diff --git a/src/gl/data/gl_data.cpp b/src/gl/data/gl_data.cpp
index df5d0d35f..6ec57b055 100644
--- a/src/gl/data/gl_data.cpp
+++ b/src/gl/data/gl_data.cpp
@@ -157,8 +157,8 @@ int LS_Sector_SetPlaneReflection (line_t *ln, AActor *it, bool backSide,
 	while ((secnum = itr.Next()) >= 0)
 	{
 		sector_t * s = &sectors[secnum];
-		if (s->floorplane.a==0 && s->floorplane.b==0) s->reflect[sector_t::floor] = arg1/255.f;
-		if (s->ceilingplane.a==0 && s->ceilingplane.b==0) sectors[secnum].reflect[sector_t::ceiling] = arg2/255.f;
+		if (!s->floorplane.isSlope()) s->reflect[sector_t::floor] = arg1/255.f;
+		if (!s->ceilingplane.isSlope()) sectors[secnum].reflect[sector_t::ceiling] = arg2/255.f;
 	}
 
 	return true;
diff --git a/src/gl/data/gl_setup.cpp b/src/gl/data/gl_setup.cpp
index 3b879df7a..a13192694 100644
--- a/src/gl/data/gl_setup.cpp
+++ b/src/gl/data/gl_setup.cpp
@@ -324,7 +324,7 @@ static void PrepareTransparentDoors(sector_t * sector)
 	if (sector->subsectorcount==0) return;
 
 	sector->transdoorheight=sector->GetPlaneTexZ(sector_t::floor);
-	sector->transdoor= !(sector->e->XFloor.ffloors.Size() || sector->heightsec || sector->floorplane.a || sector->floorplane.b);
+	sector->transdoor= !(sector->e->XFloor.ffloors.Size() || sector->heightsec || sector->floorplane.isSlope());
 
 	if (sector->transdoor)
 	{
diff --git a/src/gl/renderer/gl_renderstate.h b/src/gl/renderer/gl_renderstate.h
index d46bb4996..87df78a6b 100644
--- a/src/gl/renderer/gl_renderstate.h
+++ b/src/gl/renderer/gl_renderstate.h
@@ -275,14 +275,14 @@ public:
 
 	void SetGlowPlanes(const secplane_t &top, const secplane_t &bottom)
 	{
-		mGlowTopPlane.Set(FIXED2FLOAT(top.a), FIXED2FLOAT(top.b), FIXED2FLOAT(top.ic), FIXED2FLOAT(top.d));
-		mGlowBottomPlane.Set(FIXED2FLOAT(bottom.a), FIXED2FLOAT(bottom.b), FIXED2FLOAT(bottom.ic), FIXED2FLOAT(bottom.d));
+		mGlowTopPlane.Set(top.fA(), top.fB(), 1. / top.fC(), top.fD());
+		mGlowBottomPlane.Set(bottom.fA(), bottom.fB(), 1. / bottom.fC(), bottom.fD());
 	}
 
 	void SetSplitPlanes(const secplane_t &top, const secplane_t &bottom)
 	{
-		mSplitTopPlane.Set(FIXED2FLOAT(top.a), FIXED2FLOAT(top.b), FIXED2FLOAT(top.ic), FIXED2FLOAT(top.d));
-		mSplitBottomPlane.Set(FIXED2FLOAT(bottom.a), FIXED2FLOAT(bottom.b), FIXED2FLOAT(bottom.ic), FIXED2FLOAT(bottom.d));
+		mSplitTopPlane.Set(top.fA(), top.fB(), 1. / top.fC(), top.fD());
+		mSplitBottomPlane.Set(bottom.fA(), bottom.fB(), 1. / bottom.fC(), bottom.fD());
 	}
 
 	void SetDynLight(float r, float g, float b)
diff --git a/src/gl/scene/gl_fakeflat.cpp b/src/gl/scene/gl_fakeflat.cpp
index 8399526da..101fcc8a3 100644
--- a/src/gl/scene/gl_fakeflat.cpp
+++ b/src/gl/scene/gl_fakeflat.cpp
@@ -80,44 +80,44 @@ bool gl_CheckClip(side_t * sidedef, sector_t * frontsector, sector_t * backsecto
 	// on large levels this distinction can save some time
 	// That's a lot of avoided multiplications if there's a lot to see!
 
