Add RF_HIDEINSKYBOX, stop rendering object in skybox

src/deh_tables.c

@@ -6196,6 +6196,7 @@ struct int_const_s const INT_CONST[] = {
 	{"RF_SHADOWEFFECTS",RF_SHADOWEFFECTS},
 	{"RF_DROPSHADOW",RF_DROPSHADOW},
 	{"RF_ABSOLUTELIGHTLEVEL",RF_ABSOLUTELIGHTLEVEL},
+	{"RF_HIDEINSKYBOX",RF_HIDEINSKYBOX},
 	{"RF_DONTDRAW",RF_DONTDRAW},
 	{"RF_DONTDRAWP1",RF_DONTDRAWP1},
 	{"RF_DONTDRAWP2",RF_DONTDRAWP2},

src/r_defs.h

@@ -944,6 +944,7 @@ typedef enum
 	RF_DROPSHADOW       = (RF_SHADOWDRAW | RF_SHADOWEFFECTS | RF_FULLDARK),
 
 	RF_ABSOLUTELIGHTLEVEL = 0x00010000, //  mobj_t.lightlevel is absolute instead of relative
+	RF_HIDEINSKYBOX       = 0x00020000, //  do not render in skybox
 
 	RF_DONTDRAW         = 0x00F00000,   // --Don't generate a vissprite
 	RF_DONTDRAWP1       = 0x00100000,   // No P1

src/r_things.c

@@ -2660,6 +2660,12 @@ void R_AddSprites(sector_t *sec, INT32 lightlevel)
 	limit_dist = (fixed_t)(cv_drawdist.value) * mapobjectscale;
 	for (thing = sec->thinglist; thing; thing = thing->snext)
 	{
+		// do not render in skybox
+		if ((thing->renderflags & RF_HIDEINSKYBOX) /*&& portalskipprecipmobjs*/)
+		{
+			continue;
+		}
+
 		if (R_ThingWithinDist(thing, limit_dist))
 		{
 			const INT32 oldobjectsdrawn = objectsdrawn;