diff --git a/src/gamedata/r_defs.h b/src/gamedata/r_defs.h
index a6f4c2c4f3b..663f3aa388d 100644
--- a/src/gamedata/r_defs.h
+++ b/src/gamedata/r_defs.h
@@ -1196,6 +1196,9 @@ enum
 	WALLF_ABSLIGHTING_BOTTOM 	= WALLF_ABSLIGHTING_TIER << 2,	// Bottom tier light is absolute instead of relative
 
 	WALLF_DITHERTRANS			= 8192,	// Render with dithering transparency shader (gets reset every frame)
+	WALLF_DITHERTRANS_TOP		= WALLF_DITHERTRANS << 0,	// Top tier (gets reset every frame)
+	WALLF_DITHERTRANS_MID		= WALLF_DITHERTRANS << 1,	// Mid tier (gets reset every frame)
+	WALLF_DITHERTRANS_BOTTOM	= WALLF_DITHERTRANS << 2,	// Bottom tier (gets reset every frame)
 };
 
 struct side_t
@@ -1271,6 +1274,8 @@ struct side_t
 	int numsegs;
 	int sidenum;
 
+	int dithertranscount;
+
 	int GetLightLevel (bool foggy, int baselight, int which, bool is3dlight=false, int *pfakecontrast_usedbygzdoom=NULL) const;
 
 	void SetLight(int16_t l)
diff --git a/src/rendering/hwrenderer/hw_entrypoint.cpp b/src/rendering/hwrenderer/hw_entrypoint.cpp
index e55c041a643..0252fbc40d3 100644
--- a/src/rendering/hwrenderer/hw_entrypoint.cpp
+++ b/src/rendering/hwrenderer/hw_entrypoint.cpp
@@ -167,6 +167,7 @@ sector_t* RenderViewpoint(FRenderViewpoint& mainvp, AActor* camera, IntRect* bou
 		bool iso_ortho = (camera->ViewPos != NULL) && (camera->ViewPos->Flags & VPSF_ORTHOGRAPHIC);
 		if (iso_ortho && (camera->ViewPos->Offset.Length() > 0)) inv_iso_dist = 1.0/camera->ViewPos->Offset.Length();
 		di->VPUniforms.mProjectionMatrix = eye.GetProjection(fov, ratio, fovratio * inv_iso_dist, iso_ortho);
+		di->ProjectionMatrix2 = eye.GetProjection(fov, ratio, fovratio, false); // Regular ol' perspective projection matrix
 
 		// Stereo mode specific viewpoint adjustment
 		vp.Pos += eye.GetViewShift(vp.HWAngles.Yaw.Degrees());
diff --git a/src/rendering/hwrenderer/scene/hw_bsp.cpp b/src/rendering/hwrenderer/scene/hw_bsp.cpp
index 2c1abdf7c13..3f834fcf6d2 100644
--- a/src/rendering/hwrenderer/scene/hw_bsp.cpp
+++ b/src/rendering/hwrenderer/scene/hw_bsp.cpp
@@ -287,15 +287,17 @@ void HWDrawInfo::AddLine (seg_t *seg, bool portalclip)
 	auto &clipperr = *rClipper;
 	angle_t startAngleR = clipperr.PointToPseudoAngle(seg->v2->fX(), seg->v2->fY());
 	angle_t endAngleR = clipperr.PointToPseudoAngle(seg->v1->fX(), seg->v1->fY());
+	angle_t paddingR = 0x00200000; // Make radar clipping more aggressive (reveal less)
 
 	if(Viewpoint.IsAllowedOoB() && r_radarclipper && !(Level->flags3 & LEVEL3_NOFOGOFWAR) && (startAngleR - endAngleR >= ANGLE_180))
 	{
-		if (!seg->backsector) clipperr.SafeAddClipRange(startAngleR, endAngleR);
+		if (!seg->backsector) clipperr.SafeAddClipRange(startAngleR - paddingR, endAngleR + paddingR);
 		else if((seg->sidedef != nullptr) && !uint8_t(seg->sidedef->Flags & WALLF_POLYOBJ) && (currentsector->sectornum != seg->backsector->sectornum))
 		{
 			if (in_area == area_default) in_area = hw_CheckViewArea(seg->v1, seg->v2, seg->frontsector, seg->backsector);
 			backsector = hw_FakeFlat(seg->backsector, in_area, true);
-			if (hw_CheckClip(seg->sidedef, currentsector, backsector)) clipperr.SafeAddClipRange(startAngleR, endAngleR);
+			if (hw_CheckClip(seg->sidedef, currentsector, backsector)) clipperr.SafeAddClipRange(startAngleR - paddingR, endAngleR + paddingR);
+			backsector = nullptr;
 		}
 	}
 
@@ -313,7 +315,7 @@ void HWDrawInfo::AddLine (seg_t *seg, bool portalclip)
 			{
 			  currentsubsector->flags |= SSECMF_DRAWN;
 			}
-			if ((r_radarclipper || !(Level->flags3 & LEVEL3_NOFOGOFWAR)) && clipperr.SafeCheckRange(startAngleR, endAngleR))
+			if (Viewpoint.IsAllowedOoB() && (r_radarclipper && !(Level->flags3 & LEVEL3_NOFOGOFWAR)) && clipperr.SafeCheckRange(startAngleR, endAngleR))
 			{
 			  currentsubsector->flags |= SSECMF_DRAWN;
 			}
@@ -326,31 +328,7 @@ void HWDrawInfo::AddLine (seg_t *seg, bool portalclip)
 		return;
 	}
 
-	if (Viewpoint.IsAllowedOoB()) // No need for vertical clipping if viewpoint not allowed out of bounds
-	{
-		auto &clipperv = *vClipper;
-		angle_t startPitch = clipperv.PointToPseudoPitch(seg->v1->fX(), seg->v1->fY(), currentsector->floorplane.ZatPoint(seg->v1));
-		angle_t endPitch = clipperv.PointToPseudoPitch(seg->v1->fX(), seg->v1->fY(), currentsector->ceilingplane.ZatPoint(seg->v1));
-		angle_t startPitch2 = clipperv.PointToPseudoPitch(seg->v2->fX(), seg->v2->fY(), currentsector->floorplane.ZatPoint(seg->v2));
-		angle_t endPitch2 = clipperv.PointToPseudoPitch(seg->v2->fX(), seg->v2->fY(), currentsector->ceilingplane.ZatPoint(seg->v2));
-		angle_t temp;
-		// Wall can be tilted from viewpoint perspective. Find vertical extent on screen in psuedopitch units (0 to 2, bottom to top)
-		if(int(startPitch) > int(startPitch2)) // Handle zero crossing
-		{
-			temp = startPitch; startPitch = startPitch2; startPitch2 = temp; // exchange
-		}
-		if(int(endPitch) > int(endPitch2)) // Handle zero crossing
-		{
-			temp = endPitch; endPitch = endPitch2; endPitch2 = temp; // exchange
-		}
-
-		if (!clipperv.SafeCheckRange(startPitch, endPitch2))
-		{
-			return;
-		}
-	}
-
-	if (!r_radarclipper || (Level->flags3 & LEVEL3_NOFOGOFWAR) || clipperr.SafeCheckRange(startAngleR, endAngleR))
+	if (Viewpoint.IsAllowedOoB() && (!r_radarclipper || (Level->flags3 & LEVEL3_NOFOGOFWAR) || clipperr.SafeCheckRange(startAngleR, endAngleR)))
 		currentsubsector->flags |= SSECMF_DRAWN;
 
