Blob Maintenance: Stairs are Hard (#9146)

* Fix: Blobs respect gravity if not otherwise prevented.
Tweak: Blobs do not directly interact with stairs
Tweak: Blobs, when expanding against a stair's middle structure, can grow up Z-levels if the turf allows.
Tweak: Blobs, if controlled by a player, may grow upward or downward, if the turfs allow.
Fix: Blob Overmind is no longer affected by gravity.

* Fringe case deleted blobs are null-loc'd for GC so they are not stuck in-map.
Railing checks properly function.

code/game/objects/structures/railing.dm

@@ -64,6 +64,15 @@
 		new /obj/item/stack/rods(get_turf(src))
 		qdel(src)
 
+/obj/structure/railing/blob_act(var/obj/structure/blob/B)
+	. = ..()
+
+	if(B?.overmind?.blob_type)
+		take_damage(rand(B.overmind.blob_type.damage_lower, B.overmind.blob_type.damage_upper))
+		return
+
+	take_damage(rand(10,30))
+
 /obj/structure/railing/proc/NeighborsCheck(var/UpdateNeighbors = 1)
 	check = 0
 	//if (!anchored) return

code/modules/blob2/blobs/base_blob.dm

@@ -86,6 +86,10 @@ GLOBAL_LIST_EMPTY(all_blobs)
 		overmind.blob_type.on_emp(src, severity)
 
 /obj/structure/blob/proc/pulsed()
+	if(QDELETED(src))
+		loc = null
+		overmind = null
+		return
 	if(pulse_timestamp <= world.time)
 		consume_tile()
 		if(heal_timestamp <= world.time)
@@ -96,6 +100,7 @@ GLOBAL_LIST_EMPTY(all_blobs)
 		if(overmind)
 			faction = overmind.blob_type.faction
 			overmind.blob_type.on_pulse(src)
+		fall()	// Make sure to obey gravity.
 		return TRUE //we did it, we were pulsed!
 	return FALSE //oh no we failed
 
@@ -169,6 +174,11 @@ GLOBAL_LIST_EMPTY(all_blobs)
 		make_blob = FALSE
 		T.blob_act(src) //hit the turf if it is
 
+	if((locate(/obj/structure/stairs/middle) in T) && (locate(/obj/structure/stairs/bottom) in get_turf(src)))	// If we're growing against stairs, check for an open space above to grow 'up' the stairs.
+		var/turf/TAbove = GetAbove(src)
+		if(TAbove.CanZPass(src, UP))	// Can we pass through the turf above us to enter the tile? If so, swap T to that, we're going upstairs.
+			T = TAbove
+
 	for(var/atom/A in T)
 		if(!A.CanPass(src, T)) //is anything in the turf impassable
 			make_blob = FALSE
@@ -192,6 +202,21 @@ GLOBAL_LIST_EMPTY(all_blobs)
 	else
 		blob_attack_animation(T, controller) //if we can't, animate that we attacked
 
+/obj/structure/blob/fall_impact(var/atom/hit_atom, var/damage_min = 0, var/damage_max = 10, var/silent = FALSE, var/planetary = FALSE)
+	..()
+	playsound(src, 'sound/effects/splat.ogg', 50, 1)
+	consume_tile()
+
+/obj/structure/blob/can_fall()	// Despite popular belief, the blob's belief in its ability to fly doesn't matter. (Unless something else is holding it up)
+	if(overmind)
+		for(var/direction in cardinal)
+			var/turf/other_T = get_step(get_turf(src), direction)
+			if(other_T)
+				var/obj/structure/blob/B = locate(/obj/structure/blob/shield) in other_T
+				if(B && B.overmind)
+					return FALSE
+	return TRUE
+
 /obj/structure/blob/proc/do_slide_animation(var/obj/structure/blob/B, var/turf/T, var/expand_reaction)
 	set waitfor = FALSE
 	sleep(1) // To have the slide animation work.
@@ -201,6 +226,9 @@ GLOBAL_LIST_EMPTY(all_blobs)
 	B.density = initial(B.density)
 	B.forceMove(T)
 	B.update_icon()
+
+	B.fall()
+
 	if(B.overmind && expand_reaction)
 		B.overmind.blob_type.on_expand(src, B, T, B.overmind)
 
@@ -417,6 +445,7 @@ GLOBAL_LIST_EMPTY(all_blobs)
 		qdel(src)
 	else
 		update_icon()
+		fall()
 
