refactor(card_base)!: 重构 Card Base 代码。

- 删除 card_put 信号。暂不提供替代方案。

- 删除在新逻辑中不使用的函数和变量。

- 将变量 var mouse_on: bool 重命名为 is_mouse_on。

- 重写卡牌回到 Card Base 的逻辑：监听子节点 Cards 的
  child_exiting_tree(node: Node) 信号，当 node 为 Card 时令计数加一。

objects/card_base/card_base.gd

@@ -2,78 +2,64 @@ extends Area2D
 
 class_name CardBase
 
+
+
 const CardScn := preload("res://objects/card/card.tscn")
 const FADE_MOVE_AMOUNT := 70
 
-signal card_put
 
 
-var fade_flag := false
-var mouse_on := false
+var fade_flag := false ## 是否进行淡出处理。
+var is_mouse_on := false ## 鼠标是否在它的上面。
+
 
 enum { DEFAULT, HIGHLIGHT, DISABLED}
-var available_stat := DEFAULT
+var available_stat := DEFAULT ## 当前状态。
+
 
+var card_count = 0 ## 剩余卡牌数量。
 
-var card_count = 0
-var new_card_node: Card
 
+## 更新显示剩余卡牌数量的 Label。
 func update_card_count_label():
-	$Label.text = str(card_count)
+	$Label.text = str(self.card_count)
 
-func _ready():
-	update_card_count_label()
 
+## 设置剩余卡牌数量为 value。
 func set_card_count(value):
-	card_count = value
-	if card_count > 0:
-		if mouse_on:
-			available_stat = HIGHLIGHT
+	assert(value >= 0, "void CardBase::set_card_count(value: int) should only be called with value >= 0.")
+
+	self.card_count = value
+	if self.card_count > 0:
+		if self.is_mouse_on:
+			self.available_stat = HIGHLIGHT
 		else:
-			available_stat = DEFAULT
+			self.available_stat = DEFAULT
 	else:
-		available_stat = DISABLED
+		self.available_stat = DISABLED
 	update_card_count_label()
 
 
+## 生成一张 Card。
+##
+## 当剩余卡牌数量小于等于 0 时不会生成。
 func draw_card():
-	if card_count <= 0:
+	if self.card_count <= 0:
 		return
-	set_card_count(card_count - 1) 
+
+	set_card_count(self.card_count - 1) 
 	$SFXPickUp.play()
-	Input.set_default_cursor_shape(Input.CURSOR_DRAG)
-	new_card_node = CardScn.instantiate()
+
+	var new_card_node: Card = CardScn.instantiate()
 	new_card_node.set_word($Word.get_word())
-	new_card_node.set_position(position)
+	new_card_node.set_position(self.position)
+
 	$Cards.add_child(new_card_node)
-	new_card_node.back_to_origin_global_position.connect(_on_card_back.bind(new_card_node))
-	new_card_node.put.connect(_on_card_put)
 
-	new_card_node._on_mouse_pressed()
-	# prints("new_card_node", new_card_node.name)
+	new_card_node.pick_up()
 
-func _on_card_back(card: Card):
-	set_card_count(card_count + 1)
-	# prints("new_card_node", card.name, "has been removed")
-	$Cards.remove_child(card)
-	card.queue_free()
-	#print("card_count = ", card_count)
-
-func _on_area_entered(area: Card):
-	#prints("Entered", name)
-	if area.get_word() == $Word.get_word():
-		area.on_card_base_entered(position)
-
-func _on_area_exited(area: Card):
-	#prints("Exited", name)
-	if area.get_word() == $Word.get_word():
-		area.on_card_base_exited()
-
-func _input_event(_viewport: Object, event: InputEvent, _shape_idx: int) -> void:
-	if event is InputEventMouseButton:
-		if event.is_pressed() and event.button_index == MOUSE_BUTTON_LEFT:
-			draw_card()
 
+## 设置字符为 e，并更新卡背颜色。
 func set_word(e: String) -> void:
 	$Word.set_word(e)
 
@@ -82,14 +68,15 @@ func set_word(e: String) -> void:
 		ImageLib.update_animation($CardBaseSprite, 1, 1, 1, "res://objects/card_base/card_base%d.png", 
 								  ImageLib.PALETTE["lightblue"], ImageLib.PALETTE[card_type])
 
+
+## 获取字符。
 func get_word() -> String:
 	return $Word.get_word()
 
-func _on_card_put():
-	emit_signal("card_put")
 
+## 进行通关后的处理。
 func set_victory() -> void:
-	# start_fade
+	# 开始淡出
 	fade_flag = true
 	$FadeTimer.start()
 	$CollisionShape2D.set_deferred("disabled", true)
@@ -98,31 +85,46 @@ func set_victory() -> void:
 	for card: Card in $Cards.get_children():
 		card.set_victory(true)
 
-func reset_all_card_position():
-	for card: Card in $Cards.get_children():
-		card.reset_position()
 
+
+func _ready():
+	update_card_count_label()
+
+
 func _process(_delta) -> void:
+	var offset := 0.0
 	if fade_flag:
-		var offset = $FadeTimer.time_left / $FadeTimer.wait_time
-		offset = (1 - pow(offset, 1.5)) * FADE_MOVE_AMOUNT
-		$CardBaseSprite.position.y = offset
-		$HighlightSprite.position.y = offset
-		$DisabledSprite.position.y = offset
-		$Word.position.y = offset
+		var progress: float = $FadeTimer.time_left / $FadeTimer.wait_time
+		offset = (1 - pow(progress, 1.5)) * FADE_MOVE_AMOUNT
+	$CardBaseSprite.position.y = offset
+	$HighlightSprite.position.y = offset
+	$DisabledSprite.position.y = offset
+	$Word.position.y = offset
 
 	$HighlightSprite.visible = (available_stat == HIGHLIGHT)
 	$DisabledSprite.visible = (available_stat == DISABLED)
 
+
+func _input_event(_viewport: Object, event: InputEvent, _shape_idx: int) -> void:
+	if event is InputEventMouseButton:
+		if event.is_pressed() and event.button_index == MOUSE_BUTTON_LEFT:
+			draw_card()
+
+
 
 func _on_mouse_entered():
-	mouse_on = true
+	is_mouse_on = true
 	if available_stat == DEFAULT:
 		available_stat = HIGHLIGHT
 		Input.set_default_cursor_shape(Input.CURSOR_POINTING_HAND)
 
+
 func _on_mouse_exited():
-	mouse_on = false
+	is_mouse_on = false
 	if available_stat == HIGHLIGHT:
 		available_stat = DEFAULT
 		Input.set_default_cursor_shape(Input.CURSOR_ARROW)
+
+
+func _on_cards_child_exiting_tree(node: Node) -> void:
+	set_card_count(self.card_count + 1)

objects/card_base/card_base.tscn

@@ -75,3 +75,4 @@ volume_db = 9.58
 [connection signal="area_exited" from="." to="." method="_on_area_exited"]
 [connection signal="mouse_entered" from="." to="." method="_on_mouse_entered"]
 [connection signal="mouse_exited" from="." to="." method="_on_mouse_exited"]
+[connection signal="child_exiting_tree" from="Cards" to="." method="_on_cards_child_exiting_tree"]