 	uint8_t ispoly = uint8_t(seg->sidedef->Flags & WALLF_POLYOBJ);
@@ -358,7 +336,7 @@ void HWDrawInfo::AddLine (seg_t *seg, bool portalclip)
 	if (!seg->backsector)
 	{
 		if(!Viewpoint.IsAllowedOoB())
-			if (!(seg->sidedef->Flags & WALLF_DITHERTRANS)) clipper.SafeAddClipRange(startAngle, endAngle);
+			if (!(seg->sidedef->Flags & WALLF_DITHERTRANS_MID)) clipper.SafeAddClipRange(startAngle, endAngle);
 	}
 	else if (!ispoly)	// Two-sided polyobjects never obstruct the view
 	{
@@ -385,7 +363,7 @@ void HWDrawInfo::AddLine (seg_t *seg, bool portalclip)
 
 			if (hw_CheckClip(seg->sidedef, currentsector, backsector))
 			{
-				if(!Viewpoint.IsAllowedOoB() && !(seg->sidedef->Flags & WALLF_DITHERTRANS))
+				if(!Viewpoint.IsAllowedOoB() && !(seg->sidedef->Flags & WALLF_DITHERTRANS_MID))
 					clipper.SafeAddClipRange(startAngle, endAngle);
 			}
 		}
@@ -729,8 +707,8 @@ void HWDrawInfo::DoSubsector(subsector_t * sub)
 
 	if(Viewpoint.IsAllowedOoB() && sector->isSecret() && sector->wasSecret() && !r_radarclipper) return;
 
-	// cull everything if subsector outside vertical clipper
-	if ((sub->polys == nullptr) && (!Viewpoint.IsOrtho() || !((Level->flags3 & LEVEL3_NOFOGOFWAR) || !r_radarclipper)))
+	// cull everything if subsector outside all relevant clippers
+	if ((sub->polys == nullptr))
 	{
 		auto &clipper = *mClipper;
 		auto &clipperv = *vClipper;
@@ -739,7 +717,10 @@ void HWDrawInfo::DoSubsector(subsector_t * sub)
 		seg_t * seg = sub->firstline;
 		bool anglevisible = false;
 		bool pitchvisible = !(Viewpoint.IsAllowedOoB()); // No vertical clipping if viewpoint is not allowed out of bounds
-		bool radarvisible = false;
+		bool radarvisible = !(Viewpoint.IsAllowedOoB()) || !r_radarclipper || (Level->flags3 & LEVEL3_NOFOGOFWAR) || ((sub->flags & SSECMF_DRAWN) && !deathmatch);
+		bool ceilreflect = (mCurrentPortal && strcmp(mCurrentPortal->GetName(), "Planemirror ceiling"));
+		bool floorreflect = (mCurrentPortal && strcmp(mCurrentPortal->GetName(), "Planemirror floor"));
+		double planez = (ceilreflect ? sector->ceilingplane.ZatPoint(Viewpoint.Pos) : sector->floorplane.ZatPoint(Viewpoint.Pos));
 		angle_t pitchtemp;
 		angle_t pitchmin = ANGLE_90;
 		angle_t pitchmax = 0;
@@ -748,25 +729,43 @@ void HWDrawInfo::DoSubsector(subsector_t * sub)
 		{
 			if((seg->v1 != nullptr) && (seg->v2 != nullptr))
 			{
-				angle_t startAngle = clipper.GetClipAngle(seg->v2);
-				angle_t endAngle = clipper.GetClipAngle(seg->v1);
-				if (startAngle-endAngle >= ANGLE_180) anglevisible |= clipper.SafeCheckRange(startAngle, endAngle);
-				angle_t startAngleR = clipperr.PointToPseudoAngle(seg->v2->fX(), seg->v2->fY());
-				angle_t endAngleR = clipperr.PointToPseudoAngle(seg->v1->fX(), seg->v1->fY());
-				if (startAngleR-endAngleR >= ANGLE_180)
-					radarvisible |= (clipperr.SafeCheckRange(startAngleR, endAngleR) || (Level->flags3 & LEVEL3_NOFOGOFWAR) || ((sub->flags & SSECMF_DRAWN) && !deathmatch));
+				if (!anglevisible)
+				{
+					angle_t startAngle = clipper.GetClipAngle(seg->v2);
+					angle_t endAngle = clipper.GetClipAngle(seg->v1);
+					if (startAngle-endAngle >= ANGLE_180) anglevisible |= clipper.SafeCheckRange(startAngle, endAngle);
+				}
+				if (!radarvisible)
+				{
+					angle_t startAngleR = clipperr.PointToPseudoAngle(seg->v2->fX(), seg->v2->fY());
+					angle_t endAngleR = clipperr.PointToPseudoAngle(seg->v1->fX(), seg->v1->fY());
+					if (startAngleR-endAngleR >= ANGLE_180) radarvisible |= clipperr.SafeCheckRange(startAngleR, endAngleR);
+				}
+
 				if (!pitchvisible)
 				{
-					pitchmin = clipperv.PointToPseudoPitch(seg->v1->fX(), seg->v1->fY(), sector->floorplane.ZatPoint(seg->v1));
-					pitchmax = clipperv.PointToPseudoPitch(seg->v1->fX(), seg->v1->fY(), sector->ceilingplane.ZatPoint(seg->v1));
+					pitchmin = clipperv.PointToPseudoPitch(seg->v1->fX(), seg->v1->fY(),
+														   (ceilreflect || floorreflect) ?
+														   2 * planez - sector->floorplane.ZatPoint(seg->v1) :
+														   sector->floorplane.ZatPoint(seg->v1));
+					pitchmax = clipperv.PointToPseudoPitch(seg->v1->fX(), seg->v1->fY(),
+														   (ceilreflect || floorreflect) ?
+														   2 * planez - sector->ceilingplane.ZatPoint(seg->v1) :
+														   sector->ceilingplane.ZatPoint(seg->v1));
 					pitchvisible |= clipperv.SafeCheckRange(pitchmin, pitchmax);
 				}
 				if (pitchvisible && anglevisible && radarvisible) break;
 				if (!pitchvisible)
 				{
-					pitchtemp = clipperv.PointToPseudoPitch(seg->v2->fX(), seg->v2->fY(), sector->floorplane.ZatPoint(seg->v2));
+					pitchtemp = clipperv.PointToPseudoPitch(seg->v2->fX(), seg->v2->fY(),
+															(ceilreflect || floorreflect) ?
+															2 * planez - sector->floorplane.ZatPoint(seg->v2) :
+															sector->floorplane.ZatPoint(seg->v2));
 					if (int(pitchmin) > int(pitchtemp)) pitchmin = pitchtemp;
-					pitchtemp = clipperv.PointToPseudoPitch(seg->v2->fX(), seg->v2->fY(), sector->ceilingplane.ZatPoint(seg->v2));
+					pitchtemp = clipperv.PointToPseudoPitch(seg->v2->fX(), seg->v2->fY(),
+															(ceilreflect || floorreflect) ?
+															2 * planez - sector->ceilingplane.ZatPoint(seg->v2) :
+															sector->ceilingplane.ZatPoint(seg->v2));
 					if (int(pitchmax) < int(pitchtemp)) pitchmax = pitchtemp;
 					pitchvisible |= clipperv.SafeCheckRange(pitchmin, pitchmax);
 				}
@@ -835,7 +834,7 @@ void HWDrawInfo::DoSubsector(subsector_t * sub)
 				SetupSprite.Unclock();
 			}
 		}
-		if (r_dithertransparency && Viewpoint.IsAllowedOoB() && (RTnum < MAXDITHERACTORS))
+		if (r_dithertransparency && Viewpoint.IsAllowedOoB() && (RTnum < MAXDITHERACTORS) && mCurrentPortal == nullptr)
 		{
 			// [DVR] Not parallelizable due to variables RTnum and RenderedTargets[]
 			for (auto p = sector->touching_renderthings; p != nullptr; p = p->m_snext)
@@ -988,8 +987,8 @@ void HWDrawInfo::RenderOrthoNoFog()
 {
 	if (Viewpoint.IsOrtho() && ((Level->flags3 & LEVEL3_NOFOGOFWAR) || !r_radarclipper))
 	{
-		double vxdbl = Viewpoint.camera->X();
-		double vydbl = Viewpoint.camera->Y();
+		double vxdbl = Viewpoint.OffPos.X;
+		double vydbl = Viewpoint.OffPos.Y;
 		double ext = Viewpoint.camera->ViewPos->Offset.Length() ?
 			3.0 * Viewpoint.camera->ViewPos->Offset.Length() * tan (Viewpoint.FieldOfView.Radians()*0.5) : 100.0;
 		FBoundingBox viewbox(vxdbl, vydbl, ext);
@@ -1014,16 +1013,8 @@ void HWDrawInfo::RenderBSP(void *node, bool drawpsprites)
 	viewy = FLOAT2FIXED(Viewpoint.Pos.Y);
 	if (r_radarclipper && !(Level->flags3 & LEVEL3_NOFOGOFWAR) && Viewpoint.IsAllowedOoB())
 	{
-		if (Viewpoint.camera->tracer != NULL)
-		{
-			viewx = FLOAT2FIXED(Viewpoint.camera->tracer->X());
-			viewy = FLOAT2FIXED(Viewpoint.camera->tracer->Y());
-		}
-		else
-		{
-			viewx = FLOAT2FIXED(Viewpoint.camera->X());
-			viewy = FLOAT2FIXED(Viewpoint.camera->Y());
-		}
+		viewx = FLOAT2FIXED(Viewpoint.OffPos.X);
+		viewy = FLOAT2FIXED(Viewpoint.OffPos.Y);
 	}
 
