feat(plugin): add terrain3d plugin installation

addons/terrain_3d/src/multi_picker.gd

@@ -0,0 +1,88 @@
+# Copyright © 2023-2026 Cory Petkovsek, Roope Palmroos, and Contributors.
+# Multipicker for Terrain3D
+extends HBoxContainer
+
+
+signal pressed
+signal value_changed
+
+
+const ICON_PICKER_CHECKED: String = "res://addons/terrain_3d/icons/picker_checked.svg"
+const MAX_POINTS: int = 2
+
+
+var icon_picker: Texture2D
+var icon_picker_checked: Texture2D
+var points: PackedVector3Array
+var picking_index: int = -1
+
+
+func _enter_tree() -> void:
+	icon_picker = get_theme_icon("ColorPick", "EditorIcons")
+	icon_picker_checked = load(ICON_PICKER_CHECKED)
+	
+	points.resize(MAX_POINTS)
+	
+	for i in range(MAX_POINTS):
+		var button := Button.new()
+		button.icon = icon_picker
+		button.tooltip_text = "Pick point on the Terrain"
+		button.set_meta(&"point_index", i)
+		button.pressed.connect(_on_button_pressed.bind(i))
+		add_child(button)
+	
+	_update_buttons()
+
+
+func _on_button_pressed(button_index: int) -> void:
+	points[button_index] = Vector3.ZERO
+	picking_index = button_index
+	_update_buttons()
+	pressed.emit()
+
+
+func _update_buttons() -> void:
+	for child in get_children():
+		if child is Button:
+			_update_button(child)
+
+
+func _update_button(button: Button) -> void:
+	var index: int = button.get_meta(&"point_index")
+	
+	if points[index] != Vector3.ZERO:
+		button.icon = icon_picker_checked
+	else:
+		button.icon = icon_picker
+
+
+func clear() -> void:
+	points.fill(Vector3.ZERO)
+	_update_buttons()
+	value_changed.emit()
+
+
+func all_points_selected() -> bool:
+	return points.count(Vector3.ZERO) == 0
+
+
+func add_point(p_value: Vector3) -> void:
+	if points.has(p_value):
+		return
+	
+	# If manually selecting a point individually
+	if picking_index != -1:
+		points[picking_index] = p_value
+		picking_index = -1
+	else:
+		# Else picking a sequence of points (non-drawable)
+		for i in range(MAX_POINTS):
+			if points[i] == Vector3.ZERO:
+				points[i] = p_value
+				break
+	_update_buttons()
+	value_changed.emit()
+
+
+func get_points() -> PackedVector3Array:
+	return points