diff --git a/src/hardware/hw_main.c b/src/hardware/hw_main.c
index f253861de36dbd65d40a108728a0f2ce91c11338..bc66955fca4aab762076b4e322afe47ba548b2b2 100644
--- a/src/hardware/hw_main.c
+++ b/src/hardware/hw_main.c
@@ -1699,7 +1699,7 @@ static void HWR_ProcessSeg(void) // Sort of like GLWall::Process in GZDoom
 					if ((rover->fofflags & FOF_TRANSLUCENT && !(rover->fofflags & FOF_SPLAT)) || rover->blend)
 					{
 						blendmode = rover->blend ? HWR_GetBlendModeFlag(rover->blend) : PF_Translucent;
-						Surf.PolyColor.s.alpha = (UINT8)rover->alpha-1 > 255 ? 255 : rover->alpha-1;
+						Surf.PolyColor.s.alpha = max(0, min(rover->alpha, 255));
 					}
 
 					if (gl_frontsector->numlights)
@@ -1822,7 +1822,7 @@ static void HWR_ProcessSeg(void) // Sort of like GLWall::Process in GZDoom
 					if ((rover->fofflags & FOF_TRANSLUCENT && !(rover->fofflags & FOF_SPLAT)) || rover->blend)
 					{
 						blendmode = rover->blend ? HWR_GetBlendModeFlag(rover->blend) : PF_Translucent;
-						Surf.PolyColor.s.alpha = (UINT8)rover->alpha-1 > 255 ? 255 : rover->alpha-1;
+						Surf.PolyColor.s.alpha = max(0, min(rover->alpha, 255));
 					}
 
 					if (gl_backsector->numlights)
@@ -3095,7 +3095,7 @@ static void HWR_Subsector(size_t num)
 										   false,
 					                       *rover->bottomheight,
 					                       *gl_frontsector->lightlist[light].lightlevel,
-					                       rover->alpha-1 > 255 ? 255 : rover->alpha-1, rover->master->frontsector,
+					                       max(0, min(rover->alpha, 255)), rover->master->frontsector,
 					                       HWR_RippleBlend(gl_frontsector, rover, false) | (rover->blend ? HWR_GetBlendModeFlag(rover->blend) : PF_Translucent),
 					                       false, *gl_frontsector->lightlist[light].extra_colormap);
 				}
@@ -3141,7 +3141,7 @@ static void HWR_Subsector(size_t num)
 											true,
 					                        *rover->topheight,
 					                        *gl_frontsector->lightlist[light].lightlevel,
-					                        rover->alpha-1 > 255 ? 255 : rover->alpha-1, rover->master->frontsector,
+					                        max(0, min(rover->alpha, 255)), rover->master->frontsector,
 					                        HWR_RippleBlend(gl_frontsector, rover, false) | (rover->blend ? HWR_GetBlendModeFlag(rover->blend) : PF_Translucent),
 					                        false, *gl_frontsector->lightlist[light].extra_colormap);
 				}
diff --git a/src/p_spec.c b/src/p_spec.c
index 169f129b9589834bb1ecd44a98e8060d5eb49380..28ecc60f4dedb5f67f9aa33e092232eb0b3782f6 100644
--- a/src/p_spec.c
+++ b/src/p_spec.c
@@ -3286,19 +3286,18 @@ static void P_ProcessLineSpecial(line_t *line, mobj_t *mo, sector_t *callsec)
 						foundrover = true;
 
 						// If fading an invisible FOF whose render flags we did not yet set,
-						// initialize its alpha to 1
-						// for relative alpha calc
+						// initialize its alpha to 0 for relative alpha calculation
 						if (!(line->args[3] & TMST_DONTDOTRANSLUCENT) &&      // do translucent
 							(rover->spawnflags & FOF_NOSHADE) && // do not include light blocks, which don't set FOF_NOSHADE
 							!(rover->spawnflags & FOF_RENDERSIDES) &&
 							!(rover->spawnflags & FOF_RENDERPLANES) &&
 							!(rover->fofflags & FOF_RENDERALL))
-							rover->alpha = 1;
+							rover->alpha = 0;
 