 	validcount++;	// used for processing sidedefs only once by the renderer.
diff --git a/src/rendering/hwrenderer/scene/hw_clipper.cpp b/src/rendering/hwrenderer/scene/hw_clipper.cpp
index 059a3998187..7444af30993 100644
--- a/src/rendering/hwrenderer/scene/hw_clipper.cpp
+++ b/src/rendering/hwrenderer/scene/hw_clipper.cpp
@@ -394,18 +394,10 @@ angle_t Clipper::PointToPseudoAngle(double x, double y)
 {
 	double vecx = x - viewpoint->Pos.X;
 	double vecy = y - viewpoint->Pos.Y;
-	if ((viewpoint->camera != NULL) && amRadar)
+	if (amRadar)
 	{
-		if (viewpoint->camera->tracer != NULL)
-		{
-			vecx = x - viewpoint->camera->tracer->X();
-			vecy = y - viewpoint->camera->tracer->Y();
-		}
-		else
-		{
-			vecx = x - viewpoint->camera->X();
-			vecy = y - viewpoint->camera->Y();
-		}
+		vecx = x - viewpoint->OffPos.X;
+		vecy = y - viewpoint->OffPos.Y;
 	}
 
 	if (vecx == 0 && vecy == 0)
@@ -467,7 +459,7 @@ angle_t Clipper::PointToPseudoPitch(double x, double y, double z)
 
 angle_t Clipper::PointToPseudoOrthoAngle(double x, double y)
 {
-	DVector3 disp = DVector3( x, y, 0 ) - viewpoint->camera->Pos();
+	DVector3 disp = DVector3(x, y, 0) - viewpoint->OffPos;
 	if (viewpoint->camera->ViewPos->Offset.XY().Length() == 0)
 	{
 		return AngleToPseudo( viewpoint->Angles.Yaw.BAMs() );
@@ -491,7 +483,7 @@ angle_t Clipper::PointToPseudoOrthoAngle(double x, double y)
 
 angle_t Clipper::PointToPseudoOrthoPitch(double x, double y, double z)
 {
-	DVector3 disp = DVector3( x, y, z ) - viewpoint->camera->Pos();
+	DVector3 disp = DVector3(x, y, z) - viewpoint->OffPos;
 	if (viewpoint->camera->ViewPos->Offset.XY().Length() > 0)
 	{
 		double yproj = viewpoint->PitchSin * disp.XY().Length() * deltaangle(disp.Angle(), viewpoint->Angles.Yaw).Cos();
diff --git a/src/rendering/hwrenderer/scene/hw_drawinfo.cpp b/src/rendering/hwrenderer/scene/hw_drawinfo.cpp
index 3453b6e500e..4042039336c 100644
--- a/src/rendering/hwrenderer/scene/hw_drawinfo.cpp
+++ b/src/rendering/hwrenderer/scene/hw_drawinfo.cpp
@@ -160,6 +160,7 @@ void HWDrawInfo::StartScene(FRenderViewpoint &parentvp, HWViewpointUniforms *uni
 		VPUniforms.mProjectionMatrix.loadIdentity();
 		VPUniforms.mViewMatrix.loadIdentity();
 		VPUniforms.mNormalViewMatrix.loadIdentity();
+		ProjectionMatrix2.loadIdentity();
 		VPUniforms.mViewHeight = viewheight;
 		if (lightmode == ELightMode::Build)
 		{
@@ -684,24 +685,88 @@ void HWDrawInfo::DrawCorona(FRenderState& state, ACorona* corona, double dist)
 