 /obj/effect/temporary_effect/blob_attack
 	name = "blob"

code/modules/blob2/blobs/core.dm

@@ -144,7 +144,7 @@ var/global/list/blob_cores = list()
 //		overmind.update_health_hud()
 	pulse_area(overmind, 15, BLOB_CORE_PULSE_RANGE, BLOB_CORE_EXPAND_RANGE)
 	for(var/obj/structure/blob/normal/B in range(1, src))
-		if(prob(5))
+		if(B.overmind == overmind && prob(5))
 			B.change_to(/obj/structure/blob/shield/core, overmind)
 
 	overmind.blob_type.on_core_process(src)

code/modules/blob2/overmind/overmind.dm

@@ -62,6 +62,7 @@ var/global/list/overminds = list()
 		if(B && B.overmind == src)
 			B.overmind = null
 			B.update_icon() //reset anything that was ours
+			B.fall()	// No longer held up by whatever blob horror the core had going on (if any), fall like a really gross rock.
 
 	for(var/BLO in blob_mobs)
 		var/mob/living/simple_mob/blob/spore/BM = BLO
@@ -165,3 +166,6 @@ var/global/list/overminds = list()
 
 	log_say(message, src)
 	return 1
+
+/mob/observer/blob/can_fall()
+	return FALSE

code/modules/blob2/overmind/powers.dm

@@ -199,8 +199,24 @@
 			if(B && B.overmind == src)
 				break
 
+	// Only player-blobs can currently move up or down at will. AI-blobs can only fall downward.
+	if(!B)	// No cardinals, check if it can creep down from above or build up from below.
+		var/list/T_ZChecks = list()
+
+		T_ZChecks["UP"] = GetAbove(T)
+		T_ZChecks["DOWN"]= GetBelow(T)
+
+		for(var/zdir in T_ZChecks)
+			var/turf/T_check = T_ZChecks[zdir]
+			if(!T_check)
+				continue
+			B = locate(/obj/structure/blob) in T_check
+			if(B && T.CanZPass(B, (zdir == "UP") ? DOWN : UP))	// Can the blob [B] from [zdir] pass into the target turf by moving in the opposite direction. IE, A blob above enter by moving downward, or reverse.
+				break
+			B = null	// If both checks fail, B must be nulled for the next check.
+
 	if(!B)
-		to_chat(src, "<span class='warning'>There is no blob cardinally adjacent to the target tile!</span>")
+		to_chat(src, "<span class='warning'>There is no blob cardinally or vertically adjacent to the target tile!</span>")
 		return
 
 	if(!can_buy(4))

code/modules/multiz/stairs.dm

@@ -161,6 +161,9 @@
 	if(AM.has_buckled_mobs()) // Similarly, the rider entering the turf will bring along whatever they're buckled to
 		return
 
+	if(istype(AM, /obj/structure/blob))	// Blobs can't go down stairs normally. They kind of.. roll down them, when spreading. (See: They just fall.)
+		return
+
 	var/list/atom/movable/pulling = list() // Will also include grabbed mobs
 	if(isliving(AM))
 		var/mob/living/L = AM
@@ -203,6 +206,9 @@
 	if(isobserver(AM)) // Ghosts have their own methods for going up and down
 		return
 
+	if(istype(AM, /obj/structure/blob))	// Blobs can't go down stairs normally. They kind of.. roll down them, when spreading. (See: They just fall.)
+		return
+
 	if(isliving(AM))
 		var/mob/living/L = AM
 
@@ -417,6 +423,9 @@
 	if(AM.has_buckled_mobs()) // Similarly, the rider entering the turf will bring along whatever they're buckled to
 		return
 
+	if(istype(AM, /obj/structure/blob))	// Blobs can't go down stairs normally. They kind of.. roll down them, when spreading. (See: They just fall.)
+		return
+
 	var/list/atom/movable/pulling = list() // Will also include grabbed mobs
 	if(isliving(AM))
 		var/mob/living/L = AM
@@ -457,6 +466,9 @@
 	if(isobserver(AM)) // Ghosts have their own methods for going up and down
 		return
 
+	if(istype(AM, /obj/structure/blob))	// Blobs can't go down stairs normally. They kind of.. roll down them, when spreading. (See: They just fall.)
+		return
+
 	if(isliving(AM))
 		var/mob/living/L = AM