diff --git a/src/hardware/hw_main.c b/src/hardware/hw_main.c
index 8863de93..6a08b1c7 100644
--- a/src/hardware/hw_main.c
+++ b/src/hardware/hw_main.c
@@ -1319,7 +1319,7 @@ static void HWR_SplitWall(sector_t *sector, wallVert3D *wallVerts, INT32 texnum,
 
 // HWR_DrawSkyWalls
 // Draw walls into the depth buffer so that anything behind is culled properly
-static void HWR_DrawSkyWall(wallVert3D *wallVerts, FSurfaceInfo *Surf, fixed_t bottom, fixed_t top)
+static void HWR_DrawSkyWall(wallVert3D *wallVerts, FSurfaceInfo *Surf)
 {
 	HWD.pfnSetTexture(NULL);
 	// no texture
@@ -1327,9 +1327,6 @@ static void HWR_DrawSkyWall(wallVert3D *wallVerts, FSurfaceInfo *Surf, fixed_t b
 	wallVerts[0].t = wallVerts[1].t = 0;
 	wallVerts[0].s = wallVerts[3].s = 0;
 	wallVerts[2].s = wallVerts[1].s = 0;
-	// set top/bottom coords
-	wallVerts[2].y = wallVerts[3].y = FIXED_TO_FLOAT(top); // No real way to find the correct height of this
-	wallVerts[0].y = wallVerts[1].y = FIXED_TO_FLOAT(bottom); // worldlow/bottom because it needs to cover up the lower thok barrier wall
 	HWR_ProjectWall(wallVerts, Surf, PF_Invisible|PF_Clip|PF_NoTexture, 255, NULL);
 	// PF_Invisible so it's not drawn into the colour buffer
 	// PF_NoTexture for no texture
@@ -1462,6 +1459,111 @@ static void HWR_StoreWallRange(double startfrac, double endfrac)
 		worldlow  = gr_backsector->floorheight;
 #endif
 
