/r_model.cpp
+++ b/src/swrenderer/things/r_model.cpp
@@ -111,7 +111,7 @@ namespace swrenderer
 
 			BSPWalkCircle(x, y, radiusSquared, [&](subsector_t *subsector) // Iterate through all subsectors potentially touched by actor
 			{
-				FLightNode * node = subsector->sector->lighthead;
+				FLightNode * node = subsector->section->lighthead;
 				while (node) // check all lights touching a subsector
 				{
 					ADynamicLight *light = node->lightsource;
diff --git a/src/swrenderer/things/r_sprite.cpp b/src/swrenderer/things/r_sprite.cpp
index 36e9ca89f..1251860d9 100644
--- a/src/swrenderer/things/r_sprite.cpp
+++ b/src/swrenderer/things/r_sprite.cpp
@@ -202,6 +202,7 @@ namespace swrenderer
 		// killough 3/27/98: save sector for special clipping later
 		vis->heightsec = heightsec;
 		vis->sector = thing->Sector;
+		vis->section = thing->section;
 
 		vis->depth = (float)tz;
 		vis->gpos = { (float)pos.X, (float)pos.Y, (float)pos.Z };
@@ -251,7 +252,7 @@ namespace swrenderer
 			float lit_red = 0;
 			float lit_green = 0;
 			float lit_blue = 0;
-			auto node = vis->sector->lighthead;
+			auto node = vis->section->lighthead;
 			while (node != nullptr)
 			{
 				ADynamicLight *light = node->lightsource;
diff --git a/src/swrenderer/things/r_visiblesprite.h b/src/swrenderer/things/r_visiblesprite.h
index b1ddebae7..37787a809 100644
--- a/src/swrenderer/things/r_visiblesprite.h
+++ b/src/swrenderer/things/r_visiblesprite.h
@@ -73,6 +73,7 @@ namespace swrenderer
 
 		FVector3 gpos = { 0.0f, 0.0f, 0.0f }; // origin in world coordinates
 		sector_t *sector = nullptr; // sector this sprite is in
+		FSection *section;
 
 		ColormapLight Light;
 		float Alpha = 0.0f;