Refactors the forceMove() drop.

Makes dropping a its proc instead, cleaning up forceMove() handling.

code/game/atoms.dm

@@ -463,11 +463,11 @@ its easier to just keep the beam vertical.
 			//spawn(0)
 			//if(I) //It's possible that it could be deleted in the meantime.
 			var/obj/O = I
-			O.show_message( message, 1, blind_message, 2)
+			O.show_message(message, 1, blind_message, 2)
 		else if(ismob(I))
 			var/mob/M = I
 			if(M.see_invisible >= invisibility) // Cannot view the invisible
-				M.show_message( message, 1, blind_message, 2)
+				M.show_message(message, 1, blind_message, 2)
 			else if (blind_message)
 				M.show_message(blind_message, 2)
 
@@ -488,7 +488,24 @@ its easier to just keep the beam vertical.
 			spawn(0)
 				if(I) //It's possible that it could be deleted in the meantime.
 					var/obj/O = I
-					O.show_message( message, 2, deaf_message, 1)
+					O.show_message(message, 2, deaf_message, 1)
 		else if(ismob(I))
 			var/mob/M = I
-			M.show_message( message, 2, deaf_message, 1)
+			M.show_message(message, 2, deaf_message, 1)
+
+/atom/movable/proc/dropInto(var/atom/destination)
+	while(istype(destination))
+		var/atom/drop_destination = destination.onDropInto(src)
+		if(!istype(drop_destination) || drop_destination == destination)
+			return forceMove(destination)
+		destination = drop_destination
+	return forceMove(null)
+
+/atom/proc/onDropInto(var/atom/movable/AM)
+	return // If onDropInto returns null, then dropInto will forceMove AM into us.
+
+/atom/movable/onDropInto(var/atom/movable/AM)
+	return loc // If onDropInto returns something, then dropInto will attempt to drop AM there.
+
+/atom/proc/InsertedContents()
+	return contents

code/game/atoms_movable.dm

@@ -63,13 +63,35 @@
 	return
 
 /atom/movable/proc/forceMove(atom/destination)
+	if(loc == destination)
+		return 0
+	var/is_origin_turf = isturf(loc)
+	var/is_destination_turf = isturf(destination)
+	// It is a new area if:
+	//  Both the origin and destination are turfs with different areas.
+	//  When either origin or destination is a turf and the other is not.
+	var/is_new_area = (is_origin_turf ^ is_destination_turf) || (is_origin_turf && is_destination_turf && loc.loc != destination.loc)
+
+	var/atom/origin = loc
+	loc = destination
+
+	if(origin)
+		origin.Exited(src, destination)
+		if(is_origin_turf)
+			for(var/atom/movable/AM in origin)
+				AM.Uncrossed(src)
+			if(is_new_area && is_origin_turf)
+				origin.loc.Exited(src, destination)
+
 	if(destination)
-		if(loc)
-			loc.Exited(src)
-		loc = destination
-		loc.Entered(src)
-		return 1
-	return 0
+		destination.Entered(src, origin)
+		if(is_destination_turf) // If we're entering a turf, cross all movable atoms
+			for(var/atom/movable/AM in loc)
+				if(AM != src)
+					AM.Crossed(src)
+			if(is_new_area && is_destination_turf)
+				destination.loc.Entered(src, origin)
+	return 1
 
 //called when src is thrown into hit_atom
 /atom/movable/proc/throw_impact(atom/hit_atom, var/speed)

code/game/objects/structures/crates_lockers/closets.dm

@@ -394,3 +394,6 @@
 	var/shake_dir = pick(-1, 1)
 	animate(src, transform=turn(matrix(), 8*shake_dir), pixel_x=init_px + 2*shake_dir, time=1)
 	animate(transform=null, pixel_x=init_px, time=6, easing=ELASTIC_EASING)
+
+/obj/structure/closet/onDropInto(var/atom/movable/AM)
+	return

code/modules/games/cards.dm

@@ -146,7 +146,7 @@
 		for(var/datum/playingcard/P in cards)
 			H.cards += P
 		H.concealed = src.concealed
-		user.drop_from_inventory(src,user.loc)
+		user.drop_from_inventory(src)
 		qdel(src)
 		H.update_icon()
 		return

code/modules/mob/holder.dm

@@ -50,6 +50,11 @@ var/list/holder_mob_icon_cache = list()
 			continue
 		M.forceMove(get_turf(src))
 
+/obj/item/weapon/holder/onDropInto(var/atom/movable/AM)
+	if(ismob(loc))   // Bypass our holding mob and drop directly to its loc
+		return loc.loc
+	return ..()
+
 /obj/item/weapon/holder/GetID()
 	for(var/mob/M in contents)
 		var/obj/item/I = M.GetIdCard()

code/modules/mob/inventory.dm

@@ -126,16 +126,12 @@ var/list/slot_equipment_priority = list( \
 
 // Removes an item from inventory and places it in the target atom.
 // If canremove or other conditions need to be checked then use unEquip instead.
-/mob/proc/drop_from_inventory(var/obj/item/W, var/atom/Target = null)
 
+/mob/proc/drop_from_inventory(var/obj/item/W, var/atom/target = null)
 	if(W)
-		if(!Target)
-			Target = loc
-
-		remove_from_mob(W)
-		if(!(W && W.loc)) return 1 // self destroying objects (tk, grabs)
-
-		W.forceMove(Target)
+		remove_from_mob(W, target)
+		if(!(W && W.loc))
+			return 1 // self destroying objects (tk, grabs)
 		update_icons()
 		return 1
 	return 0
@@ -194,7 +190,9 @@ var/list/slot_equipment_priority = list( \
 
 
 //Attemps to remove an object on a mob.
-/mob/proc/remove_from_mob(var/obj/O)
+/mob/proc/remove_from_mob(var/obj/O, var/atom/target)
+	if(!O) // Nothing to remove, so we succeed.
+		return 1
 	src.u_equip(O)
 	if (src.client)
 		src.client.screen -= O
@@ -202,7 +200,10 @@ var/list/slot_equipment_priority = list( \
 	O.screen_loc = null
 	if(istype(O, /obj/item))
 		var/obj/item/I = O
-		I.forceMove(src.loc)
+		if(target)
+			I.forceMove(target)
+		else
+			I.dropInto(loc)
 		I.dropped(src)
 	return 1