Add an empty state for BlockCanvas and Picker

https://phabricator.endlessm.com/T35511

Author: dylanmccall

addons/block_code/ui/block_canvas/block_canvas.gd

@@ -6,6 +6,8 @@ const EXTEND_MARGIN: float = 800
 
 @onready var _window: Control = %Window
 @onready var _window_scroll: ScrollContainer = %WindowScroll
+@onready var _choose_block_code_label: Label = %ChooseBlockCodeLabel
+@onready var _create_block_code_label: Label = %CreateBlockCodeLabel
 
 var _block_scenes_by_class = {}
 
@@ -41,10 +43,27 @@ func set_child(n: Node):
 func bsd_selected(bsd: BlockScriptData):
 	clear_canvas()
 
+	_choose_block_code_label.visible = false
+	_create_block_code_label.visible = false
+
+	if not bsd and scene_has_bsd_nodes():
+		_choose_block_code_label.visible = true
+		return
+	elif not bsd and not scene_has_bsd_nodes():
+		_create_block_code_label.visible = true
+		return
+
 	for tree in bsd.block_trees.array:
 		load_tree(_window, tree)
 
 
+func scene_has_bsd_nodes() -> bool:
+	var scene_root = EditorInterface.get_edited_scene_root()
+	if not scene_root:
+		return false
+	return scene_root.find_children("*", "BlockCode").size() > 0
+
+
 func clear_canvas():
 	for child in _window.get_children():
 		child.queue_free()

addons/block_code/ui/block_canvas/block_canvas.tscn

@@ -24,3 +24,17 @@ unique_name_in_owner = true
 layout_mode = 2
 size_flags_horizontal = 3
 mouse_filter = 1
+
+[node name="ChooseBlockCodeLabel" type="Label" parent="."]
+unique_name_in_owner = true
+visible = false
+layout_mode = 2
+text = "Choose a BlockCode node in the inspector."
+horizontal_alignment = 1
+
+[node name="CreateBlockCodeLabel" type="Label" parent="."]
+unique_name_in_owner = true
+visible = false
+layout_mode = 2
+text = "First, add a BlockCode node to the scene."
+horizontal_alignment = 1

addons/block_code/ui/picker/picker.gd

@@ -8,6 +8,10 @@ signal block_picked(block: Block)
 
 
 func bsd_selected(bsd: BlockScriptData):
+	if not bsd:
+		reset_picker()
+		return
+
 	for class_dict in ProjectSettings.get_global_class_list():
 		if class_dict.class == bsd.script_inherits:
 			var script = load(class_dict.path)
@@ -19,10 +23,14 @@ func bsd_selected(bsd: BlockScriptData):
 	init_picker(CategoryFactory.get_inherited_categories(bsd.script_inherits))
 
 
-func init_picker(extra_blocks: Array[BlockCategory] = []):
+func reset_picker():
 	for c in _block_list.get_children():
 		c.queue_free()
 
+
+func init_picker(extra_blocks: Array[BlockCategory] = []):
+	reset_picker()
+
 	var block_categories := CategoryFactory.get_general_categories()
 
 	if extra_blocks.size() > 0: