Add more ways to prevent GZDoom from drawing skybox walls

Add noskywalls flag to sectors and linedefs

# Conflicts:
#	src/hwrenderer/scene/hw_sky.cpp
#	src/p_udmf.cpp

specs/udmf_zdoom.txt

@@ -140,6 +140,7 @@ Note: All <bool> fields default to false unless mentioned otherwise.
                                   // 12: Unexplored secret wall.
                                   // 13: Portal line.
       revealed = <bool>;          // true = line is initially visible on automap.
+      noskywalls = <bool>;        // true = skies are not drawn above or below this line
 
       health = <int>;             // Amount of hitpoints for this line.
       healthgroup = <int>;        // ID of destructible object to synchronize hitpoints (optional, default is 0)
@@ -285,6 +286,8 @@ Note: All <bool> fields default to false unless mentioned otherwise.
       coloradd_sprites = <int>;       // Additive material color applied to sprites within the sector. Default is black (0x000000)
       coloradd_walls = <int>;          // Additive material color applied to walls within the sector. Default is black (0x000000)
 
+      noskywalls = <bool>;            // If true, do not draw skybox walls above/below this sector
+
       portal_ceil_blocksound = <bool>;     // ceiling portal blocks sound.
       portal_ceil_disabled = <bool>;       // ceiling portal disabled.
       portal_ceil_nopass = <bool>;         // ceiling portal blocks movement if true.

src/doomdata.h

@@ -171,7 +171,7 @@ enum ELineFlags : unsigned
 	ML_BLOCKHITSCAN				= 0x08000000,	// blocks hitscan attacks
 	ML_3DMIDTEX_IMPASS			= 0x10000000,	// [TP] if 3D midtex, behaves like a height-restricted ML_BLOCKING
 	ML_REVEALED					= 0x20000000,	// set if revealed in automap
-
+	ML_NOSKYWALLS				= 0x40000000,	// Don't draw sky above or below walls
 	ML_PORTALCONNECT			= 0x80000000,	// for internal use only: This line connects to a sector with a linked portal (used to speed up sight checks.)
 };
 

src/gl/scene/gl_sky.cpp

@@ -232,8 +232,8 @@ void GLWall::SkyTop(seg_t * seg,sector_t * fs,sector_t * bs,vertex_t * v1,vertex
 {
 	if (fs->GetTexture(sector_t::ceiling)==skyflatnum)
 	{
-		if (bs->special == GLSector_NoSkyDraw) return;
-		if (bs->GetTexture(sector_t::ceiling)==skyflatnum) 
+		if (bs->special == GLSector_NoSkyDraw || bs->MoreFlags & SECMF_NOSKYWALLS || seg->linedef->flags & ML_NOSKYWALLS) return;
+		if (bs->GetTexture(sector_t::ceiling)==skyflatnum)
 		{
 			// if the back sector is closed the sky must be drawn!
 			if (bs->ceilingplane.ZatPoint(v1) > bs->floorplane.ZatPoint(v1) ||
@@ -326,7 +326,7 @@ void GLWall::SkyBottom(seg_t * seg,sector_t * fs,sector_t * bs,vertex_t * v1,ver
 {
 	if (fs->GetTexture(sector_t::floor)==skyflatnum)
 	{
-		if (bs->special == GLSector_NoSkyDraw) return;
+		if (bs->special == GLSector_NoSkyDraw || bs->MoreFlags & SECMF_NOSKYWALLS || seg->linedef->flags & ML_NOSKYWALLS) return;
 		FTexture * tex = TexMan(seg->sidedef->GetTexture(side_t::bottom));
 		
 		// For lower skies the normal logic only applies to walls with no lower texture!

src/namedef.h

@@ -592,6 +592,7 @@ xx(ColorAdd_Floor)
 xx(ColorAdd_Ceiling)
 xx(ColorAdd_Sprites)
 xx(ColorAdd_Walls)
+xx(NoSkyWalls)
 xx(Desaturation)
 xx(SoundSequence)
 xx(Silent)

src/p_udmf.cpp

@@ -1098,6 +1098,10 @@ public:
 				ld->automapstyle = AutomapLineStyle(CheckInt(key));
 				continue;
 
+			case NAME_NoSkyWalls:
+				Flag(ld->flags, ML_NOSKYWALLS, key);
+				continue;
+
 			case NAME_MoreIds:
 				// delay parsing of the tag string until parsing of the sector is complete
 				// This ensures that the ID is always the first tag in the list.
@@ -1664,6 +1668,10 @@ public:
 					sec->AdditiveColors[sector_t::sprites] = CheckInt(key) | 0xff000000;
 					break;
 
+				case NAME_NoSkyWalls:
+					Flag(sec->MoreFlags, SECMF_NOSKYWALLS, key);
+					break;
+
 				case NAME_Desaturation:
 					desaturation = int(255*CheckFloat(key) + FLT_EPSILON);	// FLT_EPSILON to avoid rounding errors with numbers slightly below a full integer.
 					continue;

src/r_defs.h

@@ -484,6 +484,7 @@ enum
 	SECMF_DRAWN				= 128,	// sector has been drawn at least once
 	SECMF_HIDDEN			= 256,	// Do not draw on textured automap
 	SECMF_OVERLAPPING		= 512,	// floor and ceiling overlap and require special renderer action.
+	SECMF_NOSKYWALLS		= 1024,	// Do not draw "sky walls"
 };
 
 enum