Sort some things with the shop but I'm not sure what the error currently means

game/game.gd

@@ -88,9 +88,8 @@ func update_counter_icon():
 	else:
 		store_collector_texturerect.texture = null
 
-func _on_ghost_requested(scene: PackedScene, texture: Texture2D):
-	ghost.scene_to_instantiate = scene
-	ghost.preview_texture = texture
+func _on_ghost_requested(item: PurchasableItem):
+	ghost.COMPAT_set_to_purchasable_item(item)
 	ghost.process_mode = Node.PROCESS_MODE_INHERIT
 	ghost.show()
 

game/shop_item.gd

@@ -14,7 +14,7 @@ class_name ShopItem
 ## The item type to collect to purchase the item.
 ##
 ## If null, counts the items' value.
-@export var cost_tag: StringPath
+@export var cost_tag: StringName
 
 ## The quantity of items to collect to purchase the item.
 ##
@@ -24,8 +24,21 @@ class_name ShopItem
 ## The shape that the ghost should use to determine if the item's placement is valid.
 ##
 ## Concave shapes might have problems interacting with the placeable area.
+##
+## May be null if the purchase does not involve the placement of an item.
 @export var placement_shape: Shape2D
 
+## The texture that should be rendered when the ghost is placing this item.
+##
+## Will be made transparent and modulated to red by the ghost.
+##
+## May be null if the purchase does not involve the placement of an item.
+@export var placement_texture: Texture2D
+
+## The scene to instantiate when the purchase is complete.
+##
+## May be null if the purchase does not involve the placement of an item.
+@export var placement_scene: PackedScene
 
 ## What to do when this item is purchased.
 signal on_purchase

game/shop_item.tscn

@@ -0,0 +1,6 @@
+[gd_scene load_steps=2 format=3 uid="uid://ct4sh7f8qnyob"]
+
+[ext_resource type="Script" path="res://game/shop_item.gd" id="1_8e5vp"]
+
+[node name="ShopItem" type="Node"]
+script = ExtResource("1_8e5vp")

interface/ghost/ghost.gd

@@ -30,34 +30,65 @@ class_name Ghost
 ## The [Sprite2D] node previewing the scene.
 @onready var preview_sprite: Sprite2D = $PlacementShape/PreviewSprite
 
+## The position the ghost should have when a new body starts being placed.
+@onready var starting_position: Vector2 = position
 
-var can_place: bool = false
+## The rotation the ghost should have when a new body starts being placed.
+@onready var starting_rotation_radians: float = rotation
+
+
+## Whether this object can currently be placed.
+var can_place: bool = false:
+	get:
+		return can_place
+	set(value):
+		if value != can_place:
+			can_place_changed.emit(value)
+		can_place = value
+		modulate = valid_color if value else invalid_color
+
+## Emitted when [can_place] changes value.
+signal can_place_changed(to: bool)
 
 
 func _ready():
 	# Initialize the Area's collision mask
-	collision_mask = overlap_checker.collision_mask | placeable_area_checker.collision_mask | overlap_freer.collision_mask
-
+	collision_mask = overlap_checker.overlap_mask | placeable_area_checker.overlap_mask | overlap_freer.overlap_mask
 
 ## Update the value of [can_place].
 func update_state():
 	# DIRTY HACK: Relies on the placeable area being perfectly surrounded by solid bodies.
 	can_place = overlap_checker.is_overlapping_with == null and placeable_area_checker.is_overlapping_with != null
 
+## For retro-compatibility, configure this for the placement of a [PurchasableItem].
+func COMPAT_set_to_purchasable_item(pi: PurchasableItem):
+	instantiator.scene_to_instantiate = pi.item_scene
+	placement_shape.shape = pi.get_node("ConverterPlacementBody").get_node("FullConverterShape").shape
+	placement_shape.scale = pi.item_scene.scale
+	preview_sprite.texture = pi.item_icon
+	position = starting_position
+	rotation = starting_rotation_radians
 
+
+## Configure this for the placement of a [ShopItem].
 func set_to_shop_item(si: ShopItem):
-	pass
+	instantiator.scene_to_instantiate = si.placement_scene
+	placement_shape.shape = si.placement_shape  # TODO: Hmmm. Not the best interface.
+	placement_shape.scale = si.placement_scene.scale
+	preview_sprite.texture = si.placement_texture
+	position = starting_position
+	rotation = starting_rotation_radians
 