 						P_RemoveFakeFloorFader(rover);
 						P_FadeFakeFloor(rover,
 							rover->alpha,
-							max(1, min(256, (line->args[3] & TMST_RELATIVE) ? rover->alpha + destvalue : destvalue)),
+							max(0, min(255, (line->args[3] & TMST_RELATIVE) ? rover->alpha + destvalue : destvalue)),
 							0,                                         // set alpha immediately
 							false, NULL,                               // tic-based logic
 							false,                                     // do not handle FOF_EXISTS
@@ -3372,19 +3371,18 @@ static void P_ProcessLineSpecial(line_t *line, mobj_t *mo, sector_t *callsec)
 						else
 						{
 							// If fading an invisible FOF whose render flags we did not yet set,
-							// initialize its alpha to 1
-							// for relative alpha calc
+							// initialize its alpha to 1 for relative alpha calculation
 							if (!(line->args[4] & TMFT_DONTDOTRANSLUCENT) &&      // do translucent
 								(rover->spawnflags & FOF_NOSHADE) && // do not include light blocks, which don't set FOF_NOSHADE
 								!(rover->spawnflags & FOF_RENDERSIDES) &&
 								!(rover->spawnflags & FOF_RENDERPLANES) &&
 								!(rover->fofflags & FOF_RENDERALL))
-								rover->alpha = 1;
+								rover->alpha = 0;
 
 							P_RemoveFakeFloorFader(rover);
 							P_FadeFakeFloor(rover,
 								rover->alpha,
-								max(1, min(256, (line->args[4] & TMFT_RELATIVE) ? rover->alpha + destvalue : destvalue)),
+								max(0, min(255, (line->args[4] & TMFT_RELATIVE) ? rover->alpha + destvalue : destvalue)),
 								0,                                         // set alpha immediately
 								false, NULL,                               // tic-based logic
 								!(line->args[4] & TMFT_DONTDOEXISTS),      // do not handle FOF_EXISTS
@@ -6565,10 +6563,10 @@ void P_SpawnSpecials(boolean fromnetsave)
 				//Cutting options
 				if (ffloorflags & FOF_RENDERALL)
 				{
-					//If inside is visible, cut inner walls
-					if ((lines[i].args[1] < 255) || (lines[i].args[3] & TMFA_SPLAT) || (lines[i].args[4] & TMFT_VISIBLEFROMINSIDE))
+					//If inside is visible from the outside, cut inner walls
+					if (lines[i].args[1] < 255 || (lines[i].args[3] & TMFA_SPLAT))
 						ffloorflags |= FOF_CUTEXTRA|FOF_EXTRA;
-					else
+					else if (!(lines[i].args[4] & TMFT_VISIBLEFROMINSIDE))
 						ffloorflags |= FOF_CUTLEVEL;
 				}
 
@@ -6624,20 +6622,19 @@ void P_SpawnSpecials(boolean fromnetsave)
 				if (lines[i].args[4] & TMFC_SPLAT)
 					ffloorflags |= FOF_SPLAT;
 
-				//If inside is visible, cut inner walls
-				if (lines[i].args[1] < 0xff || (lines[i].args[3] & TMFT_VISIBLEFROMINSIDE) || (lines[i].args[4] & TMFC_SPLAT))
+				//If inside is visible from the outside, cut inner walls
+				if (lines[i].args[1] < 255 || (lines[i].args[4] & TMFC_SPLAT))
 					ffloorflags |= FOF_CUTEXTRA|FOF_EXTRA;
-				else
-					ffloorflags |= FOF_CUTLEVEL;
-
-				//If player can enter it, render insides
-				if (lines[i].args[3] & TMFT_VISIBLEFROMINSIDE)
+				//If player can view it from the inside, render insides
+				else if (lines[i].args[3] & TMFT_VISIBLEFROMINSIDE)
 				{
 					if (ffloorflags & FOF_RENDERPLANES)
 						ffloorflags |= FOF_BOTHPLANES;
 					if (ffloorflags & FOF_RENDERSIDES)
 						ffloorflags |= FOF_ALLSIDES;
 				}
+				else
+					ffloorflags |= FOF_CUTLEVEL;
 
 				P_AddFakeFloorsByLine(i, lines[i].args[1], lines[i].args[2], ffloorflags, secthinkers);
 				if (lines[i].args[4] & TMFC_AIRBOB)
@@ -6688,10 +6685,10 @@ void P_SpawnSpecials(boolean fromnetsave)
 				//Cutting options
 				if (ffloorflags & FOF_RENDERALL)
 				{
-					//If inside is visible, cut inner walls
-					if ((lines[i].args[1] < 255) || (lines[i].args[3] & TMFA_SPLAT) || (lines[i].args[4] & TMFT_VISIBLEFROMINSIDE))
+					//If inside is visible from the outside, cut inner walls
+					if (lines[i].args[1] < 255 || (lines[i].args[3] & TMFA_SPLAT))
 						ffloorflags |= FOF_CUTEXTRA|FOF_EXTRA;
-					else
+					else if (!(lines[i].args[4] & TMFT_VISIBLEFROMINSIDE))
 						ffloorflags |= FOF_CUTLEVEL;
 				}
 
@@ -7756,15 +7753,14 @@ static boolean P_FadeFakeFloor(ffloor_t *rover, INT16 sourcevalue, INT16 destval
 	if (rover->master->special == 258) // Laser block
 		return false;
 