-	if (frontsector->ceilingplane.a | frontsector->ceilingplane.b)
+	if (frontsector->ceilingplane.isSlope())
 	{
 		fs_ceilingheight1=frontsector->ceilingplane.ZatPoint(linedef->v1);
 		fs_ceilingheight2=frontsector->ceilingplane.ZatPoint(linedef->v2);
 	}
 	else
 	{
-		fs_ceilingheight2=fs_ceilingheight1=frontsector->ceilingplane.d;
+		fs_ceilingheight2=fs_ceilingheight1=frontsector->ceilingplane.fixD();
 	}
 
-	if (frontsector->floorplane.a | frontsector->floorplane.b)
+	if (frontsector->floorplane.isSlope())
 	{
 		fs_floorheight1=frontsector->floorplane.ZatPoint(linedef->v1);
 		fs_floorheight2=frontsector->floorplane.ZatPoint(linedef->v2);
 	}
 	else
 	{
-		fs_floorheight2=fs_floorheight1=-frontsector->floorplane.d;
+		fs_floorheight2=fs_floorheight1=-frontsector->floorplane.fixD();
 	}
 	
-	if (backsector->ceilingplane.a | backsector->ceilingplane.b)
+	if (backsector->ceilingplane.isSlope())
 	{
 		bs_ceilingheight1=backsector->ceilingplane.ZatPoint(linedef->v1);
 		bs_ceilingheight2=backsector->ceilingplane.ZatPoint(linedef->v2);
 	}
 	else
 	{
-		bs_ceilingheight2=bs_ceilingheight1=backsector->ceilingplane.d;
+		bs_ceilingheight2=bs_ceilingheight1=backsector->ceilingplane.fixD();
 	}
 
-	if (backsector->floorplane.a | backsector->floorplane.b)
+	if (backsector->floorplane.isSlope())
 	{
 		bs_floorheight1=backsector->floorplane.ZatPoint(linedef->v1);
 		bs_floorheight2=backsector->floorplane.ZatPoint(linedef->v2);
 	}
 	else
 	{
-		bs_floorheight2=bs_floorheight1=-backsector->floorplane.d;
+		bs_floorheight2=bs_floorheight1=-backsector->floorplane.fixD();
 	}
 
 	// now check for closed sectors!
@@ -206,7 +206,7 @@ sector_t * gl_FakeFlat(sector_t * sec, sector_t * dest, area_t in_area, bool bac
 		// visual glitches because upper amd lower textures overlap.
 		if (back && sec->planes[sector_t::floor].TexZ > sec->planes[sector_t::ceiling].TexZ)
 		{
-			if (!(sec->floorplane.a | sec->floorplane.b | sec->ceilingplane.a | sec->ceilingplane.b))
+			if (!sec->floorplane.isSlope() && !sec->ceilingplane.isSlope())
 			{
 				*dest = *sec;
 				dest->ceilingplane=sec->floorplane;
diff --git a/src/gl/scene/gl_flats.cpp b/src/gl/scene/gl_flats.cpp
index cffa1ee25..29602fbd2 100644
--- a/src/gl/scene/gl_flats.cpp
+++ b/src/gl/scene/gl_flats.cpp
@@ -174,7 +174,7 @@ void GLFlat::SetupSubsectorLights(int pass, subsector_t * sub, int *dli)
 void GLFlat::DrawSubsector(subsector_t * sub)
 {
 	FFlatVertex *ptr = GLRenderer->mVBO->GetBuffer();
-	if (plane.plane.a | plane.plane.b)
+	if (plane.plane.isSlope())
 	{
 		for (unsigned int k = 0; k < sub->numlines; k++)
 		{
diff --git a/src/gl/scene/gl_portal.cpp b/src/gl/scene/gl_portal.cpp
index 0fda331b4..1d69d2b99 100644
--- a/src/gl/scene/gl_portal.cpp
+++ b/src/gl/scene/gl_portal.cpp
@@ -810,7 +810,7 @@ void GLPlaneMirrorPortal::DrawContents()
 	fixed_t planez = origin->ZatPoint(viewx, viewy);
 	viewz = 2*planez - viewz;
 	GLRenderer->mViewActor = NULL;
-	PlaneMirrorMode = ksgn(origin->c);
+	PlaneMirrorMode = origin->fC() < 0 ? -1 : 1;
 	r_showviewer = true;
 
