Adds animation to objects sliding into or out of morgue trays (tgstat…

…ion#83127)

## About The Pull Request


https://github.com/tgstation/tgstation/assets/51863163/b0662ee7-8f67-42d3-95ca-31012556f4ee

This effect is purely visual, objects are still "instantly" put into or
out of the morgue itself. (Meaning you can't grab an object as it is
being shifted in or taken out, nor can you move off the tray while it is
sliding in or out.)

Also applies to crematoriums. 

## Why It's Good For The Game

Adds a tiny bit of visual flair to help "sell" the effect that the tray
belongs to the morgue container, rather than just appearing and
disappearing.

## Changelog

:cl: Melbert
qol: Morgue trays (and the contents inside) are now animated on open and
close
/:cl:

code/game/objects/structures/morgue.dm

@@ -45,6 +45,8 @@ GLOBAL_LIST_EMPTY(bodycontainers) //Let them act as spawnpoints for revenants an
 	var/locked = FALSE
 	///Cooldown between breakout msesages.
 	COOLDOWN_DECLARE(breakout_message_cooldown)
+	/// Cooldown between being able to slide the tray in or out.
+	COOLDOWN_DECLARE(open_close_cd)
 
 /obj/structure/bodycontainer/Initialize(mapload)
 	. = ..()
@@ -131,30 +133,90 @@ GLOBAL_LIST_EMPTY(bodycontainers) //Let them act as spawnpoints for revenants an
 		user.overlay_fullscreen("remote_view", /atom/movable/screen/fullscreen/impaired, 2)
 
 /obj/structure/bodycontainer/proc/open()
-	playsound(loc, 'sound/items/deconstruct.ogg', 50, TRUE)
+	if(!COOLDOWN_FINISHED(src, open_close_cd))
+		return FALSE
+
+	COOLDOWN_START(src, open_close_cd, 0.25 SECONDS)
+	playsound(src, 'sound/items/deconstruct.ogg', 50, TRUE)
 	playsound(src, 'sound/effects/roll.ogg', 5, TRUE)
-	var/turf/T = get_step(src, dir)
-	if (connected)
-		connected.setDir(dir)
-	for(var/atom/movable/AM in src)
-		AM.forceMove(T)
+	var/turf/dump_turf = get_step(src, dir)
+	connected?.setDir(dir)
+	for(var/atom/movable/moving in src)
+		moving.forceMove(dump_turf)
+		animate_slide_out(moving)
 	update_appearance()
+	return TRUE
 
 /obj/structure/bodycontainer/proc/close()
+	if(!COOLDOWN_FINISHED(src, open_close_cd))
+		return FALSE
+
+	COOLDOWN_START(src, open_close_cd, 0.5 SECONDS)
 	playsound(src, 'sound/effects/roll.ogg', 5, TRUE)
 	playsound(src, 'sound/items/deconstruct.ogg', 50, TRUE)
-	for(var/atom/movable/AM in connected.loc)
-		if(!AM.anchored || AM == connected)
-			if(isliving(AM))
-				var/mob/living/living_mob = AM
-				if(living_mob.incorporeal_move)
-					continue
-			else if(istype(AM, /obj/effect/dummy/phased_mob))
+	var/turf/close_loc = connected.loc
+	for(var/atom/movable/entering in close_loc)
+		if(entering.anchored && entering != connected)
+			continue
+		if(isliving(entering))
+			var/mob/living/living_mob = entering
+			if(living_mob.incorporeal_move)
 				continue
-			else if(isdead(AM))
-				continue
-			AM.forceMove(src)
+		else if(istype(entering, /obj/effect/dummy/phased_mob) || isdead(entering))
+			continue
+		animate_slide_in(entering, close_loc)
+		entering.forceMove(src)
 	update_appearance()
+	return TRUE
+
+#define SLIDE_LENGTH (0.3 SECONDS)
+
+/// Slides the passed object out of the morgue tray.
+/obj/structure/bodycontainer/proc/animate_slide_out(atom/movable/animated)
+	var/old_layer = animated.layer
+	animated.layer = layer - (animated == connected ? 0.03 : 0.01)
+	animated.pixel_x = animated.base_pixel_x + (x * 32) - (animated.x * 32)
+	animated.pixel_y = animated.base_pixel_y + (y * 32) - (animated.y * 32)
+	animate(
+		animated,
+		pixel_x = animated.base_pixel_x,
+		pixel_y = animated.base_pixel_y,
+		time = SLIDE_LENGTH,
+		easing = CUBIC_EASING|EASE_OUT,
+		flags = ANIMATION_PARALLEL,
+	)
+	addtimer(VARSET_CALLBACK(animated, layer, old_layer), SLIDE_LENGTH)
+
+/// Slides the passed object into the morgue tray from the passed turf.
+/obj/structure/bodycontainer/proc/animate_slide_in(atom/movable/animated, turf/from_loc)
+	// It's easier to just make a visual for entering than to animate the object itself
+	var/obj/effect/temp_visual/morgue_content/visual = new(from_loc, animated)
+	visual.layer = layer - (animated == connected ? 0.03 : 0.01)
+	animate(
+		visual,
+		pixel_x = visual.base_pixel_x + (x * 32) - (visual.x * 32),
+		pixel_y = visual.base_pixel_y + (y * 32) - (visual.y * 32),
+		time = SLIDE_LENGTH,
+		easing = CUBIC_EASING|EASE_IN,
+		flags = ANIMATION_PARALLEL,
+	)
+
+/// Used to mimic the appearance of an object sliding into a morgue tray.
+/obj/effect/temp_visual/morgue_content
+	duration = SLIDE_LENGTH
+
+/obj/effect/temp_visual/morgue_content/Initialize(mapload, atom/movable/sliding_in)
+	. = ..()
+	if(isnull(sliding_in))
+		return
+
+	appearance = sliding_in.appearance
+	dir = sliding_in.dir
+	alpha = sliding_in.alpha
+	base_pixel_x = sliding_in.base_pixel_x
+	base_pixel_y = sliding_in.base_pixel_y
+
+#undef SLIDE_LENGTH
 
 #define MORGUE_EMPTY 1
 #define MORGUE_NO_MOBS 2
@@ -526,6 +588,7 @@ GLOBAL_LIST_EMPTY(crematoriums)
 	name = "crematorium tray"
 	desc = "Apply body before burning."
 	icon_state = "cremat"
+	layer = /obj/structure/bodycontainer/crematorium::layer - 0.03
 
 /*
  * Morgue tray
@@ -536,6 +599,7 @@ GLOBAL_LIST_EMPTY(crematoriums)
 	icon = 'icons/obj/structures.dmi'
 	icon_state = "morguet"
 	pass_flags_self = PASSTABLE | LETPASSTHROW
+	layer = /obj/structure/bodycontainer/morgue::layer - 0.03
 
 /obj/structure/tray/m_tray/CanAllowThrough(atom/movable/mover, border_dir)
 	. = ..()