 static ETraceStatus TraceCallbackForDitherTransparency(FTraceResults& res, void* userdata)
 {
-	int* count = (int*)userdata;
+	BitArray* CurMapSections = (BitArray*)userdata;
 	double bf, bc;
-	(*count)++;
+
 	switch(res.HitType)
 	{
 	case TRACE_HitWall:
-		if (!(res.Line->sidedef[res.Side]->Flags & WALLF_DITHERTRANS))
 		{
-			bf = res.Line->sidedef[res.Side]->sector->floorplane.ZatPoint(res.HitPos.XY());
-			bc = res.Line->sidedef[res.Side]->sector->ceilingplane.ZatPoint(res.HitPos.XY());
-			if ((res.HitPos.Z <= bc) && (res.HitPos.Z >= bf)) res.Line->sidedef[res.Side]->Flags |= WALLF_DITHERTRANS;
+			sector_t* linesec = res.Line->sidedef[res.Side]->sector;
+			if (linesec->subsectorcount > 0 && (*CurMapSections)[linesec->subsectors[0]->mapsection])
+			{
+				bf = res.Line->sidedef[res.Side]->sector->floorplane.ZatPoint(res.HitPos.XY());
+				bc = res.Line->sidedef[res.Side]->sector->ceilingplane.ZatPoint(res.HitPos.XY());
+				if (res.Line->sidedef[!res.Side])
+				{
+					// Two sided line! So let's find out if mid, top, or bottom texture needs dithered transparency
+					bf = max(bf, res.Line->sidedef[!res.Side]->sector->floorplane.ZatPoint(res.HitPos.XY()));
+					bc = min(bc, res.Line->sidedef[!res.Side]->sector->ceilingplane.ZatPoint(res.HitPos.XY()));
+					if (res.HitPos.Z <= bf) res.Line->sidedef[res.Side]->Flags |= WALLF_DITHERTRANS_BOTTOM;
+					else if (res.HitPos.Z < bc) res.Line->sidedef[res.Side]->Flags |= WALLF_DITHERTRANS_MID;
+					else res.Line->sidedef[res.Side]->Flags |= WALLF_DITHERTRANS_TOP;
+
+					res.Line->sidedef[res.Side]->dithertranscount = max<int>(1, res.Line->sidedef[!res.Side]->sector->e->XFloor.ffloors.Size());
+				}
+				else if ((res.HitPos.Z <= bc) && (res.HitPos.Z >= bf))
+				{
+					res.Line->sidedef[res.Side]->Flags |= WALLF_DITHERTRANS_MID;
+					res.Line->sidedef[res.Side]->dithertranscount = 1;
+				}
+			}
 		}
 		break;
 	case TRACE_HitFloor:
-		res.Sector->floorplane.dithertransflag = true;
+		if (res.Sector->subsectorcount > 0 && (*CurMapSections)[res.Sector->subsectors[0]->mapsection] && res.HitVector.dot(res.Sector->floorplane.Normal()) < 0.0)
+		{
+			if (res.HitPos.Z == res.Sector->floorplane.ZatPoint(res.HitPos))
+			{
+				res.Sector->floorplane.dithertransflag = true;
+			}
+			else if (res.Sector->e->XFloor.ffloors.Size()) // Maybe it was 3D floors
+			{
+				F3DFloor *rover;
+				int kk;
+				for (kk = 0; kk < (int)res.Sector->e->XFloor.ffloors.Size(); kk++)
+				{
+					rover = res.Sector->e->XFloor.ffloors[kk];
+					if ((rover->flags&(FF_EXISTS | FF_RENDERPLANES | FF_THISINSIDE)) == (FF_EXISTS | FF_RENDERPLANES))
+					{
+						if (res.HitPos.Z == rover->top.plane->ZatPoint(res.HitPos))
+						{
+							rover->top.plane->dithertransflag = true;
+							break; // Out of for loop
+						}
+					}
+				}
+			}
+		}
 		break;
 	case TRACE_HitCeiling:
-		res.Sector->ceilingplane.dithertransflag = true;
+		if (res.Sector->subsectorcount > 0 && (*CurMapSections)[res.Sector->subsectors[0]->mapsection] && res.HitVector.dot(res.Sector->ceilingplane.Normal()) < 0.0)
+		{
+			if (res.HitPos.Z == res.Sector->ceilingplane.ZatPoint(res.HitPos))
+			{
+				res.Sector->ceilingplane.dithertransflag = true;
+			}
+			else if (res.Sector->e->XFloor.ffloors.Size()) // Maybe it was 3D floors
+			{
+				F3DFloor *rover;
+				int kk;
+				for (kk = 0; kk < (int)res.Sector->e->XFloor.ffloors.Size(); kk++)
+				{
+					rover = res.Sector->e->XFloor.ffloors[kk];
+					if ((rover->flags&(FF_EXISTS | FF_RENDERPLANES | FF_THISINSIDE)) == (FF_EXISTS | FF_RENDERPLANES))
+					{
+						if (res.HitPos.Z == rover->bottom.plane->ZatPoint(res.HitPos))
+						{
+							rover->bottom.plane->dithertransflag = true;
+							break; // Out of for loop
+						}
+					}
+				}
+			}
+		}
 		break;
 	case TRACE_HitActor:
 	default:
@@ -714,6 +779,7 @@ static ETraceStatus TraceCallbackForDitherTransparency(FTraceResults& res, void*
 
 void HWDrawInfo::SetDitherTransFlags(AActor* actor)
 {
+	// This should really be moved to a shader and have the GPU do some shape-tracing.
 	if (actor && actor->Sector)
 	{
 		FTraceResults results;
@@ -723,13 +789,11 @@ void HWDrawInfo::SetDitherTransFlags(AActor* actor)
 		DVector3 vvec = actorpos - Viewpoint.Pos;
 		if (Viewpoint.IsOrtho())
 		{
-			vvec += Viewpoint.camera->Pos() - actorpos;
-			vvec *= 5.0; // Should be 4.0? (since zNear is behind screen by 3*dist in VREyeInfo::GetProjection())
+			vvec = 5.0 * Viewpoint.camera->ViewPos->Offset.Length() * Viewpoint.ViewVector3D; // Should be 4.0? (since zNear is behind screen by 3*dist in VREyeInfo::GetProjection())
 		}
 		double distance = vvec.Length() - actor->radius;
 		DVector3 campos = actorpos - vvec;
 		sector_t* startsec;
-		int count = 0;
 
 		vvec = vvec.Unit();
 		campos.X -= horix; campos.Y += horiy; campos.Z += actor->Height * 0.25;
@@ -737,13 +801,25 @@ void HWDrawInfo::SetDitherTransFlags(AActor* actor)
 		{
 			startsec = Level->PointInRenderSubsector(campos)->sector;
 			Trace(campos, startsec, vvec, distance,
-				  0, 0, actor, results, 0, TraceCallbackForDitherTransparency, &count);
+				  0, 0, actor, results, TRACE_PortalRestrict, TraceCallbackForDitherTransparency, &CurrentMapSections);
 			campos.Z += actor->Height * 0.5;
 			Trace(campos, startsec, vvec, distance,
-				  0, 0, actor, results, 0, TraceCallbackForDitherTransparency, &count);
+				  0, 0, actor, results, TRACE_PortalRestrict, TraceCallbackForDitherTransparency, &CurrentMapSections);
 			campos.Z -= actor->Height * 0.5;
 			campos.X += horix; campos.Y -= horiy;
 		}
+
+		// Tracers don't work on 3D floors when you are starting in the same sector (standing under them, for example)
+		if (actor->Sector->e->XFloor.ffloors.Size()) // 3D floor
+		{
+			F3DFloor *rover;
+			for (int kk = 0; kk < (int)actor->Sector->e->XFloor.ffloors.Size(); kk++)
+			{
+				rover = actor->Sector->e->XFloor.ffloors[kk];
+				rover->top.plane->dithertransflag = true;
+				rover->bottom.plane->dithertransflag = true;
+			}
+		}
 	}
 }
 
diff --git a/src/rendering/hwrenderer/scene/hw_drawinfo.h b/src/rendering/hwrenderer/scene/hw_drawinfo.h
index ce848e29710..e4cbeb98eb9 100644
--- a/src/rendering/hwrenderer/scene/hw_drawinfo.h
+++ b/src/rendering/hwrenderer/scene/hw_drawinfo.h
@@ -150,6 +150,7 @@ struct HWDrawInfo
 	Clipper *rClipper; // Radar clipper
 	FRenderViewpoint Viewpoint;
 	HWViewpointUniforms VPUniforms;	// per-viewpoint uniform state
+	VSMatrix ProjectionMatrix2;
 	TArray<HWPortal *> Portals;
 	TArray<HWDecal *> Decals[2];	// the second slot is for mirrors which get rendered in a separate pass.
 	TArray<HUDSprite> hudsprites;	// These may just be stored by value.
diff --git a/src/rendering/hwrenderer/scene/hw_flats.cpp b/src/rendering/hwrenderer/scene/hw_flats.cpp
index f423c73fce5..317ba939969 100644
--- a/src/rendering/hwrenderer/scene/hw_flats.cpp
+++ b/src/rendering/hwrenderer/scene/hw_flats.cpp
@@ -47,6 +47,7 @@
 #include "hw_drawstructs.h"
 #include "hw_renderstate.h"
 #include "texturemanager.h"
+#include "hw_viewpointbuffer.h"
 