 	validcount++;
diff --git a/src/gl/scene/gl_renderhacks.cpp b/src/gl/scene/gl_renderhacks.cpp
index 2a3839037..972e970d5 100644
--- a/src/gl/scene/gl_renderhacks.cpp
+++ b/src/gl/scene/gl_renderhacks.cpp
@@ -296,7 +296,7 @@ bool FDrawInfo::DoOneSectorUpper(subsector_t * subsec, fixed_t planez)
 			sector_t * sec = gl_FakeFlat(seg->backsector, &fakesec, true);
 
 			// Don't bother with slopes
-			if (sec->ceilingplane.a!=0 || sec->ceilingplane.b!=0)  return false;
+			if (sec->ceilingplane.isSlope())  return false;
 
 			// Is the neighboring ceiling lower than the desired height?
 			if (sec->GetPlaneTexZ(sector_t::ceiling)<planez) 
@@ -354,7 +354,7 @@ bool FDrawInfo::DoOneSectorLower(subsector_t * subsec, fixed_t planez)
 			sector_t * sec = gl_FakeFlat(seg->backsector, &fakesec, true);
 
 			// Don't bother with slopes
-			if (sec->floorplane.a!=0 || sec->floorplane.b!=0)  return false;
+			if (sec->floorplane.isSlope())  return false;
 
 			// Is the neighboring floor higher than the desired height?
 			if (sec->GetPlaneTexZ(sector_t::floor)>planez) 
@@ -413,7 +413,7 @@ bool FDrawInfo::DoFakeBridge(subsector_t * subsec, fixed_t planez)
 			sector_t * sec = gl_FakeFlat(seg->backsector, &fakesec, true);
 
 			// Don't bother with slopes
-			if (sec->floorplane.a!=0 || sec->floorplane.b!=0)  return false;
+			if (sec->floorplane.isSlope())  return false;
 
 			// Is the neighboring floor higher than the desired height?
 			if (sec->GetPlaneTexZ(sector_t::floor)<planez) 
@@ -466,7 +466,7 @@ bool FDrawInfo::DoFakeCeilingBridge(subsector_t * subsec, fixed_t planez)
 			sector_t * sec = gl_FakeFlat(seg->backsector, &fakesec, true);
 
 			// Don't bother with slopes
-			if (sec->ceilingplane.a!=0 || sec->ceilingplane.b!=0)  return false;
+			if (sec->ceilingplane.isSlope())  return false;
 
 			// Is the neighboring ceiling higher than the desired height?
 			if (sec->GetPlaneTexZ(sector_t::ceiling)>planez) 
diff --git a/src/gl/scene/gl_sky.cpp b/src/gl/scene/gl_sky.cpp
index 3cedd38c3..3180b0ecf 100644
--- a/src/gl/scene/gl_sky.cpp
+++ b/src/gl/scene/gl_sky.cpp
@@ -173,8 +173,8 @@ void GLWall::SkyPlane(sector_t *sector, int plane, bool allowreflect)
 		}
 		else if (allowreflect && sector->GetReflect(plane) > 0)
 		{
-			if ((plane == sector_t::ceiling && viewz > sector->ceilingplane.d) ||
-				(plane == sector_t::floor && viewz < -sector->floorplane.d)) return;
+			if ((plane == sector_t::ceiling && viewz > sector->ceilingplane.fixD()) ||
+				(plane == sector_t::floor && viewz < -sector->floorplane.fixD())) return;
 			ptype = PORTALTYPE_PLANEMIRROR;
 			planemirror = plane == sector_t::ceiling ? &sector->ceilingplane : &sector->floorplane;
 		}
@@ -263,7 +263,7 @@ void GLWall::SkyTop(seg_t * seg,sector_t * fs,sector_t * bs,vertex_t * v1,vertex
 					return;
 