+		// Sky culling
+		if (!gr_curline->polyseg) // Don't do it for polyobjects
+		{
+			// Sky Ceilings
+			wallVerts[3].y = wallVerts[2].y = FIXED_TO_FLOAT(INT32_MAX);
+
+			if (gr_frontsector->ceilingpic == skyflatnum)
+			{
+				if (gr_backsector->ceilingpic == skyflatnum)
+				{
+					// Both front and back sectors are sky, needs skywall from the frontsector's ceiling, but only if the
+					// backsector is lower
+					if ((worldhigh <= worldtop)
+#ifdef ESLOPE
+					&& (worldhighslope <= worldtopslope)
+#endif
+					)
+					{
+#ifdef ESLOPE
+						wallVerts[0].y = FIXED_TO_FLOAT(worldhigh);
+						wallVerts[1].y = FIXED_TO_FLOAT(worldhighslope);
+#else
+						wallVerts[0].y = wallVerts[1].y = FIXED_TO_FLOAT(worldhigh);
+#endif
+						HWR_DrawSkyWall(wallVerts, &Surf);
+					}
+				}
+				else
+				{
+					// Only the frontsector is sky, just draw a skywall from the front ceiling
+#ifdef ESLOPE
+					wallVerts[0].y = FIXED_TO_FLOAT(worldtop);
+					wallVerts[1].y = FIXED_TO_FLOAT(worldtopslope);
+#else
+					wallVerts[0].y = wallVerts[1].y = FIXED_TO_FLOAT(worldtop);
+#endif
+					HWR_DrawSkyWall(wallVerts, &Surf);
+				}
+			}
+			else if (gr_backsector->ceilingpic == skyflatnum)
+			{
+				// Only the backsector is sky, just draw a skywall from the front ceiling
+#ifdef ESLOPE
+				wallVerts[0].y = FIXED_TO_FLOAT(worldtop);
+				wallVerts[1].y = FIXED_TO_FLOAT(worldtopslope);
+#else
+				wallVerts[0].y = wallVerts[1].y = FIXED_TO_FLOAT(worldtop);
+#endif
+				HWR_DrawSkyWall(wallVerts, &Surf);
+			}
+
+
+			// Sky Floors
+			wallVerts[0].y = wallVerts[1].y = FIXED_TO_FLOAT(INT32_MIN);
+
+			if (gr_frontsector->floorpic == skyflatnum)
+			{
+				if (gr_backsector->floorpic == skyflatnum)
+				{
+					// Both front and back sectors are sky, needs skywall from the backsector's floor, but only if the
+					// it's higher, also needs to check for bottomtexture as the floors don't usually move down
+					// when both sides are sky floors
+					if ((worldlow >= worldbottom)
+#ifdef ESLOPE
+					&& (worldlowslope >= worldbottomslope)
+#endif
+					&& !(gr_sidedef->bottomtexture))
+					{
+#ifdef ESLOPE
+						wallVerts[3].y = FIXED_TO_FLOAT(worldlow);
+						wallVerts[2].y = FIXED_TO_FLOAT(worldlowslope);
+#else
+						wallVerts[3].y = wallVerts[2].y = FIXED_TO_FLOAT(worldlow);
+#endif
+
+						HWR_DrawSkyWall(wallVerts, &Surf);
+					}
+				}
+				else
+				{
+					// Only the backsector has sky, just draw a skywall from the back floor
+#ifdef ESLOPE
+					wallVerts[3].y = FIXED_TO_FLOAT(worldbottom);
+					wallVerts[2].y = FIXED_TO_FLOAT(worldbottomslope);
+#else
+					wallVerts[3].y = wallVerts[2].y = FIXED_TO_FLOAT(worldbottom);
+#endif
+
+					HWR_DrawSkyWall(wallVerts, &Surf);
+				}
+			}
+			else if ((gr_backsector->floorpic == skyflatnum) && !(gr_sidedef->bottomtexture))
+			{
+				// Only the backsector has sky, just draw a skywall from the back floor if there's no bottomtexture
+#ifdef ESLOPE
+				wallVerts[3].y = FIXED_TO_FLOAT(worldlow);
+				wallVerts[2].y = FIXED_TO_FLOAT(worldlowslope);
+#else
+				wallVerts[3].y = wallVerts[2].y = FIXED_TO_FLOAT(worldlow);
+#endif
+
+				HWR_DrawSkyWall(wallVerts, &Surf);
+			}
+		}
+
 		// hack to allow height changes in outdoor areas
 		// This is what gets rid of the upper textures if there should be sky
 		if (gr_frontsector->ceilingpic == skyflatnum &&
@@ -1914,85 +2016,6 @@ static void HWR_StoreWallRange(double startfrac, double endfrac)
 				Surf.FlatColor.rgba = 0xffffffff;
 			}*/
 		}
-
-		// Isn't this just the most lovely mess
-		if (!gr_curline->polyseg) // Don't do it for polyobjects
-		{
-			if (gr_frontsector->ceilingpic == skyflatnum || gr_backsector->ceilingpic == skyflatnum)
-			{
-				fixed_t depthwallheight;
-
-				if (!gr_sidedef->toptexture || (gr_frontsector->ceilingpic == skyflatnum && gr_backsector->ceilingpic == skyflatnum)) // when both sectors are sky, the top texture isn't drawn
-					depthwallheight = gr_frontsector->ceilingheight < gr_backsector->ceilingheight ? gr_frontsector->ceilingheight : gr_backsector->ceilingheight;
-				else
-					depthwallheight = gr_frontsector->ceilingheight > gr_backsector->ceilingheight ? gr_frontsector->ceilingheight : gr_backsector->ceilingheight;
-
-				if (gr_frontsector->ceilingheight-gr_frontsector->floorheight <= 0) // current sector is a thok barrier
-				{
-					if (gr_backsector->ceilingheight-gr_backsector->floorheight <= 0) // behind sector is also a thok barrier
-					{
-						if (!gr_sidedef->bottomtexture) // Only extend further down if there's no texture
-							HWR_DrawSkyWall(wallVerts, &Surf, worldbottom < worldlow ? worldbottom : worldlow, INT32_MAX);
-						else
-							HWR_DrawSkyWall(wallVerts, &Surf, worldbottom > worldlow ? worldbottom : worldlow, INT32_MAX);
-					}
-					// behind sector is not a thok barrier
-					else if (gr_backsector->ceilingheight <= gr_frontsector->ceilingheight) // behind sector ceiling is lower or equal to current sector
-						HWR_DrawSkyWall(wallVerts, &Surf, depthwallheight, INT32_MAX);
-						// gr_front/backsector heights need to be used here because of the worldtop being set to worldhigh earlier on
-				}
-				else if (gr_backsector->ceilingheight-gr_backsector->floorheight <= 0) // behind sector is a thok barrier, current sector is not
-				{
-					if (gr_backsector->ceilingheight >= gr_frontsector->ceilingheight // thok barrier ceiling height is equal to or greater than current sector ceiling height
-						|| gr_backsector->floorheight <= gr_frontsector->floorheight // thok barrier ceiling height is equal to or less than current sector floor height
-						|| gr_backsector->ceilingpic != skyflatnum) // thok barrier is not a sky
-						HWR_DrawSkyWall(wallVerts, &Surf, depthwallheight, INT32_MAX);
-				}
-				else // neither sectors are thok barriers
-				{
-					if ((gr_backsector->ceilingheight < gr_frontsector->ceilingheight && !gr_sidedef->toptexture) // no top texture and sector behind is lower
-						|| gr_backsector->ceilingpic != skyflatnum) // behind sector is not a sky
-						HWR_DrawSkyWall(wallVerts, &Surf, depthwallheight, INT32_MAX);
-				}
-			}
-			// And now for sky floors!
-			if (gr_frontsector->floorpic == skyflatnum || gr_backsector->floorpic == skyflatnum)
-			{
-				fixed_t depthwallheight;
-
-				if (!gr_sidedef->bottomtexture)
-					depthwallheight = worldbottom > worldlow ? worldbottom : worldlow;
-				else
-					depthwallheight = worldbottom < worldlow ? worldbottom : worldlow;
-
-				if (gr_frontsector->ceilingheight-gr_frontsector->floorheight <= 0) // current sector is a thok barrier
-				{
-					if (gr_backsector->ceilingheight-gr_backsector->floorheight <= 0) // behind sector is also a thok barrier
-					{
-						if (!gr_sidedef->toptexture) // Only extend up if there's no texture
-							HWR_DrawSkyWall(wallVerts, &Surf, INT32_MIN, worldtop > worldhigh ? worldtop : worldhigh);
-						else
-							HWR_DrawSkyWall(wallVerts, &Surf, INT32_MIN, worldtop < worldhigh ? worldtop : worldhigh);
-					}
-					// behind sector is not a thok barrier
-					else if (gr_backsector->floorheight >= gr_frontsector->floorheight) // behind sector floor is greater or equal to current sector
-						HWR_DrawSkyWall(wallVerts, &Surf, INT32_MIN, depthwallheight);
-				}
-				else if (gr_backsector->ceilingheight-gr_backsector->floorheight <= 0) // behind sector is a thok barrier, current sector is not
-				{
-					if (gr_backsector->floorheight <= gr_frontsector->floorheight // thok barrier floor height is equal to or less than current sector floor height
-						|| gr_backsector->ceilingheight >= gr_frontsector->ceilingheight // thok barrier floor height is equal to or greater than current sector ceiling height
-						|| gr_backsector->floorpic != skyflatnum) // thok barrier is not a sky
-						HWR_DrawSkyWall(wallVerts, &Surf, INT32_MIN, depthwallheight);
-				}
-				else // neither sectors are thok barriers
-				{
-					if ((gr_backsector->floorheight > gr_frontsector->floorheight && !gr_sidedef->bottomtexture) // no bottom texture and sector behind is higher
-						|| gr_backsector->floorpic != skyflatnum) // behind sector is not a sky
-						HWR_DrawSkyWall(wallVerts, &Surf, INT32_MIN, depthwallheight);
-				}
-			}
-		}
 	}
 	else
 	{
@@ -2060,13 +2083,52 @@ static void HWR_StoreWallRange(double startfrac, double endfrac)
 					HWR_ProjectWall(wallVerts, &Surf, PF_Masked, lightnum, colormap);
 			}
 		}
+		else
+		{
+#ifdef ESLOPE
+			//Set textures properly on single sided walls that are sloped
+			wallVerts[3].y = FIXED_TO_FLOAT(worldtop);
+			wallVerts[0].y = FIXED_TO_FLOAT(worldbottom);
+			wallVerts[2].y = FIXED_TO_FLOAT(worldtopslope);
+			wallVerts[1].y = FIXED_TO_FLOAT(worldbottomslope);
+#else
+			// set top/bottom coords
+			wallVerts[2].y = wallVerts[3].y = FIXED_TO_FLOAT(worldtop);
+			wallVerts[0].y = wallVerts[1].y = FIXED_TO_FLOAT(worldbottom);
+#endif
 
