- added 'revealed on automap' linedef flag, UDMF only

https://forum.zdoom.org/viewtopic.php?t=59808
(cherry picked from commit 90cb0b3215)

src/am_map.cpp

@@ -2664,7 +2664,7 @@ void AM_drawWalls (bool allmap)
 					AM_drawMline(&l, AMColors.TSWallColor);
 				}
 			}
-			else if (allmap)
+			else if (allmap || (line.flags & ML_REVEALED))
 			{
 				if ((line.flags & ML_DONTDRAW) && (am_cheat == 0 || am_cheat >= 4))
 				{

src/doomdata.h

@@ -170,6 +170,7 @@ enum ELineFlags : unsigned
 	ML_BLOCKSIGHT				= 0x04000000,	// blocks monster line of sight
 	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_PORTALCONNECT			= 0x80000000,	// for internal use only: This line connects to a sector with a linked portal (used to speed up sight checks.)
 };

src/namedef.h

@@ -537,6 +537,7 @@ xx(Repeatspecial)
 xx(Conversation)
 xx(Locknumber)
 xx(Midtex3dimpassible)
+xx(Revealed)
 
 xx(Playercross)
 xx(Playeruse)

src/p_udmf.cpp

@@ -1110,6 +1110,10 @@ public:
 				Flag(ld->flags, ML_3DMIDTEX_IMPASS, key);
 				continue;
 
+			case NAME_Revealed:
+				Flag(ld->flags, ML_REVEALED, 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.