 			// one more check for some ugly transparent door hacks
-			if (bs->floorplane.a==0 && bs->floorplane.b==0 && fs->floorplane.a==0 && fs->floorplane.b==0)
+			if (!bs->floorplane.isSlope() && !fs->floorplane.isSlope())
 			{
 				if (bs->GetPlaneTexZ(sector_t::floor)==fs->GetPlaneTexZ(sector_t::floor)+FRACUNIT)
 				{
@@ -309,7 +309,7 @@ void GLWall::SkyTop(seg_t * seg,sector_t * fs,sector_t * bs,vertex_t * v1,vertex
 		if (frontreflect > 0)
 		{
 			float backreflect = bs->GetReflect(sector_t::ceiling);
-			if (backreflect > 0 && bs->ceilingplane.d == fs->ceilingplane.d)
+			if (backreflect > 0 && bs->ceilingplane.fD() == fs->ceilingplane.fD())
 			{
 				// Don't add intra-portal line to the portal.
 				return;
@@ -386,7 +386,7 @@ void GLWall::SkyBottom(seg_t * seg,sector_t * fs,sector_t * bs,vertex_t * v1,ver
 		if (frontreflect > 0)
 		{
 			float backreflect = bs->GetReflect(sector_t::floor);
-			if (backreflect > 0 && bs->floorplane.d == fs->floorplane.d)
+			if (backreflect > 0 && bs->floorplane.fD() == fs->floorplane.fD())
 			{
 				// Don't add intra-portal line to the portal.
 				return;
diff --git a/src/gl/scene/gl_sprite.cpp b/src/gl/scene/gl_sprite.cpp
index 80961ae6d..30d5baecc 100644
--- a/src/gl/scene/gl_sprite.cpp
+++ b/src/gl/scene/gl_sprite.cpp
@@ -240,8 +240,9 @@ void GLSprite::Draw(int pass)
 		if (lightlist)
 		{
 			// set up the light slice
-			static secplane_t bottommost = { 0, 0, FRACUNIT, 32767<<FRACBITS, FRACUNIT };
-			static secplane_t topmost = { 0, 0, FRACUNIT, -(32767<<FRACBITS), FRACUNIT };
+#pragma message ("Undo this!")
+			secplane_t bottommost; bottommost.set(0, 0, FRACUNIT, 32767 << FRACBITS);
+			secplane_t topmost; topmost.set(0, 0, FRACUNIT, -(32767 << FRACBITS));
 
 			secplane_t *topplane = i == 0 ? &topmost : &(*lightlist)[i].plane;
 			secplane_t *lowplane = i == (*lightlist).Size() - 1 ? &bottommost : &(*lightlist)[i + 1].plane;
diff --git a/src/gl/scene/gl_wall.h b/src/gl/scene/gl_wall.h
index 0069fe863..91567ecb5 100644
--- a/src/gl/scene/gl_wall.h
+++ b/src/gl/scene/gl_wall.h
@@ -86,7 +86,7 @@ struct GLSectorPlane
 		angle = sec->GetAngle(ceiling);
 		texture = sec->GetTexture(ceiling);
 		plane = sec->GetSecPlane(ceiling);
-		texheight = (ceiling == sector_t::ceiling)? plane.d : -plane.d;
+		texheight = (ceiling == sector_t::ceiling)? plane.fixD() : -plane.fixD();
 	}
 };
 