 #ifdef _DEBUG
 CVAR(Int, gl_breaksec, -1, 0)
@@ -314,6 +315,7 @@ void HWFlat::DrawFlat(HWDrawInfo *di, FRenderState &state, bool translucent)
 	int rel = getExtraLight();
 
 	state.SetNormal(plane.plane.Normal().X, plane.plane.Normal().Z, plane.plane.Normal().Y);
+	double zshift = (plane.plane.Normal().Z > 0.0 ? 0.01f : -0.01f); // The HWPlaneMirrorPortal::DrawPortalStencil() z-fights with flats
 
 	SetColor(state, di->Level, di->lightmode, lightlevel, rel, di->isFullbrightScene(), Colormap, alpha);
 	SetFog(state, di->Level, di->lightmode, lightlevel, rel, di->isFullbrightScene(), &Colormap, false);
@@ -364,7 +366,11 @@ void HWFlat::DrawFlat(HWDrawInfo *di, FRenderState &state, bool translucent)
 			else state.AlphaFunc(Alpha_GEqual, 0.f);
 			state.SetMaterial(texture, UF_Texture, 0, CLAMP_NONE, NO_TRANSLATION, -1);
 			SetPlaneTextureRotation(state, &plane, texture);
+			di->VPUniforms.mViewMatrix.translate(0.0, zshift, 0.0);
+			screen->mViewpoints->SetViewpoint(state, &di->VPUniforms);
 			DrawSubsectors(di, state);
+			di->VPUniforms.mViewMatrix.translate(0.0, -zshift, 0.0);
+			screen->mViewpoints->SetViewpoint(state, &di->VPUniforms);
 			state.EnableTextureMatrix(false);
 		}
 		state.SetRenderStyle(DefaultRenderStyle());
@@ -518,7 +524,7 @@ void HWFlat::ProcessSector(HWDrawInfo *di, sector_t * frontsector, int which)
 	//
 	//
 	//
-	if (((which & SSRF_RENDERFLOOR) && frontsector->floorplane.ZatPoint(vp.Pos) <= vp.Pos.Z && (!section || !(section->flags & FSection::DONTRENDERFLOOR)))&& !(vp.IsOrtho() && (vp.PitchSin < 0.0)))
+	if ((which & SSRF_RENDERFLOOR) && (vp.IsOrtho() ? vp.ViewVector3D.dot(frontsector->floorplane.Normal()) < 0.0 : frontsector->floorplane.ZatPoint(vp.Pos) <= vp.Pos.Z) && (!section || !(section->flags & FSection::DONTRENDERFLOOR)))
 	{
 		// process the original floor first.
 
@@ -576,7 +582,7 @@ void HWFlat::ProcessSector(HWDrawInfo *di, sector_t * frontsector, int which)
 	//
 	// 
 	//
-	if (((which & SSRF_RENDERCEILING) && frontsector->ceilingplane.ZatPoint(vp.Pos) >= vp.Pos.Z && (!section || !(section->flags & FSection::DONTRENDERCEILING))) && !(vp.IsOrtho() && (vp.PitchSin > 0.0)))
+	if ((which & SSRF_RENDERCEILING) && (vp.IsOrtho() ? vp.ViewVector3D.dot(frontsector->ceilingplane.Normal()) < 0.0 : frontsector->ceilingplane.ZatPoint(vp.Pos) >= vp.Pos.Z) && (!section || !(section->flags & FSection::DONTRENDERCEILING)))
 	{
 		// process the original ceiling first.
 
@@ -661,7 +667,7 @@ void HWFlat::ProcessSector(HWDrawInfo *di, sector_t * frontsector, int which)
 					double ff_top = rover->top.plane->ZatPoint(sector->centerspot);
 					if (ff_top < lastceilingheight)
 					{
-						if (vp.Pos.Z <= rover->top.plane->ZatPoint(vp.Pos))
+						if ((vp.IsOrtho() ? vp.ViewVector3D.dot(rover->top.plane->Normal()) > 0.0 : vp.Pos.Z <= rover->top.plane->ZatPoint(vp.Pos)))
 						{
 							SetFrom3DFloor(rover, true, !!(rover->flags&FF_FOG));
 							Colormap.FadeColor = frontsector->Colormap.FadeColor;
@@ -675,7 +681,7 @@ void HWFlat::ProcessSector(HWDrawInfo *di, sector_t * frontsector, int which)
 					double ff_bottom = rover->bottom.plane->ZatPoint(sector->centerspot);
 					if (ff_bottom < lastceilingheight)
 					{
-						if (vp.Pos.Z <= rover->bottom.plane->ZatPoint(vp.Pos))
+						if ((vp.IsOrtho() ? vp.ViewVector3D.dot(rover->bottom.plane->Normal()) > 0.0 : vp.Pos.Z <= rover->bottom.plane->ZatPoint(vp.Pos)))
 						{
 							SetFrom3DFloor(rover, false, !(rover->flags&FF_FOG));
 							Colormap.FadeColor = frontsector->Colormap.FadeColor;
@@ -701,7 +707,7 @@ void HWFlat::ProcessSector(HWDrawInfo *di, sector_t * frontsector, int which)
 					double ff_bottom = rover->bottom.plane->ZatPoint(sector->centerspot);
 					if (ff_bottom > lastfloorheight || (rover->flags&FF_FIX))
 					{
-						if (vp.Pos.Z >= rover->bottom.plane->ZatPoint(vp.Pos))
+						if ((vp.IsOrtho() ? vp.ViewVector3D.dot(rover->bottom.plane->Normal()) > 0.0 : vp.Pos.Z >= rover->bottom.plane->ZatPoint(vp.Pos)))
 						{
 							SetFrom3DFloor(rover, false, !(rover->flags&FF_FOG));
 							Colormap.FadeColor = frontsector->Colormap.FadeColor;
@@ -722,7 +728,7 @@ void HWFlat::ProcessSector(HWDrawInfo *di, sector_t * frontsector, int which)
 					double ff_top = rover->top.plane->ZatPoint(sector->centerspot);
 					if (ff_top > lastfloorheight)
 					{
-						if (vp.Pos.Z >= rover->top.plane->ZatPoint(vp.Pos))
+						if ((vp.IsOrtho() ? vp.ViewVector3D.dot(rover->top.plane->Normal()) > 0.0 : vp.Pos.Z >= rover->top.plane->ZatPoint(vp.Pos)))
 						{
 							SetFrom3DFloor(rover, true, !!(rover->flags&FF_FOG));
 							Colormap.FadeColor = frontsector->Colormap.FadeColor;
diff --git a/src/rendering/hwrenderer/scene/hw_portal.cpp b/src/rendering/hwrenderer/scene/hw_portal.cpp
index b0ea3a8c9bc..7746aa33850 100644
--- a/src/rendering/hwrenderer/scene/hw_portal.cpp
+++ b/src/rendering/hwrenderer/scene/hw_portal.cpp
@@ -125,6 +125,7 @@ bool FPortalSceneState::RenderFirstSkyPortal(int recursion, HWDrawInfo *outer_di
 {
 	HWPortal * best = nullptr;
 	unsigned bestindex = 0;
+	bool usestencil = outer_di->Viewpoint.IsAllowedOoB();
 