+			// When there's no midtexture, draw a skywall to prevent rendering behind it
+			HWR_DrawSkyWall(wallVerts, &Surf);
+		}
+
+
+		// Single sided lines are simple for skywalls, just need to draw from the top or bottom of the sector if there's
+		// a sky flat
 		if (!gr_curline->polyseg)
 		{
 			if (gr_frontsector->ceilingpic == skyflatnum) // It's a single-sided line with sky for its sector
-				HWR_DrawSkyWall(wallVerts, &Surf, worldtop, INT32_MAX);
+			{
+				wallVerts[3].y = wallVerts[2].y = FIXED_TO_FLOAT(INT32_MAX);
+#ifdef ESLOPE
+				wallVerts[0].y = FIXED_TO_FLOAT(worldtop);
+				wallVerts[1].y = FIXED_TO_FLOAT(worldtopslope);
+#else
+				wallVerts[0].y = wallVerts[1].y = FIXED_TO_FLOAT(worldtop);
+#endif
+				HWR_DrawSkyWall(wallVerts, &Surf);
+			}
 			if (gr_frontsector->floorpic == skyflatnum)
-				HWR_DrawSkyWall(wallVerts, &Surf, INT32_MIN, worldbottom);
+			{
+#ifdef ESLOPE
+				wallVerts[3].y = FIXED_TO_FLOAT(worldbottom);
+				wallVerts[2].y = FIXED_TO_FLOAT(worldbottomslope);
+#else
+				wallVerts[3].y = wallVerts[2].y = FIXED_TO_FLOAT(worldbottom);
+#endif
+				wallVerts[0].y = wallVerts[1].y = FIXED_TO_FLOAT(INT32_MIN);
+
+				HWR_DrawSkyWall(wallVerts, &Surf);
+			}
 		}
 	}
 