-	// If fading an invisible FOF whose render flags we did not yet set,
-	// initialize its alpha to 1
+	// If fading an invisible FOF whose render flags we did not yet set, initialize its alpha to 1
 	if (dotranslucent &&
 		(rover->spawnflags & FOF_NOSHADE) && // do not include light blocks, which don't set FOF_NOSHADE
 		!(rover->fofflags & FOF_FOG) && // do not include fog
 		!(rover->spawnflags & FOF_RENDERSIDES) &&
 		!(rover->spawnflags & FOF_RENDERPLANES) &&
 		!(rover->fofflags & FOF_RENDERALL))
-		rover->alpha = 1;
+		rover->alpha = 0;
 
 	if (fadingdata)
 		alpha = fadingdata->alpha;
@@ -7850,7 +7846,7 @@ static boolean P_FadeFakeFloor(ffloor_t *rover, INT16 sourcevalue, INT16 destval
 	{
 		if (doexists && !(rover->spawnflags & FOF_BUSTUP))
 		{
-			if (alpha <= 1)
+			if (alpha <= 0)
 				rover->fofflags &= ~FOF_EXISTS;
 			else
 				rover->fofflags |= FOF_EXISTS;
@@ -7862,7 +7858,7 @@ static boolean P_FadeFakeFloor(ffloor_t *rover, INT16 sourcevalue, INT16 destval
 
 		if (dotranslucent && !(rover->fofflags & FOF_FOG))
 		{
-			if (alpha >= 256)
+			if (alpha >= 255)
 			{
 				if (!(rover->fofflags & FOF_CUTSOLIDS) &&
 					(rover->spawnflags & FOF_CUTSOLIDS))
@@ -7962,11 +7958,11 @@ static boolean P_FadeFakeFloor(ffloor_t *rover, INT16 sourcevalue, INT16 destval
 		else // clamp fadingdata->alpha to software's alpha levels
 		{
 			if (alpha < 12)
-				rover->alpha = destvalue < 12 ? destvalue : 1; // Don't even draw it
+				rover->alpha = destvalue < 12 ? destvalue : 0; // Don't even draw it
 			else if (alpha < 38)
 				rover->alpha = destvalue >= 12 && destvalue < 38 ? destvalue : 25;
 			else if (alpha < 64)
-				rover->alpha = destvalue >=38 && destvalue < 64 ? destvalue : 51;
+				rover->alpha = destvalue >= 38 && destvalue < 64 ? destvalue : 51;
 			else if (alpha < 89)
 				rover->alpha = destvalue >= 64 && destvalue < 89 ? destvalue : 76;
 			else if (alpha < 115)
@@ -7982,7 +7978,7 @@ static boolean P_FadeFakeFloor(ffloor_t *rover, INT16 sourcevalue, INT16 destval
 			else if (alpha < 243)
 				rover->alpha = destvalue >= 217 && destvalue < 243 ? destvalue : 230;
 			else // Opaque
-				rover->alpha = destvalue >= 243 ? destvalue : 256;
+				rover->alpha = destvalue >= 243 ? destvalue : 255;
 		}
 	}
 
@@ -8012,17 +8008,16 @@ static void P_AddFakeFloorFader(ffloor_t *rover, size_t sectornum, size_t ffloor
 {
 	fade_t *d;
 
-	// If fading an invisible FOF whose render flags we did not yet set,
-	// initialize its alpha to 1
+	// If fading an invisible FOF whose render flags we did not yet set, initialize its alpha to 1
 	if (dotranslucent &&
 		(rover->spawnflags & FOF_NOSHADE) && // do not include light blocks, which don't set FOF_NOSHADE
 		!(rover->spawnflags & FOF_RENDERSIDES) &&
 		!(rover->spawnflags & FOF_RENDERPLANES) &&
 		!(rover->fofflags & FOF_RENDERALL))
-		rover->alpha = 1;
+		rover->alpha = 0;
 
 	// already equal, nothing to do
-	if (rover->alpha == max(1, min(256, relative ? rover->alpha + destvalue : destvalue)))
+	if (rover->alpha == max(0, min(255, relative ? rover->alpha + destvalue : destvalue)))
 		return;
 
 	d = Z_Malloc(sizeof *d, PU_LEVSPEC, NULL);
@@ -8033,7 +8028,7 @@ static void P_AddFakeFloorFader(ffloor_t *rover, size_t sectornum, size_t ffloor
 	d->ffloornum = (UINT32)ffloornum;
 
 	d->alpha = d->sourcevalue = rover->alpha;
-	d->destvalue = max(1, min(256, relative ? rover->alpha + destvalue : destvalue)); // rover->alpha is 1-256
+	d->destvalue = max(0, min(255, relative ? rover->alpha + destvalue : destvalue)); // rover->alpha is 0-255
 
 	if (ticbased)
 	{