 	// Find the one with the highest amount of lines.
 	// Normally this is also the one that saves the largest amount
@@ -145,7 +146,7 @@ bool FPortalSceneState::RenderFirstSkyPortal(int recursion, HWDrawInfo *outer_di
 			}
 
 			// If the portal area contains the current camera viewpoint, let's always use it because it's likely to give the largest area.
-			if (p->boundingBox.contains(outer_di->Viewpoint.Pos))
+			if (p->boundingBox.contains(usestencil ? outer_di->Viewpoint.OffPos : outer_di->Viewpoint.Pos))
 			{
 				best = p;
 				bestindex = i;
@@ -157,7 +158,14 @@ bool FPortalSceneState::RenderFirstSkyPortal(int recursion, HWDrawInfo *outer_di
 	if (best)
 	{
 		portals.Delete(bestindex);
-		RenderPortal(best, state, false, outer_di);
+		if (usestencil && ((strcmp(best->GetName(), "Sky") == 0) || (strcmp(best->GetName(), "Skybox") == 0)))
+		{
+			tempmatrix = outer_di->VPUniforms.mProjectionMatrix; // ensure perspective projection matrix for skies
+			outer_di->VPUniforms.mProjectionMatrix = outer_di->ProjectionMatrix2;
+		}
+		RenderPortal(best, state, usestencil, outer_di);
+		if (usestencil && ((strcmp(best->GetName(), "Sky") == 0) || (strcmp(best->GetName(), "Skybox") == 0)))
+			outer_di->VPUniforms.mProjectionMatrix = tempmatrix;
 		delete best;
 		return true;
 	}
@@ -325,6 +333,7 @@ void HWPortal::RemoveStencil(HWDrawInfo *di, FRenderState &state, bool usestenci
 	bool needdepth = NeedDepthBuffer();
 
 	// Restore the old view
+
 	auto &vp = di->Viewpoint;
 	if (vp.camera != nullptr) vp.camera->renderflags = (vp.camera->renderflags & ~RF_MAYBEINVISIBLE) | savedvisibility;
 
@@ -410,20 +419,23 @@ void HWScenePortalBase::ClearClipper(HWDrawInfo *di, Clipper *clipper)
 
 	// Set the clipper to the minimal visible area
 	clipper->SafeAddClipRange(0, 0xffffffff);
+	auto outvp = outer_di->Viewpoint;
+	DVector3 outPos = clipper->amRadar ? outvp.OffPos : outvp.Pos;
+	angle_t padding = clipper->amRadar ? 0x00200000 : 0x00000000; // Make radar clipping more aggressive (reveal less)
 	for (unsigned int i = 0; i < lines.Size(); i++)
 	{
-		DAngle startAngle = (DVector2(lines[i].glseg.x2, lines[i].glseg.y2) - outer_di->Viewpoint.Pos).Angle() + angleOffset;
-		DAngle endAngle = (DVector2(lines[i].glseg.x1, lines[i].glseg.y1) - outer_di->Viewpoint.Pos).Angle() + angleOffset;
+		DAngle startAngle = (DVector2(lines[i].glseg.x2, lines[i].glseg.y2) - outPos).Angle() + angleOffset;
+		DAngle endAngle = (DVector2(lines[i].glseg.x1, lines[i].glseg.y1) - outPos).Angle() + angleOffset;
 
 		if (deltaangle(endAngle, startAngle) < nullAngle)
 		{
-			clipper->SafeRemoveClipRangeRealAngles(startAngle.BAMs(), endAngle.BAMs());
+			clipper->SafeRemoveClipRangeRealAngles(startAngle.BAMs() + padding, endAngle.BAMs() - padding);
 		}
 	}
 
 	// and finally clip it to the visible area
 	angle_t a1 = di->FrustumAngle();
-	if (a1 < ANGLE_180) clipper->SafeAddClipRangeRealAngles(di->Viewpoint.Angles.Yaw.BAMs() + a1, di->Viewpoint.Angles.Yaw.BAMs() - a1);
+	if (!clipper->amRadar && a1 < ANGLE_180) clipper->SafeAddClipRangeRealAngles(di->Viewpoint.Angles.Yaw.BAMs() + a1, di->Viewpoint.Angles.Yaw.BAMs() - a1);
 
 	// lock the parts that have just been clipped out.
 	clipper->SetSilhouette();
@@ -608,6 +620,8 @@ bool HWLineToLinePortal::Setup(HWDrawInfo *di, FRenderState &rstate, Clipper *cl
 	P_TranslatePortalZ(origin, vp.Pos.Z);
 	P_TranslatePortalXY(origin, vp.Path[0].X, vp.Path[0].Y);
 	P_TranslatePortalXY(origin, vp.Path[1].X, vp.Path[1].Y);
+	P_TranslatePortalXY(origin, vp.OffPos.X, vp.OffPos.Y);
+	P_TranslatePortalZ(origin, vp.OffPos.Z);
 	if (!vp.showviewer && vp.camera != nullptr && P_PointOnLineSidePrecise(vp.Path[0], glport->lines[0]->mDestination) != P_PointOnLineSidePrecise(vp.Path[1], glport->lines[0]->mDestination))
 	{
 		double distp = (vp.Path[0] - vp.Path[1]).Length();
@@ -791,10 +805,18 @@ bool HWSectorStackPortal::Setup(HWDrawInfo *di, FRenderState &rstate, Clipper *c
 	vp.Pos += origin->mDisplacement;
 	vp.ActorPos += origin->mDisplacement;
 	vp.ViewActor = nullptr;
+	vp.OffPos += origin->mDisplacement;
 
 	// avoid recursions!
 	if (origin->plane != -1) screen->instack[origin->plane]++;
-
+	if (lines.Size() > 0)
+	{
+		flat.plane.GetFromSector(lines[0].sub->sector,
+								 lines[0].sub->sector->GetPortal(sector_t::ceiling)->mType & (PORTS_STACKEDSECTORTHING | PORTS_PORTAL | PORTS_LINKEDPORTAL) ?
+								 sector_t::ceiling : sector_t::floor);
+		di->SetClipHeight(flat.plane.plane.ZatPoint(vp.Pos),
+						  flat.plane.plane.Normal().Z > 0 ? -1.f : 1.f);
+	}
 	di->SetupView(rstate, vp.Pos.X, vp.Pos.Y, vp.Pos.Z, !!(state->MirrorFlag & 1), !!(state->PlaneMirrorFlag & 1));
 	SetupCoverage(di);
 	ClearClipper(di, clipper);
@@ -802,6 +824,7 @@ bool HWSectorStackPortal::Setup(HWDrawInfo *di, FRenderState &rstate, Clipper *c
 	// If the viewpoint is not within the portal, we need to invalidate the entire clip area.
 	// The portal will re-validate the necessary parts when its subsectors get traversed.
 	subsector_t *sub = di->Level->PointInRenderSubsector(vp.Pos);
+	if (vp.IsAllowedOoB()) sub = di->Level->PointInRenderSubsector(vp.OffPos);
 	if (!(di->ss_renderflags[sub->Index()] & SSRF_SEEN))
 	{
 		clipper->SafeAddClipRange(0, ANGLE_MAX);
@@ -811,6 +834,22 @@ bool HWSectorStackPortal::Setup(HWDrawInfo *di, FRenderState &rstate, Clipper *c
 }
 