+## Emitted when [materialize] is called.
+signal materialized(what: Node)
 
-func materialize():
-	# Compatibility stub for Instantiator
+## Try to materialize the scene, returning it if the instantiation was successful, or null if it wasn't. 
+##
+## Remember to try the placement again if this returns null!
+func materialize() -> Node:
 	if not can_place:
 		return null
-	var overlapping_bodies = get_overlapping_bodies()
-	for body in overlapping_bodies:
-		if body is PhysicsBody2D:
-			if body.collision_layer & collision_mask_delete_placement:
-				body.queue_free()
+	overlap_freer.area_queue_free()
 	var inst = instantiator.instantiate()
-	# TODO: Remove this
+	materialized.emit(inst)
 	return inst

interface/ghost/ghost.tscn

@@ -13,13 +13,9 @@ collision_layer = 0
 collision_mask = 4294967295
 input_pickable = false
 script = ExtResource("1_1bq64")
-valid_color = null
-invalid_color = null
-collision_mask_prevent_placement = 16
-collision_mask_delete_placement = 4
 
 [node name="PlacementShape" parent="." instance=ExtResource("2_bo8dp")]
-scale = Vector2(2.5, 2.5)
+shape = null
 
 [node name="PreviewSprite" type="Sprite2D" parent="PlacementShape"]
 modulate = Color(1, 1, 1, 0.5)

interface/ghost/overlap_freer.gd

@@ -28,10 +28,14 @@ func get_all_overlapping_bodies() -> Array[Node2D]:
 	return bodies
 
 ## Emitted when a body is about to be [queue_free]d.
-signal body_queueing_free(body: Node2D)
+signal queueing_free(body: Node2D)
+
+## Queue free the passed nodes.
+func mass_queue_free(nodes: Array[Node2D]):
+	for node in nodes:
+		queueing_free.emit(node)
+		node.queue_free()
 
 ## Queue free all overlapping bodies.
 func area_queue_free() -> void:
-	for body in get_all_overlapping_bodies():
-		body_queueing_free.emit(body)
-		body.queue_free()
+	mass_queue_free(get_all_overlapping_bodies())

interface/purchasable_item.gd

@@ -90,25 +90,25 @@ var has_bought: bool:
 
 
 ## Emitted when a purchase has started.
-signal purchase_begin
+signal purchase_begin(what: PurchasableItem)
 
 ## Emitted when a purchase is cancelled.
-signal purchase_cancel
+signal purchase_cancel(what: PurchasableItem)
 
 ## Emitted when a purchase is completed.
 ##
 ## Emitted by complete_purchase().
-signal purchase_success
+signal purchase_success(what: PurchasableItem)
 
 
 func _on_buy_button_pressed():
 	if is_buying:
 		is_buying = false
-		purchase_cancel.emit()
+		purchase_cancel.emit(self)
 	else:
 		is_buying = true
-		purchase_begin.emit()
+		purchase_begin.emit(self)
 
 func complete_purchase():
 	is_buying = false
-	purchase_success.emit()
+	purchase_success.emit(self)

interface/shop_ui.gd

@@ -23,14 +23,14 @@ signal purchase_success(what: PurchasableItem)
 ## Array of all PurchasableItems that this ShopUI should control.
 @onready var purchasable_items: Array[Node] = find_children("*", "PurchasableItem")
 
-signal ghost_requested(scene: PackedScene, texture: Texture2D)
+signal ghost_requested(what: PurchasableItem)
 
 
 func _ready():
 	for item in purchasable_items:
-		item.purchase_begin.connect(_on_any_purchase_begin.bind(item))
-		item.purchase_cancel.connect(_on_any_purchase_cancel.bind(item))
-		item.purchase_success.connect(_on_any_purchase_success.bind(item))
+		item.purchase_begin.connect(_on_any_purchase_begin)
+		item.purchase_cancel.connect(_on_any_purchase_cancel)
+		item.purchase_success.connect(_on_any_purchase_success)
 
 func _on_any_purchase_begin(what: Node):
 	if not what is PurchasableItem:
@@ -38,7 +38,7 @@ func _on_any_purchase_begin(what: Node):
 		return
 	delete_button.disabled = true
 	if what.item_scene:
-		ghost_requested.emit(what.item_scene, what.item_icon)
+		ghost_requested.emit(what)
 	purchase_begin.emit(what)
 	set_all_can_buy(false, what)