@@ -2381,7 +2443,7 @@ static void HWR_StoreWallRange(double startfrac, double endfrac)
 // e6y: Check whether the player can look beyond this line
 //
 #ifdef NEWCLIP
-boolean checkforemptylines = true;
+static boolean checkforemptylines = true;
 // Don't modify anything here, just check
 // Kalaron: Modified for sloped linedefs
 static boolean CheckClip(seg_t * seg, sector_t * afrontsector, sector_t * abacksector)
@@ -2421,62 +2483,47 @@ static boolean CheckClip(seg_t * seg, sector_t * afrontsector, sector_t * abacks
 		backc1 = backc2 = abacksector->ceilingheight;
 	}
 
-	// now check for closed sectors!
-	if (backc1 <= frontf1 && backc2 <= frontf2)
+	if (viewsector != abacksector && viewsector != afrontsector)
 	{
-		checkforemptylines = false;
-		if (!seg->sidedef->toptexture)
-			return false;
+		boolean mydoorclosed = false; // My door? Closed!? (doorclosed is actually otherwise unused in openGL)
 
-		if (abacksector->ceilingpic == skyflatnum && afrontsector->ceilingpic == skyflatnum)
-			return false;
-
-		return true;
-	}
-
-	if (backf1 >= frontc1 && backf2 >= frontc2)
-	{
-		checkforemptylines = false;
-		if (!seg->sidedef->bottomtexture)
-			return false;
-
-		// properly render skies (consider door "open" if both floors are sky):
-		if (abacksector->ceilingpic == skyflatnum && afrontsector->ceilingpic == skyflatnum)
-			return false;
-
-		return true;
-	}
-
-	if (backc1 <= backf1 && backc2 <= backf2)
-	{
-		checkforemptylines = false;
-		// preserve a kind of transparent door/lift special effect:
-		if (backc1 < frontc1 || backc2 < frontc2)
-		{
-			if (!seg->sidedef->toptexture)
-				return false;
-		}
-		if (backf1 > frontf1 || backf2 > frontf2)
-		{
-			if (!seg->sidedef->bottomtexture)
-				return false;
-		}
-		if (abacksector->ceilingpic == skyflatnum && afrontsector->ceilingpic == skyflatnum)
-			return false;
-
-		if (abacksector->floorpic == skyflatnum && afrontsector->floorpic == skyflatnum)
-			return false;
-
-		return true;
-	}
-
-	if (backc1 != frontc1 || backc2 != frontc2
-		|| backf1 != frontf1 || backf2 != frontf2)
+		// If the sector behind the line blocks all kinds of view past it
+		// (back ceiling is lower than close floor, or back floor is higher than close ceiling)
+		if ((backc1 <= frontf1 && backc2 <= frontf2)
+			|| (backf1 >= frontc1 && backf2 >= frontc2))
 		{
 			checkforemptylines = false;
-			return false;
+			return true;
 		}
 
+		// The door is closed if:
+		// backsector is 0 height or less and
+		// back ceiling is higher than close ceiling or we need to render a top texture and
+		// back floor is lower than close floor or we need to render a bottom texture and
+		// neither front or back sectors are using the sky ceiling
+		mydoorclosed = (backc1 <= backf1 && backc2 <= backf2
+		&& ((backc1 >= frontc1 && backc2 >= frontc2) || seg->sidedef->toptexture)
+		&& ((backf1 <= frontf1 && backf2 >= frontf2) || seg->sidedef->bottomtexture)
+		&& (abacksector->ceilingpic != skyflatnum || afrontsector->ceilingpic != skyflatnum));
+
+		if (mydoorclosed)
+		{
+			checkforemptylines = false;
+			return true;
+		}
+	}
+
+	// Window.
+	// We know it's a window when the above isn't true and the back and front sectors don't match
+	if (backc1 != frontc1 || backc2 != frontc2
+		|| backf1 != frontf1 || backf2 != frontf2)
+	{
+		checkforemptylines = false;
+		return false;
+	}
+
+	// In this case we just need to check whether there is actually a need to render any lines, so checkforempty lines
+	// stays true
 	return false;
 }
 #else