 
+void HWSectorStackPortal::DrawPortalStencil(FRenderState &state, int pass)
+{
+	bool isceiling = planesused & (1 << sector_t::ceiling);
+	for (unsigned int i = 0; i < lines.Size(); i++)
+	{
+		flat.section = lines[i].sub->section;
+		flat.iboindex = lines[i].sub->sector->iboindex[isceiling ? sector_t::ceiling : sector_t::floor];
+		flat.plane.GetFromSector(lines[i].sub->sector, isceiling ? sector_t::ceiling : sector_t::floor);
+		// if (isceiling) flat.plane.plane.FlipVert(); // Doesn't do anything. Stencil is a screen-space projection
+
+		state.SetNormal(flat.plane.plane.Normal().X, flat.plane.plane.Normal().Z, flat.plane.plane.Normal().Y);
+		state.DrawIndexed(DT_Triangles, flat.iboindex + flat.section->vertexindex, flat.section->vertexcount, i == 0);
+	}
+}
+
+
 void HWSectorStackPortal::Shutdown(HWDrawInfo *di, FRenderState &rstate)
 {
 	if (origin->plane != -1) screen->instack[origin->plane]--;
@@ -858,12 +897,31 @@ bool HWPlaneMirrorPortal::Setup(HWDrawInfo *di, FRenderState &rstate, Clipper *c
 	state->PlaneMirrorFlag++;
 	di->SetClipHeight(planez, state->PlaneMirrorMode < 0 ? -1.f : 1.f);
 	di->SetupView(rstate, vp.Pos.X, vp.Pos.Y, vp.Pos.Z, !!(state->MirrorFlag & 1), !!(state->PlaneMirrorFlag & 1));
+	vp.ViewVector3D.Z = - vp.ViewVector3D.Z;
+	vp.OffPos.Z = 2 * planez - vp.OffPos.Z;
 	ClearClipper(di, clipper);
 
 	di->UpdateCurrentMapSection();
 	return true;
 }
 
+
+void HWPlaneMirrorPortal::DrawPortalStencil(FRenderState &state, int pass)
+{
+	bool isceiling = planesused & (1 << sector_t::ceiling);
+	for (unsigned int i = 0; i < lines.Size(); i++)
+	{
+		flat.section = lines[i].sub->section;
+		flat.iboindex = lines[i].sub->sector->iboindex[isceiling ? sector_t::ceiling : sector_t::floor];
+		flat.plane.GetFromSector(lines[i].sub->sector, isceiling ? sector_t::ceiling : sector_t::floor);
+		// if (isceiling) flat.plane.plane.FlipVert(); // Doesn't do anything. Stencil is a screen-space projection
+
+		state.SetNormal(flat.plane.plane.Normal().X, flat.plane.plane.Normal().Z, flat.plane.plane.Normal().Y);
+		state.DrawIndexed(DT_Triangles, flat.iboindex + flat.section->vertexindex, flat.section->vertexcount, i == 0);
+	}
+}
+
+
 void HWPlaneMirrorPortal::Shutdown(HWDrawInfo *di, FRenderState &rstate)
 {
 	auto state = mState;
diff --git a/src/rendering/hwrenderer/scene/hw_portal.h b/src/rendering/hwrenderer/scene/hw_portal.h
index 29481f9e32d..50034df6a95 100644
--- a/src/rendering/hwrenderer/scene/hw_portal.h
+++ b/src/rendering/hwrenderer/scene/hw_portal.h
@@ -59,13 +59,14 @@ class HWPortal
 	TArray<unsigned int> mPrimIndices;
 	unsigned int mTopCap = ~0u, mBottomCap = ~0u;
 
-	void DrawPortalStencil(FRenderState &state, int pass);
+	virtual void DrawPortalStencil(FRenderState &state, int pass);
 
 public:
 	FPortalSceneState * mState;
 	TArray<HWWall> lines;
 	BoundingRect boundingBox;
 	int planesused = 0;
+	HWFlat flat;
 
     HWPortal(FPortalSceneState *s, bool local = false) : mState(s), boundingBox(false)
     {
@@ -112,6 +113,8 @@ struct FPortalSceneState
 
 	int skyboxrecursion = 0;
 
+	VSMatrix tempmatrix;
+
 	void BeginScene()
 	{
 		UniqueSkies.Clear();
@@ -145,7 +148,7 @@ class HWScenePortalBase : public HWPortal
 	virtual bool NeedDepthBuffer() { return true; }
 	virtual void DrawContents(HWDrawInfo *di, FRenderState &state)
 	{
-		if (Setup(di, state, di->mClipper))
+		if (Setup(di, state, (di->Viewpoint.IsAllowedOoB() ? di->rClipper : di->mClipper)))
 		{
 			di->DrawScene(DM_PORTAL);
 			Shutdown(di, state);
@@ -267,6 +270,7 @@ struct HWSectorStackPortal : public HWScenePortalBase
 	TArray<subsector_t *> subsectors;
 protected:
 	bool Setup(HWDrawInfo *di, FRenderState &rstate, Clipper *clipper) override;
+	void DrawPortalStencil(FRenderState &state, int pass) override;
 	void Shutdown(HWDrawInfo *di, FRenderState &rstate) override;
 	virtual void * GetSource() const { return origin; }
 	virtual bool IsSky() { return true; }	// although this isn't a real sky it can be handled as one.
@@ -293,6 +297,7 @@ struct HWPlaneMirrorPortal : public HWScenePortalBase
 protected:
 	bool Setup(HWDrawInfo *di, FRenderState &rstate, Clipper *clipper) override;
 	void Shutdown(HWDrawInfo *di, FRenderState &rstate) override;
+	void DrawPortalStencil(FRenderState &state, int pass) override;
 	virtual void * GetSource() const { return origin; }
 	virtual const char *GetName();
 	secplane_t * origin;
diff --git a/src/rendering/hwrenderer/scene/hw_sky.cpp b/src/rendering/hwrenderer/scene/hw_sky.cpp
index 6d77a275d5d..2aef16c8f03 100644
--- a/src/rendering/hwrenderer/scene/hw_sky.cpp
+++ b/src/rendering/hwrenderer/scene/hw_sky.cpp
@@ -130,7 +130,6 @@ void HWSkyInfo::init(HWDrawInfo *di, sector_t* sec, int skypos, int sky1, PalEnt
 void HWWall::SkyPlane(HWWallDispatcher *di, sector_t *sector, int plane, bool allowreflect)
 {
 	int ptype = -1;
-	if (di->di && di->di->Viewpoint.IsAllowedOoB()) return; // Couldn't prevent sky portal occlusion. Skybox is bad in ortho too.
 