@@ -205,7 +205,7 @@ private:
 					  fixed_t fch1, fixed_t fch2, fixed_t ffh1, fixed_t ffh2,
 					  fixed_t bch1, fixed_t bch2, fixed_t bfh1, fixed_t bfh2);
 
-	void GetPlanePos(F3DFloor::planeref *planeref, int &left, int &right);
+	void GetPlanePos(F3DFloor::planeref *planeref, fixed_t &left, fixed_t &right);
 
 	void BuildFFBlock(seg_t * seg, F3DFloor * rover,
 					  fixed_t ff_topleft, fixed_t ff_topright, 
diff --git a/src/gl/scene/gl_walls.cpp b/src/gl/scene/gl_walls.cpp
index fad482dda..28eb76777 100644
--- a/src/gl/scene/gl_walls.cpp
+++ b/src/gl/scene/gl_walls.cpp
@@ -191,7 +191,7 @@ void GLWall::PutPortal(int ptype)
 		break;
 
 	case PORTALTYPE_PLANEMIRROR:
-		if (GLPortal::PlaneMirrorMode * planemirror->c <=0)
+		if (GLPortal::PlaneMirrorMode * planemirror->fC() <=0)
 		{
 			//@sync-portal
 			planemirror=UniquePlaneMirrors.Get(planemirror);
@@ -283,7 +283,7 @@ void GLWall::SplitWall(sector_t * frontsector, bool translucent)
 			if (i<lightlist.Size()-1) 
 			{
 				secplane_t &p = lightlist[i+1].plane;
-				if (p.a | p.b)
+				if (p.isSlope())
 				{
 					maplightbottomleft = p.ZatPoint(glseg.x1,glseg.y1);
 					maplightbottomright= p.ZatPoint(glseg.x2,glseg.y2);
@@ -1101,20 +1101,20 @@ void GLWall::BuildFFBlock(seg_t * seg, F3DFloor * rover,
 //
 //==========================================================================
 
-__forceinline void GLWall::GetPlanePos(F3DFloor::planeref *planeref, int &left, int &right)
+__forceinline void GLWall::GetPlanePos(F3DFloor::planeref *planeref, fixed_t &left, fixed_t &right)
 {
-	if (planeref->plane->a | planeref->plane->b)
+	if (planeref->plane->isSlope())
 	{
 		left=planeref->plane->ZatPoint(vertexes[0]);
 		right=planeref->plane->ZatPoint(vertexes[1]);
 	}
 	else if(planeref->isceiling == sector_t::ceiling)
 	{
-		left = right = planeref->plane->d;
+		left = right = planeref->plane->fixD();
 	}
 	else
 	{
-		left = right = -planeref->plane->d;
+		left = right = -planeref->plane->fixD();
 	}
 }
 
@@ -1450,7 +1450,7 @@ void GLWall::Process(seg_t *seg, sector_t * frontsector, sector_t * backsector)
 	bottomplane = frontsector->floorplane;
 
 	// Save a little time (up to 0.3 ms per frame ;) )
-	if (frontsector->floorplane.a | frontsector->floorplane.b)
+	if (frontsector->floorplane.isSlope())
 	{
 		ffh1 = segfront->floorplane.ZatPoint(v1);
 		ffh2 = segfront->floorplane.ZatPoint(v2);
@@ -1459,11 +1459,11 @@ void GLWall::Process(seg_t *seg, sector_t * frontsector, sector_t * backsector)
 	}
 	else
 	{
-		ffh1 = ffh2 = -segfront->floorplane.d;
+		ffh1 = ffh2 = -segfront->floorplane.fixD();
 		zfloor[0] = zfloor[1] = FIXED2FLOAT(ffh2);
 	}
 
-	if (segfront->ceilingplane.a | segfront->ceilingplane.b)
+	if (segfront->ceilingplane.isSlope())
 	{
 		fch1 = segfront->ceilingplane.ZatPoint(v1);
 		fch2 = segfront->ceilingplane.ZatPoint(v2);
@@ -1472,7 +1472,7 @@ void GLWall::Process(seg_t *seg, sector_t * frontsector, sector_t * backsector)
 	}
 	else
 	{
-		fch1 = fch2 = segfront->ceilingplane.d;
+		fch1 = fch2 = segfront->ceilingplane.fixD();
 		zceil[0] = zceil[1] = FIXED2FLOAT(fch2);
 	}
 
@@ -1520,24 +1520,24 @@ void GLWall::Process(seg_t *seg, sector_t * frontsector, sector_t * backsector)
 		fixed_t bfh1;
 		fixed_t bfh2;
 
-		if (segback->floorplane.a | segback->floorplane.b)
+		if (segback->floorplane.isSlope())
 		{
 			bfh1 = segback->floorplane.ZatPoint(v1);
 			bfh2 = segback->floorplane.ZatPoint(v2);
 		}
 		else
 		{
-			bfh1 = bfh2 = -segback->floorplane.d;
+			bfh1 = bfh2 = -segback->floorplane.fixD();
 		}
 
-		if (segback->ceilingplane.a | segback->ceilingplane.b)
+		if (segback->ceilingplane.isSlope())
 		{
 			bch1 = segback->ceilingplane.ZatPoint(v1);
 			bch2 = segback->ceilingplane.ZatPoint(v2);
 		}
 		else
 		{
-			bch1 = bch2 = segback->ceilingplane.d;
+			bch1 = bch2 = segback->ceilingplane.fixD();
 		}
 
 		SkyTop(seg, frontsector, backsector, v1, v2);
@@ -1568,8 +1568,7 @@ void GLWall::Process(seg_t *seg, sector_t * frontsector, sector_t * backsector)
 				}
 				else if (!(seg->sidedef->Flags & WALLF_POLYOBJ))
 				{
-					if ((frontsector->ceilingplane.a | frontsector->ceilingplane.b |
-						backsector->ceilingplane.a | backsector->ceilingplane.b) &&
+					if ((frontsector->ceilingplane.isSlope() || backsector->ceilingplane.isSlope()) &&
 						frontsector->GetTexture(sector_t::ceiling) != skyflatnum &&
 						backsector->GetTexture(sector_t::ceiling) != skyflatnum)
 					{
@@ -1649,8 +1648,7 @@ void GLWall::Process(seg_t *seg, sector_t * frontsector, sector_t * backsector)
 			}
 			else if (!(seg->sidedef->Flags & WALLF_POLYOBJ))
 			{
-				if ((frontsector->floorplane.a | frontsector->floorplane.b |
-					backsector->floorplane.a | backsector->floorplane.b) &&
+				if ((frontsector->ceilingplane.isSlope() || backsector->ceilingplane.isSlope()) &&
 					frontsector->GetTexture(sector_t::floor) != skyflatnum &&
 					backsector->GetTexture(sector_t::floor) != skyflatnum)
 				{
diff --git a/src/gl/utility/gl_geometric.cpp b/src/gl/utility/gl_geometric.cpp
index 5e3f93ba8..ef9bc88d4 100644
--- a/src/gl/utility/gl_geometric.cpp
+++ b/src/gl/utility/gl_geometric.cpp
@@ -229,10 +229,10 @@ void Plane::Set(secplane_t &plane)
 {
    float a, b, c, d;
 
-   a = FIXED2FLOAT(plane.a);
-   b = FIXED2FLOAT(plane.b);
-   c = FIXED2FLOAT(plane.c);
-   d = FIXED2FLOAT(plane.d);
+   a = (float)plane.fA();
+   b = (float)plane.fB();
+   c = (float)plane.fC();
+   d = (float)plane.fD();
 
    m_normal.Set(a, c, b);
    //m_normal.Normalize(); the vector is already normalized