 	FSectorPortal *sportal = sector->ValidatePortal(plane);
 	if (sportal != nullptr && sportal->mFlags & PORTSF_INSKYBOX) sportal = nullptr;	// no recursions, delete it here to simplify the following code
@@ -155,11 +154,17 @@ void HWWall::SkyPlane(HWWallDispatcher *di, sector_t *sector, int plane, bool al
 		case PORTS_PORTAL:
 		case PORTS_LINKEDPORTAL:
 		{
+			if (di->di && di->di->Viewpoint.IsAllowedOoB())
+			{
+				secplane_t myplane = plane ? sector->ceilingplane : sector->floorplane;
+				if (di->di->Viewpoint.IsOrtho() && di->di->Viewpoint.ViewVector3D.dot(myplane.Normal()) > 0.0) return;
+				else if (plane==1 && di->di->Viewpoint.Pos.Z >= myplane.ZatPoint(di->di->Viewpoint.Pos)) return;
+				else if (plane==0 && di->di->Viewpoint.Pos.Z <= myplane.ZatPoint(di->di->Viewpoint.Pos)) return;
+			}
 			auto glport = sector->GetPortalGroup(plane);
 			if (glport != NULL)
 			{
 				if (sector->PortalBlocksView(plane)) return;
-
 				if (di->di && screen->instack[1 - plane]) return;
 				ptype = PORTALTYPE_SECTORSTACK;
 				portal = glport;
diff --git a/src/rendering/hwrenderer/scene/hw_walls.cpp b/src/rendering/hwrenderer/scene/hw_walls.cpp
index 5c5e357d559..d5271d05f1b 100644
--- a/src/rendering/hwrenderer/scene/hw_walls.cpp
+++ b/src/rendering/hwrenderer/scene/hw_walls.cpp
@@ -83,15 +83,31 @@ void SetSplitPlanes(FRenderState& state, const secplane_t& top, const secplane_t
 
 void HWWall::RenderWall(FRenderState &state, int textured)
 {
-	if (seg->sidedef->Flags & WALLF_DITHERTRANS) state.SetEffect(EFF_DITHERTRANS);
+	bool ditherT = (type == RENDERWALL_BOTTOM) && (seg->sidedef->Flags & WALLF_DITHERTRANS_BOTTOM);
+	ditherT |= (type == RENDERWALL_TOP) && (seg->sidedef->Flags & WALLF_DITHERTRANS_TOP);
+	ditherT |= seg->sidedef->Flags & WALLF_DITHERTRANS_MID;
+	if (ditherT)
+	{
+		state.SetEffect(EFF_DITHERTRANS);
+	}
 	assert(vertcount > 0);
 	state.SetLightIndex(dynlightindex);
 	state.Draw(DT_TriangleFan, vertindex, vertcount);
 	vertexcount += vertcount;
-	if (seg->sidedef->Flags & WALLF_DITHERTRANS)
+	if (ditherT)
 	{
 		state.SetEffect(EFF_NONE);
-		seg->sidedef->Flags &= ~WALLF_DITHERTRANS; // reset this every frame
+		switch(type) // reset this every frame
+		{
+		case RENDERWALL_TOP:
+			seg->sidedef->Flags &= ~WALLF_DITHERTRANS_TOP;
+			break;
+		case RENDERWALL_BOTTOM:
+			seg->sidedef->Flags &= ~WALLF_DITHERTRANS_BOTTOM;
+			break;
+		default:
+			if (seg->sidedef->dithertranscount-- <= 0) seg->sidedef->Flags &= ~WALLF_DITHERTRANS_MID;
+		}
 	}
 }
 
@@ -628,7 +644,8 @@ void HWWall::PutPortal(HWWallDispatcher *di, int ptype, int plane)
 			break;
 
 		case PORTALTYPE_PLANEMIRROR:
-			if (portalState.PlaneMirrorMode * planemirror->fC() <= 0)
+			if (ddi->Viewpoint.IsOrtho() ? (ddi->Viewpoint.ViewVector3D.dot(planemirror->Normal()) < 0)
+				: (portalState.PlaneMirrorMode * planemirror->fC() <= 0))
 			{
 				planemirror = portalState.UniquePlaneMirrors.Get(planemirror);
 				portal = ddi->FindPortal(planemirror);
@@ -2181,8 +2198,6 @@ void HWWall::Process(HWWallDispatcher *di, seg_t *seg, sector_t * frontsector, s
 	}
 
 	bool isportal = seg->linedef->isVisualPortal() && seg->sidedef == seg->linedef->sidedef[0];
-	// Don't render portal insides if in orthographic mode
-	if (di->di) isportal &= !(di->di->Viewpoint.IsOrtho());
 
 	//return;
 	// [GZ] 3D middle textures are necessarily two-sided, even if they lack the explicit two-sided flag
diff --git a/src/rendering/r_utility.cpp b/src/rendering/r_utility.cpp
index 3a3fdd70e7f..035ac6de7cf 100644
--- a/src/rendering/r_utility.cpp
+++ b/src/rendering/r_utility.cpp
@@ -550,8 +550,12 @@ void R_InterpolateView(FRenderViewpoint& viewPoint, const player_t* const player
 			const int prevPortalGroup = viewLvl->PointInRenderSubsector(iView->Old.Pos)->sector->PortalGroup;
 			const int curPortalGroup = viewLvl->PointInRenderSubsector(iView->New.Pos)->sector->PortalGroup;
 
-			const DVector2 portalOffset = viewLvl->Displacements.getOffset(prevPortalGroup, curPortalGroup);
-			viewPoint.Pos = iView->Old.Pos * inverseTicFrac + (iView->New.Pos - portalOffset) * ticFrac;
+			if (viewPoint.IsAllowedOoB() && prevPortalGroup != curPortalGroup) viewPoint.Pos = iView->New.Pos;
+			else
+			{
+				const DVector2 portalOffset = viewLvl->Displacements.getOffset(prevPortalGroup, curPortalGroup);
+				viewPoint.Pos = iView->Old.Pos * inverseTicFrac + (iView->New.Pos - portalOffset) * ticFrac;
+			}
 			viewPoint.Path[0] = viewPoint.Path[1] = iView->New.Pos;
 		}
 	}
@@ -704,6 +708,21 @@ void FRenderViewpoint::SetViewAngle(const FViewWindow& viewWindow)
 	ViewVector.X = v.X;
 	ViewVector.Y = v.Y;
 	HWAngles.Yaw = FAngle::fromDeg(270.0 - Angles.Yaw.Degrees());
+	ViewVector3D.X = v.X * PitchCos;
+	ViewVector3D.Y = v.Y * PitchCos;
+	ViewVector3D.Z = -PitchSin;
+
+	if (IsOrtho() || IsAllowedOoB()) // These auto-ensure that camera and camera->ViewPos exist
+	{
+		if (camera->tracer != NULL)
+		{
+			OffPos = camera->tracer->Pos();
+		}
+		else
+		{
+			OffPos = Pos + ViewVector3D * camera->ViewPos->Offset.Length();
+		}
+	}
 
 	if (IsOrtho() && (camera->ViewPos->Offset.XY().Length() > 0.0))
 	{
diff --git a/src/rendering/r_utility.h b/src/rendering/r_utility.h
index f7e4a1e1d34..0c2f47833ca 100644
--- a/src/rendering/r_utility.h
+++ b/src/rendering/r_utility.h
@@ -25,6 +25,8 @@ struct FRenderViewpoint
 	DRotator		Angles;			// Camera angles
 	FRotator		HWAngles;		// Actual rotation angles for the hardware renderer
 	DVector2		ViewVector;		// HWR only: direction the camera is facing.
+	DVector3		ViewVector3D;	// 3D direction the camera is facing.
+	DVector3        OffPos;         // Viewpoint position to use for Ortho and OoB calculations
 	AActor			*ViewActor;		// either the same as camera or nullptr
 	FLevelLocals	*ViewLevel;		// The level this viewpoint is on.